Biochemistry Flashcards
What is a cell?
Basic structural, functional and biological unit of all living organisms
Smallest unit of life replicate indecently
Require nutrients and produce waste
Describe the cell membrane
Selectively permeable biological membrane separating interior and exterior of cell and protecting from surroundings
Involved in cell adhesion, ion conductivity, cell signalling, attachment surface for cell wall, glycocalyx (glycoprotein-polysaccharide surrounding CM of some bacteria and epithelial) and intracellular cytoskeleton
Describe the phospholipid bilayer
Made of hydrophilic heads and hydrophobic tails
Phospholipids spontaneously form self-sealing bilayers
Due to hydrophobic interior charged ions cannot diffuse
Fluid - components move around easily
Mosaic - variety of lipids and proteins
Describe centrosomes
Associated with nuclear membrane in prophase In mitosis, NM breaks down and centrosome nucleated microtubules (cytoskeleton) interact with chromosomes to build mitotic spindle Mother centrosome (oldest) role in making cilia and flagella
Describe lysosomes
Membrane bound organelle that functions as recycling centre by digesting unwanted material in cytoplasm from extracellular and obsolete intracellular components
Contains hydrolytic enzymes capable of digesting almost all biomolecules: proteins, nucleic acids, carbs, lipids, debris
50+ enzymes all active at about pH 5
Describe the cytosol/ICF
Liquid found inside cells separated into compartments by membranes i.e. mitochondrial matrix separates cells into compartments
Eukaryotes - ICF in CM and part of cytoplasm (mitochondria, plastids, organelles minus internal fluids and nucleus
Describe the vacuole
Membrane bound organelle filled with water containing in/organic molecules (enzymes in solution), sometimes engulfed solids
Formed by fusion of multiple vesicles
Shape and function varies depending on needs and type of cell
Role in autophagy, balance between biogenesis and degradation, lysis and recycling of mis-folded proteins
Describe mitochondria
Membrane bound organelles
Main functions are to produce ATP in TCA (respiration) and regulate metabolism
Role in - signalling through mitochondrial reactive O2 specifies
Regulate - MP, apoptosis, Ca signalling (including Ca-apoptosis), cellular metabolism, heme and steroid synthesis
Have oestrogen receptors (mtERs) thus sensitive to hormones
In liver cells, have enzymes that detoxify ammonia (waste product of protein metabolism)
Describe the smooth ER
Site of lipid, phospholipid and steroid synthesis connected to nuclear envelope
Abundant in cells (ovaries, testes, skin oil glands) that secrete these products
Metabolism of carbs and steroids, drug detoxification, attachments of receptors on CMPs
Muscle cell - regulates Ca ion conc.
Describe the cytoskeleton
Dynamic structure made of microfilaments (actin), microtubules (tubulin) and intermediate filaments (only found in animal cells) forming framework for movement of organelles and cell shape
Describe the Golgi body
Modifies, sorts and packages macromolecules for exocytosis or use with in cell primarily those delivered by RER
Transports lipids and involved in creation of lysosomes
N/O-linked goycosylation
Describe the rough ER
Complex responsible for manufacture of lysosomal enzymes (mannose-6-phosphate marker added in cis-Golgi network)
Manufacture of secreted proteins secreted either constitutively (no tag) or regulatory (clathrin and basic AA in signal peptide)
Initial stage of N-linked glycosylation
Describe a vesicle
Variety of functions
Internal environment different from cytosolic as is separate from cytosol thus used for organising cellular substances
Involved in metabolism, transport, buoyancy control, enzyme storage (ready for immediate release), chemical reaction chambers
Describe ribosomes
Site of gene translation
Attaches to mRNA, reads codon. tRNA with complementary anti-codon recruited bringing specific AA building protein.
Continues until reaches stop codon, if none will remain attached forming complex
Describe the nucleus
Cell control centre: maintains integrity of genes and regulates gene expression
Contains DNA and histone proteins to form chromosomes
Has double membrane enclosing entire organelle isolating from cytoplasm, nuclear envelopes and nucleoskeleton (like cytoskeleton)
Describe nucleolus
Organelle found in nucleus that forms around specific chromosomal a previous in nucleus
Made of proteins and RNA
Transcribe and modify rRNA and integrate ribosomal proteins into immature ribosomes
Stress sensor and able to regulate rRNA synthesis based on cell environment
Describe the differences between prokaryotes and eukaryotes
Lack membrane bound nucleus (have nucleoid) and complex organelles
Ribosomal binding site in mRNA is the Shine Delgarno sequence: 8 bases up from AUG
Have mesosomes - folds inwards in PM that increase SA, can be artefact (damage to PM during chemical fixation)
Have cell wall, capsules and flagella (chemotaxis - movement of organism in response to chemical stimuli
Describe gram +ve bacteria (purple)
Thick cell wall of peptidoglycan which is mesh that gives strength
Cell would be spherical and v sensitive to osmotic changes without
Describe gram -ve bacteria (red)
Complex cell wall external to PM with thin peptidoglycan layer
Have outer membrane with lipopolysaccharides conferring
Structural integrity, resistance to chem. attack, toxicity (septic shock, death)
How do many antibiotics work?
Act by inhibiting cell wall synthesis
B-lactam antibiotics (Penicillins) interfere with peptidoglycan synthesis causing cell lysis
What is pH?
Logarithmic measure of conc. of H+ ions (protons) in solution
pH = -log[H+]
What is the physiological pH of the body and why is this important?
pH 7.4
pH affects solubility of substances and the activity of biological systems thus keeping pH constant is important for body
Blood pH<7.3 acidosis
Blood pH>7.5 alkalosis
Define acid, base, conjugated acid and conjugated base
Acid - proton donator, gains -ve charge
Base - proton acceptor, gains +ve charge
Conjugated acid - species formed from addition of H+
Conjugated base - what is left after acid donates proton
What is the major respiratory acid in the body and how is it formed?
CO2
Dissolved in water forming carbonic acid which dissociates releasing H+
CO2 + H2O H2CO3 H+ + HCO3-
Name some metabolic acids and how they produced
Organic (lactic, uric) and inorganic (sulphuric) produced by metabolism of AAs containing phosphorus and sulphur
Lactic - product of anaerobic glycolysis
Keto acids - ketoacidosis, lack of insulin
Drugs - aspirin
Define buffer
Solution that resists changes in pH when acid/alkali is added to it
Usually a solution of weak acid and its conjugate base
Biological fluids have ENDOGENOUS buffers
How do buffers work?
Weak acid will partially dissociate and salt will fully dissociate allowing H+/OH- ions to be added and equilibrium will shift to replace the lost molecules
As one fully dissociates more ions will be produced and not removed
What are the main buffers in the body and where are they found?
Haemoglobin (HHb) found in red blood cells
Proteins (HProt) in intracellular fluid
Phosphate (H2PO4-) in intracellular fluid
BICARBONATE (CO2->H2CO3) - blood plasma, interstitial fluid
Define buffer capacity
Extent of resistance to pH change i.e. how much acid/base added before pH changes dramatically
What is the dissociation constant?
Kd - Type of equilibrium constant that measures the dissociation of larger compound to split reversible to smaller components
What is pK(a)?
The pH at which 50% of the HA (acid) has ionised
What is the Henderson-Hasselbalch equation?
pH = pK + log[A-]/[HA]
What is the relationship between pH, pKa and ionisation?
If the pKa is higher than pH, acid is less likely to be ionised
What is critical pH?
pH at which tooth becomes unsaturated with respect to Ca and PO43- allowing hydroxyapatite in enamel to dissolve
Region of pH 5.2-5.5
How does saliva protect teeth from decay?
Produces many buffers (principally bicarbonate) which prevent resting pH falling much lower than pH 6.3
What are the main buffers in saliva and how effective are they?
Proteins - not effective as nearly all charged groups from peptide bonds
Phosphate - good but not in high enough conc. to be effective
Bicarbonate - good
What is the role of bicarbonate in plaque?
Acts to neutralise acid rather than buffer acid
Produces H+ pushing reaction to right producing CO2 and H2O - CO2 released as mouth open system
What conc. does carbonic acid stay at in the mouth and what changes?
About 1.3mMol/L
pH and [HCO3-] change, bicarbonate varies with flow rate
What must all AAs have?
Amino (NH2), carboxyl (COOH), H and R group
a-carbon is C atom amino and carboxyl groups are attached
What is the role of side chains?
Are the functional groups
Determine structure, function and charge of AAs
Charged, polar or hydrophilic R groups exposed on surface
Non-polar, hydrophobic R groups buried in interior
What confers an AAs’ optical activity?
An asymmetric C atom - C attached to 4 different groups
All AAs except GLYCINE (R group = H) are asymmetric
What does being asymmetric mean?
Means compound has spatially distinct but chemically identical isomers that are mirror images of each other (enamtiomers)
Both are optically active (rotate plane polarised light) to right (Dextro) or to left (Levo - majority of AAs)
What is a zwitterion?
A molecule that bears groups of opposite polarity
As amino and carboxylic acid groups readily ionise AAs are dipolar/zwitterions
How does the charge of AAs change with increasing pH?
Low pH - amino protonated, carboxyl normal
pH 7 - amino protonated, carboxyl ionised
High pH - amino normal, carboxyl ionised
Define AMPHOTERIC
Molecules that have both acidic and basic groups
AAs are amphoteric
Define anion
A negative ions from gain of e-
Define cations
+ve charged molecule
Name the aliphatic AAs? (Hydrophobic/non-polar)
VIGAL
V - valine I - isoleucine G - glycine A - alanine L - leucine
Name the aromatic AAs
Y+T
Phenylalanine (phenol - aromatic)
Tryptophan (Y + T = aromatic)
Both non-polar
Tyrosine (Y + T)
Name the sulphur containing AAs
MC Sulphur
M - methionine
C - cysteine (can from S-S, stabilise proteins)
MC Sulphure
Name the neutral polar AAs
Hydroxy-Soft Towel
Serine
Threonine
Amide derivates of Acids
Asparagine
Glutamine
What is the ImIno acid?
Proline - causes bends in polypeptides
Name acidic AAs
Aspartic acid
Glutamic acid
COOH R group - ionised at pH 7
Name the basic AAs
Larry is basic
L - lysine
Ar - arginine
His - histidine
LArHis - extra +ve charge
What formula is used to calculate the isoelectric point? How is this calculated for amino acids with 2 carboxyl/amino groups?
pI = (pKa + pKb)/2
a (acidic) = COOH b (basic) = NH2
For 2 carboxyl groups the (pKa1 + pKa2)/2 is used
What is a dalton?
Da is a unit of molecular weight equivalent to 1 H atom
Compares how heavy something is to H
Describe the primary structure of a protein
Unique sequence of AAs held by peptide bonds
Compare structure to find common sequences suggesting members of a multigene family
Describe the secondary structure of proteins
H bonding determines secondary structure either a-helix or B-pleated sheet
Describe boding in and structure of an a-helix
N atom in peptide bond shares H atom with CO group 4 residues upstream
Polypeptide twists around in a spiral, each turn takes 3.6 AAs residues
Describe B-pleated sheets
B strands laterally connected by 2/3 H bonds
Typically 3-10 AAs long
Describe the tertiary structure of AAs
Folding of secondary requiring series of non-covalent interactions
Held by electrostatic, VDWs, disulphide, hydrophobic interactions
What are electrostatic bonds?
Strong interactions between ions/charged groups of opposite charge
In protein called a salt bridge
What are Van der Waals forces?
Weak, close range temporary dipole-dipole interactions
What are disulphide bonds?
Strong covalent S-S bonds between specific cysteine residues
Tend to lock molecule into configuration allowing it to withstand v high temperatures
What are hydrophobic interactions?
Interactions between polar and non-polar molecules causing the spontaneous folding of hydrophobic residues away from water
Describe the quaternary structure of proteins
Association of multiple tertiary polypeptides
Haemoglobin is association of 4 globin groups and 4 heme groups
What is a protein domain?
Part of a polypeptide that can fold independently of polypeptide into compact, stable tertiary structure
Usually identified by presence of prolIne
Can be cut, isolated and studied separately from main chain
What is protein folding?
Process by which higher structures are formed from primary (AA) sequence
What are transitions in shape of tertiary or quaternary structures called?
Conformational changes - proteins may shift between several similar structures in performing their function
(Tertiary and quaternary structures referred to as conformations)
What is the reversible nature of protein folding dependent on?
Primary structure being maintained
What are the three classes of proteins?
Fibrous
Globular
Membrane-associated
Describe globular proteins
Are soluble, nearly all enzymes are globular
Carbonic anhydrase and haemoglobin are examples
Describe carbonic anhydrase
Catalyses interconversion of CO2 + H2O to carbonic acid
Different classes have little sequential or structural similarities but share identical AS thus all perform same function and require a Zn atom
Contains large B sheet in centre
Describe haemoglobin
Assembly of 4 globular protein subunits each composed of protein chain (2 a chains, 2 B chains) tightly associated with prosthetic heme group
What is a prosthetic group?
Non-protein group tightly bound to protein that confers function
Heme has an Fe atom held in heterocyclic ring equally to all 4 N atoms
Fe is site of O2 binding
Describe fibrous proteins
Form rod/wire like shapes, usually structural or storage proteins
AA sequence often lacks repeating units
From unusual 2ndary structures (collagen triple helix) due to cross-links between chains e.g. S-S bonds between keratin
Usually used to construct CT, tendons, bone matrix, muscle fibre
What are keratins and what do they form?
Family of fibrous structural proteins, they are tough and insoluble
Form non-mineralised structures found in reptiles, birds, amphibians, mammals (hair)
Describe the structure of keratin
High proportion of glycine (smallest) and alanine (2nd smallest) AAs
High amounts of cysteine (sulphur containing) required for S-S bridges confer strength, rigidity by permanent, thermally stable cross-links
Describe the structure of keratin monomer and the assembly into intermediate filaments
3 domains: head, rod, tail
Monomers associate to dimers, associate to tetramers, finally to intermediate filaments forming part of cytoskeleton
What is collagen?
Family of fibrous proteins secreted by CTs with triple helix AA structure
28 different types
Unique sequence of glycine-proline/hydroxyproline-alternative AA
What are the 3 type of membrane-associated proteins?
Transmembrane (intrinsic) - cross membrane, usually a-helix Lipid associated (extrinsic) - bound to outer surface Proteins attached to transmembrane protein - increase ionic strength to detach i.e. add NaCl
What are the 2 domains of membrane proteins?
Interdomain - intracellular
Outer domain - extracellular
What are some of the functions of membrane proteins?
Transporters, linkers, receptors, enzymes
Define enzyme
Proteins that catalyse biochemical reactions (biological catalysts)
Define active site
Parts of enzyme that react with substrate (+ cofactors) in reaction
Define co-enzyme
Small, diffusible organic residue that participates in enzyme catalysed reaction, is stable to heat
Define prosthetic group
Coenzyme covalently bound to enzyme so that not removed by dialysis
Define zymogen
Inactive precursor of enzyme
Define holoenzyme
Protein (apoenzyme) with coenzyme/ions required for activity
Define apoenzyme
Protein with coenzyme required for activity, liable to heat
Define substrate
Molecule on which enzyme performs a reaction
What is lysozyme?
An enzyme found in tissue fluids/secretions, tears, saliva, nasal mucus that protects against bacteria by causing cell to lyse and lose cell content
What is peptidoglycan?
Polysaccharide formed from polymerisation of monosaccharides N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
Describe the structure of bacterial cell wall
Made of peptidoglycan - retains high internal osmotic pressure
Layers of repeating peptidoglycan units with peptide chain bound to NAM
Penta-glycine cross-links between last residue of chain and second last of opposite chain - added strength
Describe alpha and beta linkages
Alpha: H atoms of the C atoms in bond in cis formation
Beta: H atoms of C atoms in bond in trans formation
Describe the lysis of the cell wall
Lysozyme hydrolyses B1:4 bond (between C1 and C4) in glycan between NAG and NAM
Occurs rapidly at close to pH 7
What else will lysozyme hydrolyse?
Oligo NAG (min 6 residues) Fit into groove round enzyme that closes on the strand
What are serine proteases?
Enzymes with hyperactive serine residue at active site and appropriately spaced histidine and aspartate resides
Name some serine proteases
Trypsin
Chymotrypsin
Elastase
Thrombin
How do serine proteases work?
Catalyse by breaking peptide bond using charge relay system
Describe the charge relay system
Flow of electrons between 3 AAs making serine hyperactive
AAs are far apart in primary structure but close in 3D structure due to protein folding
Why are proteolytic enzymes secreted as zymogens?
As are hazardous to body so secreted as zymogens that are activated in gut lumen
Give examples of proteolytic enzymes
Pepsinogen
Tryspinogen
Chymotrypsinogen
Describe the activation of pepsinogen
Chief cells in gastric gland produce pepsinogen
Parietal cells produce HCl hydrolyses some peptide bonds to produce pepsin
Left over pepsinogen is hydrolysed again to produce more pepsin
Describe the activation of trypsinogen
Pancreatic duct secretes pancreatic zymogens
Some zymogens converted to trypsinogen which is converted to trypsin by enterokinase (produced by brush border)
Trypsin activates more enzymes such as chymotrypsinogen
Describe the activation of chymotrypsinogen
Inactive state: single polypeptide, 245AAs with 5 SS bridges, three portions of AS caN’T come together
Trypsin cuts bond between Arg15 and next residue - pi-chymotrypsin left
Cut at Leu13 removes dipeptide bond
Cut at Tyr146 and Asn148 removes another - a-chymotrypsin
3 parts held by SS bridges
Active site resides come together
Charge transfer complex with hyperactive serine formed
How is specificity of enzymes dictated?
Pocket close to AS into which an AA side chain may fit thus size and nature of pocket are important
Describe the specificity of trypsin, chymotrypsin and elastase
Trypsin: cuts basic R groups; Asp at bottom of pocket
Chymotrypsin: cuts hydrophobic R; hydrophobic pocket
Elastase: cuts small R; small pocket
Describe the steady state hypothesis
In enzyme catalysed reaction, enzyme and substrate form complex which is a transient state (either breaking down or reversing)
Initially conc. of complex will increase but will become steady as when broken down enzyme will form new complex
What is Vmax?
The velocity a reaction approaches as substrate conc. is increased
What is Michaelis constant (Km)?
Substrate conc. at 1/2Vmax
Dependent on substrate and enzyme
Measures affinity of enzyme for substrate - a high Km confers low affinity
What is the relationship between substrate conc. and velocity?
Michaelis-Menten equation
v = Vmax[S]/(Km+[S])
When [s]=Km v = 1/2Vmax
When [s]»Km v ~ Vmax
What is the importance of Km?
Can use to compare 1 enzyme’s affinity for different substrates or
Multiple enzymes affinities’ for 1 substrate
Describe hexokinase
Phosphorylates glucose
Widespread in tissue
Low Km = high affinity
Always active
Describe glucokinase
Found in liver and pancreas
High Km = low affinity only active at high glucose conc.
At high conc. glucose stored in liver as glycogen, insulin produced by pancreas
Explain the influencing factors of enzymes
Optimum temp. and pH range above optimum will denature and activity will suddenly drop
Increasing temp. increases energy of collisions, internal energy of reactants and number of collisions
What are lipids?
Diverse class of insoluble compounds that don't form polymers Are hydrophobic (mostly hydrocarbons) and soluble in organic solvents (ether, acetone, chloroform)
Give examples of lipids
Fats, oils, fatty acids, triacylglycerols, glycolipids, phospholipids, steroids
What is the main function of fatty acids?
Catabolised generating ATP or used to synthesise triglycerides and phospholipids
Main function of triglycerides?
Energy storage, protection, insulation
Phospholipids main function?
PM
Main function of steroids
Component of many hormones, cholesterol
Describe the structure of fatty acids
Long hydrocarbon chain with terminal carboxylic acid group
Hydrocarbon chain: saturated (no double bonds), monounsaturated (1 C=C), polyunsaturated (2+ C=C)
Unsaturation causes kink in chain
All naturally occurring unsaturated fats are in cis formation whereas trans unsaturated fats found in manufacture of food
Compare saturated and unsaturated fats
Palmitic (C16) is a saturated fat, MP 69.9
Oleic (C18) is monounsaturated, MP 13.4 - C=C makes packing of molecule difficult
Most animal fats are saturated whereas most fish and plant fats are unsaturated
What is glycerol and what is its importance?
Three C substance that forms backbone of fatty acids in fats
Important component of triglycerides and phospholipids
What is triglyceride and describe its structure
Main component of vegetable oil and animal fats formed from the esterification of 3 fatty acids with glycerol
Has chemical structure CH2COOHR-CHCOOHR’-CH2COOHR”; Rs are long alkyl groups
The fatty acids can be all same, different or 2 the same
What is the importance of triglycerides?
Metabolism: contain 2X energy as carbs and proteins
Storage and transport form of fats
High levels linked to atherosclerosis (heart disease, stroke)
What is the role of adipocytes and adipose tissue?
Adipocytes specialised for synthesis and storage of triglycerides
Found in subcutaneous layer and in abdominal layer
Subcutaneous fat provides insulation
What is lipolysis?
Breakdown of triglycerides into glycerol and fatty acids with release of energy
Fatty acids released into blood, circulate body
Describe the catabolism of glycerol
Converted to glyceraldehyde 3-P and then glucose OR enter TCA depending on ATP supply
Describe the catabolism of fatty acids
Enzymes remove 2C atoms at a time to acetyl CoA to enter TCA
Describe the process of FA activation
Acetyl-CoA synthases esterify long chain FAs to acyl-CoA
Is ATP dependant
Describe the process of FA oxidation
Acyl-CoA dehydrogenase removes H2 from acyl-CoA, NAD is reduced to NADH2, acetyl-CoA oxidised to trans-enoyl-CoA
enoyl-CoA hydratase, hydrates trans-enoyl-CoA to B-hydroxyacyl-CoA
B-hydroxyacyl-CoA dehydrogenase oxides B-..-CoA to B-ketoacyl-CoA
Acyl-CoAacetyl-transferase moves acetyl forming acyl-CoA (2Cs shorter) + acetyl-CoA
What is lipogenesis?
Synthesis of lipids (anabolism) from smaller units
Mainly occurs in liver and adipose tissue in conditions of excess sugar as glucose converted to glycogen
It doesn’t appear to be essential
Compare glucose and fructose
Glucose used in cells throughout body, fructose only in liver
Glucose converted to glycogen, some to FAs and triglycerides
Fructose converted to acetyl them FAs and triglycerides
What are essential fatty acids?
FAs that are required in human diet as humans lack specific enzyme so cannot be synthesised by the body
What can a deficiency of a-linoleic acid and linoleic acid lead to?
Dry scaly rash, decreased growth (children/infants), susceptibility to infection, poor wound healing
Present in variety of foods, represent omega 3 and 6 category of lipid structure
Describe the structure of phospholipids
2 FAs and P group attached to glycerol
FAs from hydrophobic tail, P and its attachment form hydrophilic head
What is meant by amphipathic?
Molecule with both hydrophobic and hydrophilic groups
Describe saturation in phospholipids
1 chain saturated, other not
Degree of saturation alters ability of molecules to pack, affects fluidity
What is the function of cholesterol?
Controls permeability of membrane
Makes membrane less flexible due to rigid steroid ring
Describe glycolipid structure
2 hydrophobic tails, hydrophilic region with 2+ sugar residues i.e. phospholipids without P
What is the function of glycolipids?
Make up 5% of outer monolayer
Sugar groups exposed on cell surface protect and modulate membrane function
Insulating agents in nerve cells (gangliosides)
Describe the structure of steroids
Lipids characterised by C skeleton of 4 fused rings
What is the role of steroids?
Cholesterol: high levels cause atherosclerosis
Hormones: testosterone, oestrogen, cortisol (synthesised from cholesterol) control metabolism, development of sexual characteristics, immune functions
What is a lipoprotein?
Biochemical assembly that contains both proteins and lipids
What is the function of lipoproteins?
Transport insoluble lipids in plasma
Non-polar lipids (triglycerides) contained in hydrophobic centre, polar lipids (phospholipids) form coat
What are apoproteins?
Protein components of lipoproteins
Interact with cellular receptors and determine the metabolic fate of lipoproteins
Explain LDL and HDL
LDLs carry FAs in blood for use by cells but also deposit on artery walls (bad)
HDLs carry LDLs away from artery walls (good)
What are some of the ways to treat hypercholesrerolemia?
Reduce intake (egg yolk, liver, oily fish)
Reduce absorption uptake - zetia, ezetro, niacin
Statins - block enzyme in synthesis of cholesterol
What are the 2 classifications of carbs?
Simple - monosaccharides
Complex - disaccharide, oligosaccharide(2+), polysaccharide (many)
Describe monosaccharides
Simple sugars: can’t be converted into smaller molecules by acid hydrolysis
1 sugar, usually colourless, water-soluble, crystalline solids
Building blocks of di and polysaccharides
Describe the structure of monosaccharides
Generally have formula (CH2)n - deoxyribose is an exception
Simple monosaccharides C4-7 called tetroses, pentoses, hexoses, heptoses
Exceptions in animals N-acetyl sugars (8C), sialic acid (9,10,11C)
What are 2 classifications of monosaccharides?
Aldose and ketose
Aldose - -CHO (aldehyde group)
Ketose - C=O (ketone group)
e.g. aldopentose or ketopentose
Describe the structure of glucose in both straight chain and ring
C6H12O6 Is an aldose sugar i.e. has -CHO Ring: C1 binds to C5 - C1-O-C5 O enables C atoms to bind to from ring H from C5 OH binds to O on C1, C1 binds to O
Describe the structure of fructose
C6H12O6
Is a ketose i.e. has C=O on C2
Ring: C2 bonds to C5
H of C5 OH binds to O of C2, C2 binds to O on C5
What is stereochemistry?
Study of spatial 3D relations of atoms in molecules
What are Fischer projections?
Basic 2D drawing of 3D molecule
C1 is always at top
Projections drawn to left are ABOVE the ring
Projections to right are BELOW the ring
Explain D and L sugars
D and L sugars are optical isomers (mirror images of each other)
D and L refer to the absolute configuration of asymmetric C furthers away from aldehyde/ketone group OR if OH falls on either LHS/RHS
D-glucose is biologically active, OH of C5 falls on RHS
What is the structure of D-glucose?
OH of C2,4,5 to right
OH of C3 to left
L-glucose is opposite
What happens in solution of glucose in terms of structure?
Equilibrium favouring ring form established
Ring formation creates new chiral centres - C1 in aldoses, C2 in ketoses
This increases the number of possible isomeric forms
What are isomers of D-glucose called?
Anomers
Describe the 2 anomers of D-glucose
Alpha - (new) OH of C1 is TRANS to CH2OH on C5
Beta - OH of C2 is CIS to CH2OH on C5
What is mutarotation?
Interconversion between anomer stereoisomers
Different anomers have different optical rotations
What are monosaccharide derivatives?
Simple sugar molecules which contain functional groups as well as OH, either CHO/CO, vary from empirical formula
Describe deoxy derivatives
OH replaced by H
e.g. deoxyribose sugar - ribose with OH on C2 replaced by H
Describe sugar acid derivatives
OH group oxidised to COOH
Describe sugar alcohol derivatives
CO (aldehyde or ketone) reduced to primary/secondary OH
Describe phosphorylated sugars
P group attached
Alcoholic group esterified with phosphoric acid
What are amino sugars?
Sugar with primary amine group replacing OH
e.g. glucosamine precursor for GAGs (major component of joint cartilage) thus used to treat osteoarthritis
Explain the formation of disaccharides
Aldehyde/ketone group reacts with molecules own OH to form ring, then link to C bearing OH on another sugar molecule creating a disaccharide
How are monomers linked?
Glycosidic bonds formed when anomeric OH group condenses with alcohol of second monosaccharide
Catalysed by hydrolyse (dehydration) to form R-O-R link
Describe the structure of sucrose
Glucose and fructose monomers linked by alpha 1,2 linkage
What is glycogen?
Polysaccharide that is the principal storage form of glucose found as granules in cytosol
Liver cells have highest conc. but muscles have greater total amount
Describe the structure of glycogen
Highly branched (increases packing) Linear chains of glucose connected by a-1,4 glycosidic linkages with branches attached through a-1,6 links every 10 residues
What 2 enzymes are required for glycogen degradation and why?
Glycogen phosphorylase to hydrolyse a-1,4 linkages but can only work on linear chains OR a-amylase (digestive)
Debranching enzyme to hydrolyse a-1,6 links to straighten out chain
Describe the degradation of glycogen
Glycogen phosphorylase breaks glycogen into glucose-1-P but is halted 4 residues from branching point
Glycogen debranching enzyme transfers trisaccharide to a-1,4 adjacent a-1,4 link leaving single glucose molecule at a-1,6
GDE hydrolyses remaining glucose molecule so glycogen phosphorylase can continue
Describe the structure of starch
(C6H10O5)n
2 polysaccharides monomers: amylose, amylopectin
Amylose: glucose monomers linked by a-1,4 links
Amylopectin: coiled structure, like glycogen but a-1,6 branch every 24-30 residues
What is the function of starch?
Digested by hydrolysis, catalysed by amylases, back to sugar monomers which can be broken down to glucose for energy
What is cellulose?
Polymeric polysaccharide of B-glucose monomers
What is the function of cellulose?
Primary structural component of cell wall of green plants
Lignin and cellulose (lignocellulose) most common biopolymer on earth
Only tunicates evolved the ability to create and use cellulose
Indigestible by humans so acts as hydrophilic bulking agent for faeces
Describe the structure of cellulose
Layered linear chains of B-1,4 linked D-glucose units packed into crystals (myofibrils)
Layers linked by H bonds
What is lactose?
Disaccharide of B-D-galactose and B-D-glucose linked through B-1,4
What are glycosaminoglycans? (GAGs)
Large, pure carbohydrates that are -ve charged, hydrophilic
Polysaccharides present on animal cell surface and in ECM
Describe the structure of GAGs
Disaccharide repeating unit containing glucosamine or galactosamine and uronic acid
At least one of the sugars has a -ve charged carboxylate or sulphate group - with exception of hyaluronic acid (no sulphate group)
What is a glycoprotein?
Macromolecule composed of protein and a carbohydrate which is added in posttranslational modification either at asparagine (N-glycosylation) or hydroxylysine/hydroxyproline/serine/threonine (O-glycosylation)
What is the function of glycoproteins?
Assist protein folding or improve stability
Immune cell recognition: antibodies (immunoglobulins) interact directly with antigens, moles of major histocompatibility complex (MHC) surface of cells interact with T-cells (adaptive immune response)
Explain N and O glycosylation
Glycosylation is the attachment of carbohydrate to AA side chain
N: attach to N of amide side chain (asparagine)
O: attach to O of OH side chain (hydroxylysine/hydroxyproline/serine/threonine)
What are proteoglycans?
Heavily glycosylated glycoproteins - core protein with several GAG chains
What are the functions of GAGs?
Structural: ECM and BM
Space-filling in cartilage
Modifiers/activators of effector proteins (growth factors, proteases)
What are the functions of proteoglycans?
Form large complexes in ECM with proteoglycans and fibrous matrix proteins (collagen)
Binding of cations and water
Regulation of movement of molecules through matrix
What is chondroitin sulphate?
Sulphate GAG composed of N-acetyl-galactosamine and glucuronic acid
Usually forms part of a proteoglycan
What is the function of chondroitin sulphate?
Major structural component in cartilage conferring resistance to compression
Dietary supplement for treatment of osteoarthritis
What is heparin?
Highly sulphated GAG used as injectable anticoagulant and used for inside of test tubes, renal dialysis machines
Describe the structure of peptidoglycan
Crystal lattice of linear chains of NAG and NAM
Each NAM has peptide chain usually containing AAs that do not occur in humans thought to protect against attacks by most peptidases
Describe the energy balance in humans
Balance between energy intake and energy expenditure
Describe the anabolism of glucose
Glucose enters cell, undergoes glycogenesis forming glycogen in liver and muscle cells
OR undergo lipogenesis and join FA chain
Describe the anabolism of FAs
FAs esterified to triglycerides in adipose tissue
Describe the anabolism of AAs
AAs undergo protein synthesis to form proteins in muscle
Describe the metabolism of glycogen
Glycogen undergoes glycogenesis forming glucose, undergoes glycolysis to pyruvate converted to acetyl-CoA enters TCA
Describe metabolism of triglycerides
Undergo lipolysis forming FAs, undergo B-oxidation to form acetyl-CoA enter TCA
Describe protein metabolism
Proteolysis converts to AAs either directly enter TCA or converted to acetyl-CoA
Describe glycogen stores and their mobilisation
In liver glycogen converted to glucose-6-P which is converted to glucose which can enter brain or back to glucose-6-P and used by muscles to produce lactate
Muscle cells produce glucose 6P then lactate
Describe the cori cycle
Lactate produced in muscle cell converted to pyruvate which can enter gluconeogensis to re-form glucose which can be recycled
Describe lipid stores and mobilisation
Triglyceride stored in adipose broken down to glycerol and FAs
Glycerol undergoes gluconeogenesis forming glucose, enters brain
FAs enter muscle or undergo ketogenesis forming ketone bodies utilised by brain or enter muscle
Describe protein utilisation
Undergo proteolysis produce AAs which can enter TCA, converted to Acetyl-CoA or undergo transamination (amino group moved)
Acetyl-CoA enter TCA or converted to ketone bodies
After transamination form pyruvate either enter TCA or gluconeogenesis
Describe glucose transport
Enters cells via facilitated diffusion by GLUTs
Uptake increased by increasing GLUTs in PM - insulin or exercise
Describe FA transport
Thought to diffuse across PM or may involve FA transporter proteins
How is energy stored in cells?
In chemical bonds
When cell has enough energy available it stores it by adding Pi group to ADP forming ATP
What are the stages of ATP production?
Digestion
Glycolysis
TCA
Describe digestion
Food stuff digested
HCl in stomach
Enzymes - mouth, stomach, small intestine
Enzymes in lysosomes for internal cell digestion
Absorption through cells in SI, enter bloodstream then cells
Describe glycolysis
Starts in cytoplasm
Glucose broken down to 2 pyruvate molecules
2ATP and NADH produced per pyruvate
Pyruvate molecules move to mitochondria where converted to CO2 and 2C acetyl group which attaches to CoA
Describe the structure of CoA
8 trimers of lipoamide reductase-transacetylase
6 dimers of dihydrolipoyl dehydrogenase
12 dimers pyruvate decarboxylase
What are the functions of the three enzymes in CoA?
Pyruvate decarboxylase - removes CO2
Lipoamide reductase transacetylase - transfer acetyl group
Dihydrolipoyl dehydrogenase - reduces NAD
What happens in glycolysis in anaerobic conditions?
Fermentation
Muscle: pyruvate reduced to lactate reforming NAD+
Yeast: pyruvate reduced forming CO2 and acetaldehyde which is reduced to ethanol reforming NAD+
Describe stage 3 of ATP production
Acetyl group enters TCA where it is oxidised to CO2 and large amounts of NADH generated
NADH passed along electron transport chain where energy released produces ATP and consumes O2
What is oxidative phosphorylation?
ATP formation driven by transfer of electrons from food molecules to molecular O2
Electron ends up on O2, with H+ H2O formed
Name the 4 complexes of the electron transport chain
- NADH dehydrogenase
- Succinate dehydrogenase
- Coenzyme Q reductase
- Cytochrome c reductase
What are the roles of the complexes in electron transport chain?
NADH dehydrogenase, succinate dehydrogenase, coenzyme Q reductase pump protons across membrane into intermebrane space making intermembrane increasing acidic
Cytochrome c reductase give electron to O2 producing H2O
How does the electron transport chain produce ATP?
Due to the high H+ conc. in intermembrane space, protons diffuse down conc. gradient through ATP synthase producing lots of ATP
Name and describe the inhibitors of electron transport chain
Rotenone: blocks NADH from being oxidised by NADH dehydrogenase
Antimycin A: blocks complex 2
CN or CO: prevent O2 being reduced by cytochrome c reductase
What is the role of reactions?
Create order within cells: smaller molecules used to make macromolecules
Define catabolism and anabolism
Catabolism: break down of molecules releasing energy
Anabolism: construction of complex molecules from simple ones, storage of energy
Define free energy
Gibbs free energy (G): measure of energy contained in a molecule due to vibration, rotation, bonds
What is delta G?
Changes/difference in free energy
DG = G(products p) - G(reactants)
Define exergonic and endergonic
Exergonic: releases energy to surroundings -DG
Endergonic: absorbs free energy +DG
Define activation energy
Energy difference between reagents and transition state i.e. energy required for reaction to progress
How do enzymes work in terms of EA?
Lower the EA allowing larger proportion of random collisions with surrounding molecules to push substrate over EA
How do enzymes work?
Bind substrate tightly holding it in a way that facilitates conversion to product
Explain coupled reactions
Favourable (oxidisation of glucose) reactions release energy which is captured in chemical form and used to power unfavourable reactions (forming peptide bond)
Favourable reactions take place spontaneously whereas unfavourable only occur if coupled
What are carrier molecules?
Small proteins that contain 1+ energy-rich covalent bond and diffuse rapidly throughout cell thus carry bind energy from generation to utilisation
How do carrier molecules (coenzymes) store their energy?
In easily transferable groups/high-energy electron (easily oxidised/reduced) - ATP, NADH, NADPH
Describe the synthesis of a polynucleotide
Nucleoside monophosphate activated by sequential transfer of terminal P from 2 ATP
High energy intermediate (nucleoside triphosphate) exists freely until reacts with growing end of R/DNA releasing pyrophosphate
Hydrolysis of pyrophosphate to Pi highly favourable, drives overall reaction
Explain the limits of ATP
DG of ATP is -7.3kcal/M only drive reaction up to that amount
If reaction requires more ATP hydrolysis altered to produce AMP and PPi (pyro) which is hydrolysed producing large amounts of free energy
What is the importance of enzyme inhibitors?
Info about shape of AS and AA residues at AS
Info about chemical mechanism
Info about regulation/control of metabolic pathway
Aide drug design
What are the 2 broad classifications of inhibitors?
Reversible
Irreversible: usually involves formation or breaking of covalent bonds - enzyme forms covalent bond with AS so cannot be removed
What are the 3 types of reversible inhibitors?
Competitive
Non-competitive
Uncompetitive
Explain irreversible inhibition
Inhibitor forms covalent bond with AS of enzyme so is permanently attached thus permanently inactivates enzyme
e.g. diisopropylphosphofluoridate prototype for nerve gas sarin, permanently inactivates serine proteases
Explain competitive inhibition
Inhibitor competes with substrate to bind on AS
Inhibitor and substrate have similar structures
ONLY binds to enzyme NOT ES complex
Explain the effect of competitive inhibitors on Vmax and Km
Reduces amount of free enzyme available for substrate binding (forms EI complex) thus Km increased, Vmax unchanged but requires more substrate to reach
Give an example of competitive inhibition
Succinate is converted to fumarate by succinate dehydrogenase
Malonate is a competitive inhibitor for this reaction
How is competitive inhibition reversed?
Increase conc. of substrate to overcome reduced affinity
Explain non-competitive inhibition
Inhibitor binds to separate, distinct binding site causing SLIGHT conformation change
Can bind to E or ES and from ESI complex which is inactive
Explain the effect on Vmax and Km of non-competitive inhibition
As substrate can still bind Km remains constant
As ESI inactive Vmax reduced
Give an example of non-competitive inhibition
Fructose-1,6-diphosphate converted to fructose-6-phosphate by fructose-1,6-bisphosphatase which is inhibited by AMP (binds to separate site) and no fructose-6P produced
Explain uncompetitive inhibition
Binding of substrate allows inhibitor to bind forming inactive ESI complex
Inhibitor ONLY binds to ES
Explain the effect of uncompetitive inhibition on Vmax and Km
Vmax decreased as enzyme inhibited
Km also reduced as creates better ES binding as only binds to ES (due to equilibrium and Le Chatelier’s Principle)
What are allosteric modulators?
Substances which can regulate enzyme activity
Explain the 2 types of allosteric modulators
Positive: increase enzyme activity, binds to allosteric site causing conformational change to enhance substrate binding
Negative: decrease activity, binds to site causing conformational change to decrease substrate binding
What 2 hormones are responsible for regulation of glucose levels?
Insulin: promotes uptake and conversion to glycogen
Glucagon: promotes breakdown of stored glycogen to glucose
Name the 2 conditions caused by excess and lack of glucose
Hyperglycaemia: excess glucose, hallmark of diabetes, glucosuria (glucose toxicity)
Hypoglycaemia: lack of glucose, loss of cognitive function, coma, permanent brain damage
How is glucose transported into cells in the body?
Intestine: uptake from lumen to epithelial requires active transport
Body: blood to cells (muscle, liver, adipose) passive or facilitated diffusion
How is glucose uptake mediated?
GLUT transporters mediate glucose transport into liver, adipose, muscle tissues
Describe GLUTS 1-4
GLUT1+3: PM throughout body, low Km 1mM (high affinity), maintain basal blood glucose 3-6mM
GLUT2: liver, pancreatic cells, high Km 15-20mM, (low affinity as liver stores, pancreas produces insulin in high conc)
GLUT4: muscle, adipose, low Km, insulin sensitive (phosphorylated by Metformin (anti-diabetic) increasing insulin sensitivity)
How is glucose uptake regulate by insulin and exercise?
Uptake into muscle and adipose increased by insulin which increases no. of GLUT4 transporters in PM (GLUT4 containing vesicles fuse with PM)
Insulin resistance associated with fewer GLUT4 transporters
Exercise recruits GLUT4 transporters to PM in muscle
Describe the alternative fates of glucose
Converted to glucose-6P either enter pentose phosphate pathway produce 5C sugar OR glycolysised to pyruvate (gluconeogenesis reproduce glucose-6P)
Explain the role of hexokinase in glycolysis
Found in most cells throughout body, phosphorylates glucose to glucose-6P (1st step of glycolysis)
Low Km
Allosteric inhibition by own product (glucose-6P)
Inhibition of HK causes increase in intracellular glucose inhibiting GLUT transporter
Explain the role of glucokinase in glycolysis
Phosphorylates glucose in liver and pancreatic B cells
Higher Km - only active when glucose levels are high
In B cells acts as glucose sensors for insulin secretion
Not inhibited by glucose-6P
Outline the 10 steps of glycolysis
G-glucose G-glucose-6P F-fructose-6P F-fructose-1,6-bisphosphate G-glyceraldehyde-3P (+ dihydroxyacetone-P) G-glyceraldehyde-3P B-1,3-bisphosphoglycerate P-3-phosphoglycerate P-2-phosphoglycerate P-phosphoenolpyruvate P-pyruvate
H-hexokinase P-phosphoglucose isomerase P-phosphofructokinase A-aldolase T-triosephosphate isomerase G-glyceraldehyde-3P dehydrogenase P-phosphoglycerate kinase P-phosphoglycerate mutase E-enolase P-pyruvate kinase
Explain how phosphofructokinase 1 regulates glycolysis
High ATP conc. allosterically inhibits PFK1 by binding, promotes tense conformation with low affinity for fructose-6P
PFK2 convert fructose-6P to fructose-2,6-bisP (+ ADP) high levels of fructose-2,6-bisP relieves inhibition
High levels of citrate (1st intermediate TCA) inhibits as confers ATP already present
ADP, AMP(extensive ATP hydrolysis) relieve inhibition
Define kinases and mutases
Kinase: phosphorylates i.e. transfers PO4 from ATP to substrate
Mutase: transfer PO4 from 1C to another within molecule
Describe fermentation
Anaerobic organisms lack respiratory chain, NADH reoxidised as pyruvate converted to more reduced compound
Some organisms convert pyruvate to ethanol oxidising NADH in reaction catalysed by alcohol dehydrogenase
Explain how NADH enters the matrix of mitochondria
Oxaloacetate reduced to malate oxidising NADH
Malate enters matrix is oxidised to oxaloacetate reducing NAD+
Oxaloacetate converted to aspartate by glutamate forming a-ketoglutarate
Aspartate leaves matrix, reacts with a-ketoglutarate reforming oxaloacetate and glutamate
Describe galactose metabolism
Gladstone phosphorylated to galactose-1P by galactokinase
UDP-glucose reacts with galactose-1P converting to glucose-1P and forming UDP-galactose
Glucose-1P P group moved by phosphoglucomutase to glucose-6P
What is the importance of Ca?
Bone: provide structural integrity of skeleton
Biochemical processes: neuromuscular excitability, blood coagulation, hormonal secretion, enzymatic regulation
Why must Ca conc. be maintained?
As has role in so many processes extra and intracellular conc. must be maintained
Describe the regulation of intracellular [Ca]
Stored in mitochondria and ER
‘Pump-leak’ transport system: Ca leaks into cytoplasmic compartment, actively pumped into storage sites in organelles to shift away from cytosolic pools
What are the 3 fractions of Ca in serum?
Ionised - 50%
Protein-bound - 40%
Complexed to serum constituents - 10%
What protein is the majority of protein-bound Ca bound to?
Albumin -90%, binding is pH dependent
Rest is bound to globulins
What 2 molecules is Ca complexed to?
Citrate
Phosphate
Describe the effect of acute alkalosis on Ca binding
Inc. Ca binding, dec. ionised Ca
Causes inc. neural excitability and prone to seizures due to low ionised Ca in ECF causing inc. permeability to Na+
Describe Ca turnover
1000mg intake
350mg absorption to ECF (1000mg) and exchangeable pool (4000mg)
500mg used and retrieved in bone remodelling
1000000mg stored in skeleton
200mg excreted in urine
150mg secreted into gut
800mg excreted in faeces
What factors determine the conc. of serum Ca?
Intestinal absorption, renal excretion, bone remodelling
Explain +ve and -be Ca balances
+: intestinal Ca absorption exceeds urinary excretion, difference deposited in growing bones
-: intestinal absorption less than urinary excretion
What are the 3 hormones involved in regulating Ca homeostasis?
Calcitonin
Parathyroid hormone
Calcitriol
How does calcitonin work and what is its effect?
Gs-couple: inc. cAMP, inhibit osteoclast, less Ca resorption, more Ca incorporated into bone tissue
Dec. Ca2+
Stimulated by inc. Ca2+ in plasma
What is the function of PTH and what are its actions?
Inc. Ca
Inc. bone resorption
Inhib. renal P reabsorption in proximal tubule - excreted in urine
Inc. renal Ca reabsorption in distal tubule
Inc. intestinal Ca absorption indirectly by stimulating production of 1,25-dihydroxycholecalciferol
What is the function of calcitriol?
PTH-like effect in bone
Mediated effects of PTH absorption of Ca and P by gut
Where is calcitonin formed and secreted?
Parafollicular cells of thyroid
Where is PTH formed and secreted?
Parathyroid gland
How is the secretion of PTH regulated?
Negative feedback: secreted as serum Ca2+ falls
How is VitD synthesised?
- Skin cells convert 7-dehydrocholesterol to pro hormone cholecalciferol (B3) using sunlight
- Liver then kidney convert pro hormone to active VitD3 (1,25-dihydroxycholecalciferol/dihydroxy-D3)
What are the actions of VitD3?
- Inc. intestinal Ca absorption
- Inc. intestinal P absorption
- Inc. renal reabsorption of Ca and P
- Inc. resorption of bone
What are osteomalacia/rickets?
Conditions caused by VitD deficiency leasing to poor bone mineralisation reducing bone mass thus making bones weak
What are the 2 types of osteomalacia?
VitD-responsive
VitD-resistant
Describe VitD responsive osteomalacia
Caused by deficiency in dietary intake of VitD precursors, inadequate sunlight exposure, malabsorption of Ca
Describe the 2 forms of VitD-resistant osteomalacia
Pseudo-VitD: end-organ hyposensitivity
Hereditary VitD-resistant rickets: VitD receptor has poor affinity for its DNA due to mutation in the DNA binding domain
What is osteoporosis and what are the 2 types?
Dec. in bone strength
Primary: post menopause lose bone rapidly; calcitonin treatment as slows bone resorption
Secondary: caused by corticosteroids, Cushing’s syndrome, immobilisation, GI disease, alcohol, age
senile due to dec. 1,25-dihydroxy-D3 secretion, dec. PTH levels
Explain the evidence showing DNA is heredity genetic material
Virulent lysates contain inheritance materials that transformed harmless bacteria to virulent bacteria killing mouse
Protein/RNA digestion (protease, ribonuclease) didn’t destroy inheritance material - mouse died
DNA digestion destroyed inheritance material preventing bacterial transformation thus mouse lived
Describe the structure of DNA
Linear polymer of 4 nucleotides - adenine, thymine, guanine, cytosine - each made of base, phosphate group and deoxyribose sugar
Nucleotides are linked by phosphodiester bonds and antiparallel strands held in double helix by H bonds between complementary base (AT, GC)
What are the 3 DNA conformation?
B A Z
B most prominent but flexible nature of helix allows A Z conformations
What is the Central Dogma Theory?
Specific DNA gene sequence gets transcribed into RNA, then translated into unique proteins
Describe the process of DNA replication
- Helicase unwinds double helix forming replication fork
- Single-stranded DNA binding proteins stabilise SSDNA to prevent rebinding to double helix
- RNA primase synthesises short fragments of RNA primer required for initiation of DNA synthesis by DNA polymerase 3
- DNA polymerase 1, DNAse H replace RNA primers with DNA
- DNA ligase joins Okazaki fragments (lagging strand) to create continuous newly synthesised DNA
What are genes?
Basic unit of heredity in all living organisms
What is the function of genes?
Encode for proteins essential for biological functions and structures
Some produce non-coding RNA molecules that play role in protein biosynthesis and gene regulation
What are the molecules that result from gene expression called?
Gene products
How do cells read the genome?
DNA doesn’t direct protein synthesis directly, use RNA intermediate used as template for protein synthesis
Central Dogma of molecular biology
Compare DNA and RNA
Sugar: DNA - deoxyribose; RNA - ribose
Bases: ATGC; AUGC
Structure: double stranded helix; single strand (siRNA is double)
Describe the process of transcription
- Small portion of DNA unwound
- Only 1 of DNA strands acts as RNA template
- RNA chain produced called transcript
- RNA polymerase catalyses formation of phosphodiester bonds, moves stepwise along DNA, unwinding DNA helix to expose new region
- Extended 1 nucleotide at a time in 5’-3’ direction
What is the significance of the direction of RNA polymerase?
Determines which DNA strand will be used as template as only work in 5’-3’ direction
Name and describe the role of the main transcription factors (TF)
TFIID + TBP: binds TATA-box in promoter region near imitation site
TFIIA/B: binds TFIID/TBP forming complex for RNA polymerase to bind
RNA polymerase: initiates transcription of RNA from DNA, requires ATP
What are the 2 types of RNA?
Coding - 4% (mRNA)
Functional - 96%
What are the 6 types of functional RNA?
rRNA: component of ribosomes where protein synthesis occurs
tRNA: carry AAs to ribosomes
Small nuclear: splice hnRNA to mRNA
Small nucleolar: chemical modification of rRNA
Micro + short interfering: regulate gene expression in eukaryotic cells
What are the types of post-transcriptional RNA processing?
End-modification
Splicing
Cutting
Chemical modification
How is pre-mRNA converted to mRNA?
snRNPs bind to intron forming loop that pulls exons together
Intron loop is excised and exons spilled together forming mature mRNA
What is mRNA translation?
Conversion of info. in mRNA into protein
What are the rules of the genetic code?
Sequences of nucleotides in mRNA read in codons (groups of 3) each specifying an AA or stop signal
Define what is meant by degenerate
Many codons are redundant as encode the same AA
What is the binding of AAs dependent on?
tRNAs that recognise and bind both to codon (via complementary anticodon) and to AA
How does the AA bind to tRNA?
Short, single-stranded 3’ region of tRNA ribose binds to carboxyl end of AA forming ester bond
What is the recognition and binding of correct AA dependent on?
Aminoacyl-tRNA synthetase
Covalently couples each AA to appropriate tRNA molecule
How are ribosomes formed?
Ribosomal proteins synthesised in cytoplasm, transported back to nucleolus to bind with rRNA subunit and exported back to cytoplasm
Describe the structure of ribosomes
1 small subunit, 1 large subunit
Small: provides framework on which tRNA anticodons accurately matched to mRNA codons
Large: catalyses formation of peptide bonds linking AAs
What is the function of ribosomes?
Maintain the correct reading frame and ensure accuracy
What are the 4 binding sites of ribosomes?
- mRNA
- Aminoacyl (A): tRNA with bound AA
- Peptidyl (P): tRNA attached to growing peptide chain
- Exit (E)
Describe the process of protein synthesis
- Ribosome subunit join near 5’ end of mRNA
- tRNA anticodon binds to complementary mRNA codon at A site bringing AA
- Ribosome moves towards 3’ end, at P site peptide bond forms between existing polypeptide and new AA
- mRNA moves 1 codon along through small subunit, tRNA ejected at E site, A site free again
What is the start codon of protein synthesis?
AUG which special tRNA binds to with methionine - distinct from usually methionine tRNA
What is the importance of the start codon?
Dictates reading frame for whole protein
Error can lead to frame shift mutation where reading frame is shifted causing all codons to be translated incorrectly forming non-functional protein
What are the stop codons and how do they work?
UAA, UAG, UGA
Signal binding of release factor
Forces peptidyl transferase to bind water freeing carboxyl end of peptide that keeps peptide in ribosome
Released into cytoplasm
Define somatic and reproductive division
Somatic: cells of body reproduce themselves
Reproductive: body produces gametes
What is the function of somatic division?
Process by which body grows and replaces dead/damaged cells
What is the feel cycle?
Orderly sequence of events in which the cell: duplicates its contents, divides
Why must contents must be duplicated for the CC?
So genes can be passed onto next generation
What are the 2 major phases of the CC?
Interphase: not diving
Mitotic phase: diving
What is interphase?
State of high metabolic activity during which cell does much frowning and replicates DNA and organelles/proteins
What are the 3 stages of interphase and state what happens during them
G1: replicates organelles and cytosol
S: DNA replication
G2: enlarges, synthesises enzymes and proteins for mitosis
What is the G0 phase?
Phase most cells are in
If exit cell cycle enter G0, usually cannot re-enter
What are the 2 stages of the mitotic phase?
Mitosis: nuclear division
Cytokinesis: cell division
What are the 4 phases of mitosis and what happens during each?
Prophase: chromatin condense to paired chromatids, nucleolus and nuclear membrane disappear, centrioles move to opp. poles
Metaphase: chromatids line up on metaphase plate
Anaphase: identical sets of chromosomes move to opp. poles
Telophase: nuclear envelope and nucleoli re-appear, chromosomes resume chromatin form
When does cytokinesis occur and what happens?
In late anaphase
Contractile ring forms cleavage furrow around centre of cell
Cytoplasm divided into 2 equal portions
What are cyclins and Cdks?
Cyclins are regulatory proteins that activate Cdks
Rb tumour suppressor gene is the major target of Cdks which they phosphorylate at multiple points throughout CC
What is meant by G1 restriction point being the ‘point of no return’?
Once cell proceeds through point it will complete CC including mitosis and cytokinesis
How can inhibitors block the CC?
Inhibitors of Cdk4 (INK4 protein) can prevent phosphorylation of Rb
Define hypertrophy and give examples of chronic hypertrophy
Increase in size of cell without division
Cirrhosis of liver: hepatocytes become swollen causing narrowing of sinusoids
Heart conditions: cardiac myocytes hypertrophy in response to excessive workload
What is atrophy?
Decrease in size/number of cells and subsequent decrease in size of tissue/organ
Cachexia seen in HIV and cancers
Define hyperplasia and give example of chronic
Increase in no of cells due to inc. in cell division
Psoriasis in skin
Make prostate may lead to benign or malignant tumour
What is a cancer?
Cells that divide without control
Usually associated with loss of tissue differentiation and function (anaplasia)
What are tumours?
Swelling or lesion formed by abnormal cells
May be cancerous (malignant) and usually spread to other organs (metastasis)
How does epidermal growth factor regulate cyclin D1 production?
- EGF binds receptor, activates G protein
- kinase cascade will phosphorylate AP1 transcription factor through jun subunit
- TF binds promoter region of cyclin D1 causing transcription of cyclin D1
Define glycolysis
Breakdown of glucose to 2 pyruvate and ATP molecules
Define glycogenesis
Assembly of glycogen from excess glucose
Requires ATP, initiated by insulin
Define glycogenolysis
Breakdown of glycogen to glucose
Regulated by glucagon
Define gluconeogenesis
Synthesis of glucose from metabolites (lactate, pyruvate, glycerol, alanine)
What are Islets of Langerhans?
Highly vascularised endocrine glands in the pancreas
High vascularisation allows hormones ready access to circulation
What are the 4 secretory cells of the Islets?
a: glucagon
B: insulin
Delta
Digamma
What are the functions of insulin?
Regulate blood glucose: signals liver, muscles, adipose to take up glucose; aides cells taking up for energy
Signal storage of Glc as Gly when in excess
Describe the synthesis of insulin
- Leader sequence cleaved leaving proinsulin made of A,B,C domains
- Proteases cleave proinsulin in 2 places releasing peptide C and mature insulin (A,B joined by S-S bond)
- Packaged into secretory granules containing equimolar amounts of insulin and peptide C
- Released into extracellular space during secretion
Describe the 7 steps of insulin release
- Glc enters via GLUT2
- Inc. influx inc. Glc metabolism, inc. [ATP]i
- Inc. [ATP]i inhib. KATP channel
- Closed KATP causes depolarisation
- Depolarisation activates VGCa2+C in PM
- Influx of Ca2+, inc. Ca2+ induces Ca2+-induced Ca2+ release
- Ca2+ leads to exocytosis, releasing secretory granules
What are the 3 chemical controls of insulin release?
AAs: stim. (inc. uptake and protein synthesis)
Keto acids: stim. (inc. uptake to prevent lipid and protein utilisation)
Glucose: stim. (feedback loop)
What hormones are B cells sensitive to?
Glucagon - inhib.
Somatostatin - inhib
Describe the neuronal control of insulin release
PSNS: ACh stim
SNS: NA inhib
Describe the stim. of Glc disposal postprandial
Insulin binds receptor
Insulin signalling pathway activates: effects on protein metabolism, effects on growth, effects on lipid metabolism and translocation of GLUT4 containing vesicles to PM
Inc. Glc uptake
Describe the inhib. of Glc production postprandial
Insulin blocks Glc production via glycogenolysis and gluconeogenesis
PEPCK (inhib gluconeogenesis) and glycogen phosphorylase both targeted
Can be acute (dephosphorylation of phosphorylase) or long-term (suppression of PEPCK gene expression)
Describe the effects of insulin on adipocyte lipid metabolism
Stim: lipoprotein lipase (LPL), FA uptake, triglyceride esterification
Inhib: adipose TAG lipolysis preventing release of FA and glycerol
What are the functions of glucagon?
Stim. glycogenolysis
Stim. gluconeogenesis
Stim. lipolysis
Describe how glucagon is regulated
Inc. Glc inhib. release
AAs stim. release
Stress: AD acts on B receptors on a cells stim. release
Insulin inhib. glucagon release
How does glucagon stimulate hepatic Glc production?
Stim. gluconeogenesis and glycogenolysis
Describe the effects on insulin and glucagon on hepatic lipid homeostasis during fasting
Insulin: suppresses lipin-1 red. VLDL production, carnitine palmitoyltransferase 1 (CPT1) thus inhib. ketogenesis
Glucagon: opposite effects thus inc. VLDL production and stim. ketogenesis
What is the structure of glycogen?
Polymer of glucose residues linked a(1,4) between molecules and a(1,6) at branching points
What does glycogen phosphorylase catalyse?
Gly(n residues) + Pi -> gly(n-1 residues) + glc-1P
Catalyses phosphorolytic cleavage of a(1,4) glycosidic linkages
Glc-1P released as product
What is the prosthetic group for GP?
Pyridoxal phosphate (PLP) Phosphate used to break bond
What is the function of phosphoglucomutase?
Catalyse glc-1P -> glc-6P
Glc-6P either enter glycolysis or dephosphorylated for release to blood
Free energy = 0, reaction dependent on conc.
Explain how glycogen debranching enzyme work
When 4 residues left glycogen phosphorylase stops
a(1,4) transglycosylase transfers 3 residues into linear chain
a(1,6) glucosidase removes remaining glc
Describe liver glycogenolysis and its importance
Glc-6Pase coverts glc-6P to glc
Liver gly converted to glc due to presence of glc-6Pase
Substitutes for gut during initial stage of starvation as liver glycogen results in direct release of glucose
Describe skeletal muscle glycogenolysis
Lack glc-6Pase so glc-6P enters glycolysis
Glycogenolysis generates ATP for contraction
Lactate generated transported in blood to liver, precursor for gluconeogenesis
What are the 2 steps of glycogen synthesis?
Formation of UDP-glc
Glycogen synthesis
Describe the formation of UDP-glc
From glc-1P
Glc-1P + UTP -> UDP-glc + PPi
PPi + H20 -> 2Pi
Overall: Glc-1P + UTP -> UDO-glc + 2Pi
Spontaneous hydrolysis of P bond in PPi drives reaction
Cleavage of PPi only energy cost in glycogenesis
Describe glycogen synthesis
Glycogen synthase catalyses
Gly(n residues) + UDP-glc -> gly(n+1 residue) + UDP
Catalyses transfer of glc to OH C4 of terminal residue of gly chain forming a(1,4)
Branching enzyme transfers segment from end of gly to OH C6 of glc residue of gly forming a(1,6) 4 residues from existing branch
How is glycogenesis regulated?
Modification 1 (phosphorylase) Phosphorylase b (less active) phosphorylated to phosphorylase a (more active) which inhib. glycogenesis Dephosphorylated by phosphoprotein phosphatase-1
Modification 2 (glycogen synthase) GS a (active) phosphorylated to GS b (inactive) inhib. glycogenesis Dephosphorylated by phosphoprotein phosphatase-1
Explain how cAMP controls glycogenesis
Glucagon and NA inc. cAMP levels, activates PKA
PKA phosphorylates GS to inactive form - inhib. glycogenesis
PKA phosphorylates phosphorylase kinase (active) which phosphorylates GP (active) inhib. glycogenesis (enhance glycogenolysis)
Insulin inhib. cAMP suppressing glycogenolysis
Describe insulin control of glycogenesis
Insulin activates GS phosphatase which dephosphorylates GS (active)
Glycogenesis occurs
GS kinase 3 and cAMP phosphorylate (inactive) GS, insulin suppresses GSK3, cAMP enhancing glycogenesis
What is gluconeogenesis?
Synthesis of glc from non-carb C substrates - lactate, pyruvate, glycerol, glycogenic AAs
What is the importance of gluconeogenesis?
During fasting liver glycogen is depleted
Gluconeogenesis is source of glucose during this
Requires energy and C source
What are the 2 important enzymes of gluconeogenesis and where are they found?
Pyruvate carboxylate - mitochondria
Glc-6Pase - ER
What is the role of pyruvate carboxylase?
Catalyse pyruvate to oxaloacetate
Allosterically activated by acetyl-CoA
[oxaloacetate] limiting factor for Krebs cycle
In active gluconeogenesis oxaloacetate diverted to form glc, inc. [acetyl-CoA] activates pyruvate carboxylase
Outline the steps of gluconeogenesis
Opposite of glycolysis with 4 differences
- PC: pyruvate -> oxaloacetate
- PEPCK: oxaloacetate -> phosphoenolpyruvate
- Enolase: PEP -> 2-phosphoglycerate
- Phosphoglycerate mutase: 2-phosphoglycerate -> 3-phosphoglycerate
- Phosphoglycerate kinase: 3-phosphoglycerate -> 1,3-bisphosphoglycerate
- Glyceraldehyde-3P Dehydrogenase: 1,3-bisphosphoglycerate -> glyceraldehyde-3P
- Triosphosphate isomerase: glyceraldehyde-3P dihydroxyacetate-P
- Aldolase: glyceraldehyde-3P + dihydroxyacetate-P -> fructose-1,6-bisP
- Fructose-1,6-bisPase: fructose-1,6-bisP -> fructose-6P
- Phosphoglucose isomerase: fructose-6P -> glucose-6P
- Glc-6Pase: glucose-6P -> glucose
How is the pyruvate kinase reaction of glycolysis reversed in gluconeogenesis?
Using pyruvate carboxylase, malate dehydrogenase, PEP carboxykinase
Pyruvate enters mitochondria and converted to oxaloacetate by PC
MDH catalyses oxaloacetate to malate
Malate exits mitochondria converted to oxaloacetate (enters gluconeogenesis)
Oxaloacetate converted to PEP by PEPCK and continues gluconeogenesis
How is gluconeogenesis regulated?
Glc-6Pase: [Glc-6P]
Fructose-1,6-bisPase: AMP, fructose-1,6-bishop (inhib)
PC: acetyl-CoA (enhance)
Describe the effect of glucagon-cAMP cascade in the liver
Gluconeogenesis stim
Glycolysis inhib
Glycogenesis inhib
Glycogenolysis stim
Free glc released to blood
Explain how glucose/glycogen can be a C source for gluconeogenesis
Glycolysis forms lactate which is converted to pyruvate by lactate dehydrogenase
Explain how proteins can be a C source for gluconeogenesis
Proteolysis forms AAs which are broken down to pyruvate
All AAs except lysine and leucine can supply C
Explain how triglyceride can be a C and ATP source
Lipolysis produces glycerol and FAs
Glycerol enters hepatic gluconeogenesis
FAs oxidised releasing ATP, acetyl-CoA, NADH
Acetyl-CoA and NADH inhib. pyruvate dehydrogenase enzyme (prevents loss of CO2, more pyruvate for gluconeogenesis)
Acetyl-CoA enhances PC (more oxaloacetate)
Outline the 8 steps of the TCA cycle
Can I Keep Selling Sex For Money Officer?
CAIK Sounds So Fucking Mint
Citrate Isocitrate a-ketoglutarate Succinyl-CoA Succinate Fumarate Malate Oxaloacetate
Citrate synthase Aconitase Isocitrate dehydrogenase a-ketoglutarate dehydrogenase Succinyl-CoA synthase Succinate dehydrogenase Fumarase Malate dehydrogenase
What step of TCA is substrate level phosphorylation?
Succinyl-CoA synthase: Succinyl-CoA succinate
GDP -> GTP
What are the products of TCA per glucose?
6 NADH2
2 FADH
2 GTP
What 3 subunits make pyruvate dehydrogenase enzyme?
- Pyruvate carboxylase
- Lipoamide reductase transacetylase
- Dihydrolipoyl dehydrogenase
What are the 3 conditions and fates of acetyl-CoA?
- Presence of carbs and energy used: metabolised to CO2, NADH, FADH2, GTP - all eventually ATP
- No energy use: made into fat
- Energy, no carbs: ketone bodies
What 2 steps of TCA are endergonic?
Aconitase: citrate isocitrate
Malate dehydrogenase: malate oxaloacetate
What are the 2 regulatory steps in TCA?
Isocitrate dehydrogenase
a-ketoglutarate dehydrogenase
What factors stimulate and inhibit the 2 regulatory dehydrogenases?
- Inc. [ATP/NADH] inhibits
2. Ca2+ stimulates
In the fed state what is the biosynthetic role of TCA?
Excess glucose converted to acetyl-CoA then citrate which is exported from mitochondria
ATP and citrate lyase convert citrate to acetyl-CoA and oxaloacetate
Acetyl-CoA then enters lipogenic acid and cholesterol synthesis pathways to forms FAs and cholesterol
What is the biosynthetic role of TCA in the fasted state?
AAs that can be converted to oxaloacetate yield net glucose synthesis
FAs can’t be converted as C atoms from acetyl-CoA lost as CO2
Acetyl-CoA can’t be converted to pyruvate as reaction irreversible
How does FA oxidation block glucose oxidation?
Acetyl-CoA and NADH (produced by FAO) are inhibitors of PDC which converts pyruvate to acetyl-CoA
Acetyl-CoA and NADH stimulate PDC kinase to phosphorylate PDC to inactive form
What happens to citrate when glucose is ample?
Exported from mitochondria and converted to acetyl-CoA then malonyl-CoA (FA synthesis precursor)
Rise in malonyl-CoA inhibits COR-1 and suppresses FAO
How do hypoxic events upregulate glycolysis?
Hypoxia-inducible factor (HIF1) transcription factor is stabilised, bind to hypoxia responsive elements in promoter regions including glycolytic enzymes
How does chronic HIF action low mitochondrial respiration?
HIF1 downregulates mitochondrial respiration by promoting mitochondria autophagy and suppressing mitochondrial biogenesis
May be adaptive mechanism to prevent oxidative stress by restricting production of reactive oxygen species
Defined glucogenic and ketogenic
Glucogenic: glucose can be formed from C skeleton
Ketogenic: AAs degraded to acetyl-CoA
What are the 10 essential AAs?
PVT TIM HALL
Phenylalanine
Valine
Tryptophan
Threonine
Isoleucine
Methionine
Histidine
Arginine
Leucine
Lysine
Give an overview of AA metabolism
Ingested protein, biosynthesis and degraded proteins produce AAs
AAs produce proteins, purines, pyrimidines, porphyrins
Degraded to C skeleton and N
N excreted in urea
C skeletons to ketogenic/glucogenic products
What are the 3 steps to AA degradation?
NH2 group removed
Detoxification of amino group
Metabolism of C skeleton
Outline the urea cycle
Ammonia converted to carbamoyl phosphate which reacts with ornithine to form citruline
Citruline converted to arginino-succinate by argininosuccinate synthase and broken down to arginine by argininosuccinate lyase
Arginine converted to ornithine releasing urea by arginase
What are the general effects of insulin?
Start Glucose uptake in muscle, adipose Glycolysis Glycogen synthesis Protein synthesis Uptake of ions
Stop Gluconeogenesis Glycogenolysis Lipolysis Ketogenesis Proteolysis
Compare regulation of blood glucose in fed and fasting states
Fed: insulin secreted by beta cells, stimulates synthesis of metabolic fuel store, lower glucose level
Fasting: glucagon secrete by alpha cells, stimulates mobilisation of metabolic fuel store, raises glucose
Describe diabetes mellitus
Common endocrine disorder characterised by hyperglycaemia due to defects in insulin production, an absolute or relative lack of insulin or cell resistance to insulin
What are the 2 main types of diabetes?
- Insulin dependent DM/Type 1: IDDM
2. Non-insulin dependent DM/Type 2: NIDDM
What is secondary diabetes mellitus?
Diabetes that arises as consequence of another condition
How may secondary diabetes arise?
Pancreatic disease
Endocrine disease
Drug therapy
Insulin receptor abnormality
Describe T1 diabetes
Can occur at any age, most common in young
Autoimmune destruction of beta cells cause absolute lack of insulin
Viral infections may be possible precipitating factor
Can be predicted by presence of Islet cell antibody presence in serum
Describe T2 diabetes
Occur any age, most common 40-80yo
Resistance of tissues to action of insulin, insulin levels normal to high
Commonly associated w/ obesity
What is type 3 diabetes?
Gestational diabetes
Occurs in 3-10% pregnancies
Describe T3 diabetes
Non-diabetics exhibit high blood glucose during pregnancy
Presence of human placental lactogen interferes w/ susceptible insulin receptors causing them to not function properly
What are the risks associated w/ T3 diabetes?
Being large for gestational age, low blood sugar, jaundice (in child)
Unmanaged: develop T2, higher incidence of pre-eclampsia, C-section
Children: obesity and T2 diabetes
What predisposing factors are associated w/ T1 diabetes?
Interplay of 3 leading to selective destruction of beta cells
- Genetic
- Environmental: diet, toxins, viral
- Autoimmune: presence of islet antibodies
What predisposing factors are associated w/ T2 diabetes?
Complex genetic interactions modified by environmental
Genetic: familia aggregation, susceptibility genes
Obesity, physical inactivity, stress
Adipocyte-derived hormones and cytokines, metabolically active hormones may affect insulin sensitivity
What 6 symptoms are associated w/ hyperglycaemia?
- Polyuria
- Polydipsia
- Lassitude
- Weight loss
- Polyphagia
- Blurred vision
What complications are associated w/ diabetes?
Leading cause of death and early disability
Inc. risk of cardiac, cerebral, peripheral vascular disease
Altered hand/foot sensation
Inc. risk of periodontal disease
What are the acute compilations of diabetes?
- Hyperglycaemia
- Diabetic ketoacidosis
- Hyperglycaemic hyperosmolar non-ketotic coma
What are 5 chronic complications of diabetes?
- Microangiopathy: small blood vessels
- Macroangiopathy: large blood vessels
- Neuropathy:
- Retinopathy: blindness
- Nephropathy: kidney failure
What are the 3 main tests for diabetes?
- Random blood sample
- Fasting blood sample
- Oral glucose tolerance test
For random blood glucose, at what level would diabetes be diagnosed?
> /= 11.1 mmol/L
For fasting sample what levels of glucose are deemed non-diabetic, impaired fasting glycemic and diabetic?
Non: <6.0
Impaired: 6.1-6.9
Diabetic: >7.0
For oral glucose test what glucose levels for fasting and 2 hours later are deemed impaired glucose tolerance and diabetic?
Fasting: impaired <7.0, diabetic >/=7.0
2 hour: impaired 7.8-11.0, diabetic >/=11.1
Why is HbA1c assessment preferred in monitoring diabetes?
More reliable and accurate assessment of long term control as represent long term blood glucose level during lifetime of protein
What is glycation?
Irreversible, enzymatic attachment of glucose to proteins
What is HbA1c count?
Measurement of average blood glucose level during preceding 60-90 days before testing
Measured as % of total haemoglobin conc.
What is a good HbA1c count?
7%
What are the 4 predisposing factors of diabetic ketoacidosis?
All in/direct result of lack of insulin
- Infection
- Myocardial infarction
- Trauma
- Omission of insulin
What happens in the absence of insulin?
Muscle and adipose breakdown triglycerides to produce FAs as alternative energy source
Inc. lipolysis leads to overproduction of FAs, converted into ketones can cause ketonaemia, metabolic acidosis, ketonuria
What happens as glucose transport into tissues decreases?
Hyperglycaemia leading to glycosuria resulting in osmotic diuresis causing loss of water and electrolytes
Will result in severe dehydration, cause pre-renal uraemia and may lead to hypovolaemic shock
What is the clinical relevance of diabetes?
How will treatment subsequently affect eating: will it lead to hypoglycaemia?
Collapsing
Hyperglycaemia: loss of consciousness but long process from onset of symptoms to loss of consciousness
Hypoglycaemia: may be evident within mins, rapidly lead to loss of consciousness or develop gradually and lead to profession of alteration in consciousness
What is a counter regulatory hormone?
A hormone that opposes affect of another hormone i.e. an antagonist
What are the 4 main insulin CRHs and what do they respond to?
- Glucagon
- AD
- Cortisol
- Growth hormone
Respond to hypoglycaemia
What are the 3 methods for non-diabetic control of hypoglycaemia?
- Pancreas reduce insulin secretion
- Alpha cells secrete glucagon, liver release more glucose
- Adrenal glands secrete AD; liver and kidneys produce more glucose
prevents tissues using glucose from bloodstream
red. insulin secretion
What happens if glucagon and AD fail to return glucose levels to normal?
hGH and cortisol will raise glucose
What is the function of hGH?
Childhood: regulate growth rate
Adult: maintain muscle and bone mass, tissue repair and healing
Secreted by somatotrophs
Main function is to stimulation production of insulin-like growth factor by cells in liver, skeletal muscle, cartilage, bone
What is the function of ILGF?
Stimulate release of glucose into blood by liver
What do hypoglycaemia and hyperglycaemia stimulate the hypothalamus to release?
Hypo: GH-releasing hormone
Hyper: GH-inhibiting hormone
What are the sections of the adrenal glands?
Cortex: outer 80%
Medulla: inner 20%
Describe the adrenal cortex
Many LDL receptors
Enable cholesterol uptake for steroid hormone synthesis
Secrete: glucocorticoids (cortisol), mineralcorticoids (aldosterone), androgens
Describe the adrenal medulla
Secrete: catecholamine hormones (NA, AD) and dopamine
Describe cortisol
Secreted in response to ACTH from pituitary
-ve feedback loop
Describe aldosterone
Stimulated by inc. K+ plasma
Regulates electrolyte balance
Describe androgens
Steroid hormones that have masculinising effects
What are the 3 hormone systems of the adrenal glands?
- Glucocorticoids (cortisol)
- Mineralcorticoids (aldosterone)
- Androgens
What is adrenocorticotrophic hormone?
Regulatory hormone secreted by corticotrophs in ant. pituitary
Controls production and secretion of cortisol/glucocorticoids by adrenal cortex
Stimulated by CRH from hypothalamus, stress stimuli (trauma, blood glucose) and interleukin-1 from macrophages
Describe the action of glucocorticoids/cortisol
Binds to cytosolic receptor and translocated to nucleus upon activation
Regulates BP and suppresses inflammation
Enhances: gluconeogenesis, adipose tissue lipolysis, muscle proteolysis
Inhib: glucose utilisation
Describe catecholamine action
Release in response to stress
Characterised by inc. O2 consumption and hypermetabolism
AD stim: glycogenolysis in liver and muscle; gluconeogenesis in liver
Stim: adipose alternative fuel cells to glucose
Inc. HR
Describe hypofunction of the adrenal glands
Adrenal insufficiency; rare, potentially fatal
Signs: lethargy, anorexia, low BP, hypoglycaemia, hyperpigmentation
Life threatening Na depletion and possible K retention due to aldosterone deficiency causing low BP
Therapy: Na maintenance, hormone replacement
What is hyperfunction of adrenal cortex?
Overproduction of cortisol, androgens and aldosterone
Prolonged, excessive exposure can lead to Cushing’s syndrome
What is Cushing’s syndrome?
When ACTH levels don’t respond to -ve feedback from high cortisol levels
Characterised by remodelling of adipose tissue: deposition on face and trunk, loss from limbs
Wasting of skeletal muscle, osteoporosis, slow healing, thinning of skin
Excess cortisol may lead to diabetes and hypertension
What are tetraiodothryonine and triiodothyronine?
Thyroid hormones 4 and 3
Are thryonines w/ 3/4 iodine atoms
Regulated by controlling conversion of 4 to 3 (active from) in target tissues (liver, kidney)
Described the mechanism of thyrothropin releasing hormone and thyroid stimulating hormone
TRH controls TSH release
TSH stimulates production and secretion of T3 and 4 by thyroid
T3and4 control release of TRH
What are the 9 general metabolic effects of thyroid hormones?
Inc: basal metabolic rate, body temp, glucose and FA use for ATP synthesis, glucose uptake, lipid and protein turnover
Stim: protein synthesis, lipolysis, synthesis of Na/K ATPase
Effect on gene expression: slow, long lasting
Regulate development and growth of nervous tissue and bones
What are the 8 clinical features of hypothyroidism (myxoedema)?
- Lethargy, tiredness
- Weight gain
- Apathy
- Slow pulse
- Cold intolerance
- Constipation
- Myxoedema
- Elevated serum TSH
What are the 7 clinical features of hyperthyroidism (thyrotoxicosis)?
- Hyperactivity, insomnia
- Weight gain
- Diarrhoea
- Palpitation
- Heat intolerance
- Suppressed TSH, elevated T4
- Agitation
What is body mass index?
Universally accepted classification of obesity
Person’s weight (kg) in relation to height (m)
What are the BMIs for normal, over weight and the 3 classes of obesity?
Normal: 18.5-24.9 Overweight: 25.0-29.9 Class I: 30.0-34.9 Class II: 35.0-39.9 Class III: >40.0
Describe the co-morbidity risk changes as weight inc.
Normal: no inc. Overweight: inc. Class I: moderate inc. Class II: severe inc. Class III: v severe inc.
Discuss the advantages of BMI
Low-cost, easy to use
Commonly used to determine healthy weight, can compare weight to GP
Correlates well w/ amount body fat measured by complex techniques
Predicts dangers; as BMI inc. risk inc.
Useful screening tool to use @ popn. level, as universally used lots of data from many popns.
What is the disadvantage of BMI?
Fails to distinguish between fat and muscle
What is obesity?
Excessive accumulation of fat
What 2 methods can be used to assess obesity?
- Waist circumference
2. Waist-hip ratio
Describe waist circumference
Taken at level of iliac crest
Men: >40” health risk
Women: >35” health risk
Describe waist-hip ratio
Waist circumference @ level of L3 over hip circumference @ largest gluteal region
Men: >1.0
Women: >0.85
Describe the changes in epidemiology and prevalence of obesity
WHO says it is now an epidemic
In last 10yrs inc. by 10-40% in most European countries
Describe prevalence of obesity in Britain
Now has highest obesity rate of all Western European counties: 50% overweight, 20% obese
> 1.1billion adults overweight, 312mil clinically obese
10% children overweight/obese, 17.6mil <5 overweight
What are the 4 main factors for cause of obesity?
- Genes
- Socio-economic: diet and lifestyle
- Cultural
- Psychological and medical
What is the evidence for genes playing a role in obesity?
Adults who were adopted as children have weight closer to biological parents
Monozygotic twins show much stronger correlation in weight than dizygotic twins
Describe the socio-economic factors in obesity
Diet
Inc. energy dense foods: animal fats
Dec. complex carbs: fibres, coarse grains
Inc. alcohol, salt
Lifestyle Affluent life w/ less physical activity Car: drive instead of walk TV/games: long time sitting/watching Energy/time saving devices: red. manual labour in home
How do cultural factors play a role in obesity?
In some countries big is attractive and sign of health and prosperity
Describe the psychological and medical factors contributing obesity
Psychological: eat in response to -ve emotions; sadness, anger, boredom
Conditions: depression, hypothyroidism, chromosomal anomalies
Drugs: corticosteroids, antidepressants, antipsychotics, B-blockers, oral contraceptive, oral hypoglycaemic agents, insulin, antihistamines
What are the 9 possible effects of obesity?
- Hypertension
- Stroke
- T2 diabetes
- Cancer: endometrium, breast, prostate, colon
- CV mortality
- Respiratory diseases, sleep-apnea
- Osteoarthritis
- Gallbladder disease
- Metabolic syndrome
What are the 2 main types of obesity?
- Intra-abdominal/visceral
2. Lower body/external
What are the 6 main CV diseases associated with obesity?
- Hypertension
- Atherosclerosis
- L ventricle hypertrophy
- Cardiac necrosis
- Cardiac arrhythmias
- Heart attack
How does obesity cause hypertension?
Inc. body mass associated w/:
Inc. blood vol. and viscosity
Inc. angiotensinogen release from adipocytes
Inc. cholesterol and BP
What effect does atherosclerosis have on the heart?
Inc. workload
What affect does inc. workload have on the heart?
L ventricle hypertrophy
What happens when heart workload continues to inc.?
Coronary arteries unable to sustain heart
Ischaemia: lack of blood
Unable to manifest during high demand
Heart loses elasticity: unable to relax completely, dec. filling, dec. blood pumped around body
What is congestive heart failure?
Inability of heart to contract properly
Explain how obesity can lead to T2 diabetes
Insulin secreted in response to intake of food
Prolonged periods of food intake causes constant production of insulin
Cellular insulin receptors are down regulated leading to insulin resistance
High levels of FAs and glucose in blood
Depletion of glucose reserves as glucose not transported
Person feels hungry and eats more
What are the 5 methods of treatment of obesity?
- Dietary modifications
- Behavioural modifications
- Physical activity
- Pharmacological
- Surgery
Describe dietary modifications for the treatment of obesity
Nutritionally balanced, low calorie
Inc.: fruit, veg, whole grains, nuts
Dec.: fatty, sugary foods
Describe some behavioural modifications to treat obesity
Keep food diary: time, place, activity, emotions; find link to period of eating/inactivity
Help to avoid eating when in feet, watching TV, playing games etc
Encouraged to eat home cooked meals and walk rather than use car
When should pharmacological treatment of obesity be considered?
18-75yrs: BMI >30
BMI >27 w/ pre-existing risk factor: hypertension, diabetes, obstructive sleep apnoea, cardiac disease
BMI >30 and 3 months care not red. weight
What 2 drugs are licensed to be used in treatment of obesity?
- Orlistat
2. Sibutramine
Describe orlistat
Prevents fat digestion and absorption by binding to GI lipase
Useful for those w/ high fat diet
Describe sibutramine
Red. appetite and inc. thermogenesis
Useful for those who can’t control appetite
What must be taken into consideration when a patient is on pharmacological treatments of obesity?
Shouldn’t be sole therapy
Must be strictly and regularly monitored: discontinued if weight loss <5% after 12ws or weight gain recurs
Shouldn’t be on longer than year, never more than 2 years
Describe surgical treatment of obesity
Only in severe cases: BMI >40
2 accepted procedures: gastroplasty, gastric bypass
Both red. stomach to small pouch to limit amount of food that can be consumed
Describe vitamins
Class of organic compounds categorised as essential nutrient
Required for normal function, growth and maintenance
Essential for several enzymatic process in human metabolism
Are cofactors: don’t do anything themselves
What are the 2 classes of vitamins?
- Fat soluble: A D E K
2. Water soluble: B complexes, C
Describe water soluble vitamins
Source: fruits, vegs, grains, meat Absorption: directly into bloodstream Storage: circulating freely, not stored in body Excretion: excess in urine Toxicity: rare, possible w/ supplements
Describe fat soluble vitamins
Source: fats and oils in food Absorption: w/ lipids through lymphatic system Storage: in fat and liver Excretion: not easily excreted Toxicity: easily reached
Describe the sources, RDA and toxicity of vit A
Source: meat, liver, diary products Retinol - active form
yellow, red, green fruits and vegetables; Carotene - precursor
RDA
men: 0.7mg/day; women: 0.6mg/day
Toxicity: >1.5mg/day
Painful joint, anorexia and/or vomiting, liver damage, fatigue, loss of hair
What are the 4 functions of vit A?
- Promote vision: retinal needed in rhodopsin
- Protein synthesis and cell differentiation
- Reproduction and growth
- Bone growth remodelling
What are the 5 ocular and 3 extra-ocular effects of vit A deficiency?
Ocular
- Night blindness
- Conjunctival xerosis
- Bitot’s spots
- Corneal xerosis
- Keratomalacia
Extra-ocular
- Retarded growth
- Skin disorders
- Effect on bone
Describe Bitot’s spots, conjunctival xerosis and keratomalacia
Bitot’s spots: foamy whitish cheese-like tissue spots, cause severe dryness
Conjunctival xerosis: conjunctiva becomes dry and non-wettable, appears muddy and wrinkled
Keratomalacia: cornea becomes soft, may burst open, if eye collapses vision lost
What is carotenemia?
Impairment of conversion of carotene to Vit A due to inborn metabolic error or hepatic disease
Generalised yellowish skin and mucosa
Excessive deposition of carotene due to high intake of carotene containing foods
What are the 5 oral manifestations of vit A?
- Xerostomia
- Altered taste
- Gingival hypertrophy
- Dec. ameloblast and odontoblast formation
- Disrupted enamel formation, irregular tubular dentine formation
What is unique about Vit d?
Only fat soluble vitamin humans can synthesise
What are vit D3 and D2?
D3: cholecalciferol
D2: ergosterol
Describe the metabolic synthesis of vit D3
Cholesterol converted to 7-dehydrocholesterol
UV rays convert 7DC to cholecalciferol which is then hydrolysed in kidney and liver to active 1,25-dihydroxycholecalciferol
What are the dietary sources of vit D3?
Cheese Butter Margarine Fish Fortified milk and cereals
What are the RDAs for vit D?
Pregnant/breastfeeding/>65: 0.01mg/d
6m-5y: 0.007-0.0085mg/d
What are the 7 signs and 2 complications of vit D toxicity?
- Constipation
- Anorexia
- Fatigue
- Muscle weakness
- Irritability
- Vomiting
- Dehydration
Complications
- Kidney stones
- Kidney failure
What are the 5 functions of vit D?
- Ca and K balance
- Bone and tooth development: enhance Ca absorption in gut and renal tubules
- BP regulation
- Immunity
- Cell differentiation
What are the affects of vit D deficiency?
Rickets: dec. Ca, poor calcification, deformed bones
Osteomalacia: post-menopause, bone pain, weak muscle
Inc. risk of osteoporosis
What are the 4 oral manifestations of vit D deficiency?
- Teeth: developmental abnormalities in enamel and dentine
- Higher risk of caries
- Enamel hypoplasia
- Pulp: high horns, large chamber, delayed closure of root apices
What are the 2 types of vitK and their sources?
K1: plant; spinach, cabbage, broccoli, cauliflower, wheat germ, tomatoes, potatoes, carrots
K2: synthesised by intestinal bacteria from milk, fish, meat
What is the RDA for vitK?
0.001 mg/d per kg weight
What are the 2 functions of vitK?
- Production of blood clotting factors II, V, VII, IX, X
2. Bone mineralisation: VitK-dependent proteins; osteocalcin, matrix Gla protein, protein S role in matrix formation
What are the effects of vitK deficiency?
Inc. prothrombin time and risk of haemorrhage
Bone deformation
What is the oral manifestation of vitK deficiency?
Uncontrollable gingival/mucosal bleeding
What is VitE? Generally describe function and how it works
Family of 8 naturally occurring compounds
Powerful antioxidant, present in anti ageing products
Intercepts free radicals, prevents destruction of cell membrane
What are the sources of VitE?
Egg, fish, liver, butter
Soybean, palm oil, sunflower, corn, olive, nuts, green leafy veg, whole grain
What is the RDA for vitE?
Men: 4mg/d
Women: 3mg/d
What is the function of vitE?
Promote vasodilation
Inhibit platelet aggregation
Prevent atherosclerosis by preventing oxidation of LDLs
What are the effects of a VitE deficiency?
Premature ageing: hair, nails, skin
Inc. risk of CVD
Degenerative changes in blood capillaries
Name the B complex vitamins
B1: thiamin B2: riboflavin B3: niacin B5: pantothenic acid B6: pyridoxamine B12: cobalamin Biotin Folic acid
What are the sources of vitBs?
Yeast, grain, rice, fish, veg, meat
What is the effect of toxicity of B6?
> 5.0mg/d
Nerve damage, difficulty walking
Numbness in feet and hands
What are the 4 functions of vit Bs?
- Co-enzymes
- Energy metabolism: B1-6 and biotin
- RBC synthesis: folate, B12
- Homocysteine metabolism: folate, B6 and 12
What is the effect of B1 deficiency?
Beriberi: after 10 days
Weakness, nerve degeneration, irritability, poor leg/arm coordination, loss of nerve transmission
Oedema, enlarged heart, heart failure
Due to poor glucose metabolism
What is the effect of B2 deficiency?
Ariboflavinosis: occurs within 2 months
Glossitis, cheilosis, stomatitis, nervous system disorder
What does B3 deficiency cause?
Pellagra
Scaly sores, mucosal changes and mental syndrome
What does B6 deficiency result in?
Depression Nerve irritation Skin disorders Vomiting Impaired immune system
What does B12 deficiency cause?
Megaloblastic anaemia
Large and irregular RBCs
What oral manifestations do vit B deficiencies result in?
B2: glossitis, stomatitis, cheilosis
B12: aphthous ulcer
What are the sources of vitC in humans?
Citric fruits
What is the RDA for vit C?
40 mg/d
What 3 things does toxicity of vit C result in?
> 1000 mg/d
- Stomach pains
- Diarrhoea
- Flatulence
What are the 5 functions of vit C?
- Antioxidant
- Enhance iron absorption
- Synthesis of collagen
- Immune: reduce cold duration by 1 day
- Wound healing
What does vit C deficiency cause?
Scurvy: 20-40 day deficient
Fatigue, pinpoint haemorrhages
Bleeding gums and joints
What are the oral manifestations of vit C deficiency?
Loosening of teeth and tooth loss
Gum bleeding, gingivitis
What are the 3 most important trance minerals?
- Iodine: thyroid function
- Iron: haemoglobin
- Fluoride: bone and teeth
What are the 2 most important major minerals?
- Phosphorus: DNA
2. Calcium: bones
What are the 5 sources of fluoride?
- Toothpaste
- Fluoridated water
- Mouthwash
- Food processed w/ fluoridated water
- Fluoride supplements
What is the function of fluoride?
Anti-cariogenic:
prevent bacterial adhesion
suppress cariogenic bacteria
change enamel crystalline structure
Describe the changes in enamel crystalline structure due to fluoride
HA -> FA
Larger crystals
Higher pKa to dissolve
What is the result of fluoride toxicity?
Fluorosis
Chronic
Mottled enamel w/ scattered, irregular white flecks
Define inherited metabolic disorder
Metabolism disorder caused by mutation in gene that codes for enzyme resulting in enzyme deficiency and breakdown of metabolic pathway
What are the 6 clinical presentations in neonates of IEMs and 5 in young children?
- Vomiting
- Seizures
- Irritability
- Poor feeding
- Breathing disorder
- Abnormal tone
- Recurring vomiting
- Dysmorphic features: characteristic facial expression
- Mental retardation
- Seizures
- Developmental delay: milestones
What are the 7 categories of IEMs?
- AA metabolism disorders
- Carbohydrate metabolism disorders
- FAO disorders
- Lysosomal storage disorders
- Peroxisomal disorders
- Urea cycle disorders
- Mitochondrial disorders
What is Von Gierke’s disease?
IEM characterised by deficiency of glucose-6-phosphatase
Renders glycogen stores of body inaccessible
Lack free glucose
Glucose synthesis from glucose-6-phosphate via gluconeogenesis hampered
What are the affects of Von Gierke’s disease?
- Hypoglycaemia
- Lactic acidosis
- Hepatomegaly
Describe galactosaemia
Deficiency of galactose-1P uridyltransferase
Converts galactose-1P to glucose-1P which is subsequently converted to 6P and enters glycolysis
What are the effects of galactosaemia?
Child unable to utilise galactose component of lactose in milk
Accumulation of galactose-1P in blood, diarrhoea, vomiting, mental retardation, develop cataracts
What is the result of a deficiency of liver fructokinase or fructose-1P aldolase?
Fructokinase: convert fructose to fructose-1P
Fructose-1P aldolase: fructose-1P to glyceraldehyde
Fructose intolerance
Results in an accumulation of fructose-1P which inhibits both glycogenolysis and gluconeogenesis leading to hypoglycaemia
What are 2 AA metabolism disorders?
Alkaptonuria: black urine
Maple syrup urine disease
Describe alkaptonuria
Defect in breakdown of tyrosine and phenylalanine
Causes accumulation of homogentisic acid which is excreted in urine and oxidises on standing giving urine black colour
This can lead to arthritis due to build up in cartilage
Describe maple syrup urine disease
Defect in branched AA metabolism causing accumulation of keto-acids in urine
If left unmanaged can lead to physical and mental retardation
Describe phenylketonuria
Defect in phenylalanine hydroxylase causes impaired conversion of phenylalanine to tyrosine
Phenylalanine accumulates in blood and excreted in urine (aminoaciduria)
What are the signs of phenylketonuria?
Irritability
Vomiting
Mental retardation
Red. melanin formation
What are the 6 presentations of phenylketonuria?
- Mental retardation
- Hypopigmentation
- Developmental delay
- Musty odour
- Autism
- Epilepsy
What is familial hypercholesterolaemia?
Disorder caused by red. number functional LDL receptors in liver
What are the 3 effects of hypercholesterolaemia and treatment options?
- Premature coronary heart disease
- Tendon xanthomas
- Severe hypercholesterolaemia
Modify diet, fibrates, statins, bile acid binding resins
