ESA1 Flashcards
Define energy
The capacity to do work
List the 9 essential amino acids that are required in the diet
Isoleucine, lysine, threonine, histidine, leucine, methionine, phenylalanine, tryptophan, valine
How is ATP stored for short term use in skeletal muscle?
Creatine + ATP -> phosphocreatine + ADP by enzyme ‘creatine kinase’
Reversed at times of need
Creatinine is a useful marker of GFR, what is it a breakdown product of?
Creatine and phosphocreatine
Breakdown at constant rate, proportional to musle mass
Algorithms to fix for race etc.
Why is fat important in the diet?
Vit ADEK are fat soluble so need fat
Storage of energy
Some fatty acids cannot be synthesised, e.g. Linoleic and linolenic acids
Briefly outline glycolysis
C6 -> (+2ATPs) -> p-C6-p -> C3 -> 2NADH, FADH2, 4ATP, 2C3 (pyruvate)
Intracellular process, takes place in cytosol
Include link reaction?
Important intermediates of glycolysis?
Glycerol phosphate (made from DHAP via glycerol-3-phosphate dehydrogenase) Important in liver and adipose as needed for lipid synthesis
And 2,3-BPG (made from 1,3-BPG by enzyme bisphosphoglycerate mutase); important regulator of O2 affinity in RBC
Structure (big to small) and Features of skeletal muscle
Attached to bone via tendon
Fascia enveloping muscle
Epimysium enveloping bundles of fascicles
Perimysium enveloping one fascicle, containing nerves and blood vessels and muscle fibrils all travelling in parallel.
Endomysium surrounds muscle fibril, which consists of myofilaments
Peripherally displaced nuclei, striations, fused cells (mesodermally derived multipotent myogenic cells fused together).
Features of cardiac muscle
Branching Central nuclei Intercalated disks Desmosomes rivet cells together Gap junctions electrically couple cells
How can creatine kinase be used to assess a patient with suspected MI?
Specific isoform of creatine kinase, (CK-MM 70%; CK-MB 30%), released by damaged myocytes few hours after MI
Describe structure of alpha helix
Secondary structure 3.6 aa per turn 0.54 nm pitch Right handed helix NH group on one residue hydrogen bonds to C=O group 4 residues away
Describe structure of beta pleated sheet
0.35nm distance between adjacent amino acids
Parallel or antiparallel
How are amyloid fibres made
Usually soluble protein misfolded (beta sheet folded first) and becomes insoluble
Aggregates
Describe structure of collagen
Triple helix
Repeat of Gly-X-Y
Hydrogen bonds stabilise chains
Collagen fibrils formed from covalently cross-linking chains
Why does vitamin c deficiency result in scurvy?
Vit C is a co-factor for enzymes, prolyl hydroxylase and lysyl hydroxylase.
These enzymes hydroxylate proline (to hydroxyproline) and lysine (to hydroxylysine) in formation of procollagen.
This allows the cross linking that stabilises the triple helical structure
Sickle cell anaemia facts. Go.
Glu6 -> Val6
Valine is hydrophobic
Deoxyhaemoglobin therefore polymerise
More prone to lysis, because boomerang shape, and more rigid hence block microvasculature.
Why do beta thalassaemias present symptoms after birth?
Before birth, foetal haemoglobin in beta chains, hence faulty gene not yet expressed.
Alpha chains cant form stable tetramers!
Difference between fructosuria and fructose intolerance
Fructosuria simply means fructose in the urine, which is due to an absence of fructokinase
Fructose intolerance is far more serious, it is an absence of aldolase - which converts fr-1-p to GP
This leads to liver damage
Main polysaccharide in mammals and where?
Glycogen
Liver and skeletal muscle (more sm hence more there)
Alpha 1-4; 1-6(branches) glycosidic bonds
Main polymer of glucose in plants
Starch
Mixture of amylose and amylopectin
GI enzymes release glucose and maltose
Cellulose facts. Go.
Glucose polymer
Plants
Beta 1-4 linkages hence undigestable by humans
Enzymes involved in breakdown of dietary carbs
Saliva - Amylase
Pancreas - Amylase
Small intestine - Disaccharidases attached to brush border of epith cells. Lactase, sucrase, pancreatic amylase(a1-4), isomaltase (a1-6)
Which GLUT controlled by insulin
Glut 4
Why is glucose a major requirement in blood?
All tissues can metabolise glucose, and some NEED it
Rbc, wbc, kidney medulla, lens of eye
Cns prefers glucose
Pentose phosphate pathway function
Produce NADPH in cytoplasm (lipid synth, maintains free sulphydryl groups - cysteine)
Produce C5 sugars
Not enough O2, how regenerate NAD+
Lactate dehydrogenase
Produced by RBC, skeletal muscle
Released into blood
Normally metabolised by liver & heart
Lactate can be utilised by liver, via gluconeogenesis. Give examples of when this may not happen.
Impaired in liver disease
Vitamin deficiency - thiamine
Alcohol NAD+ -> NADH
Enzyme deficiencies
Glucose-6-phosphate dehydrogenase deficiency
Cant produce NADPH via Pentose Phosphate Pathway, hence heinz bodies in RBC; cataracts in eyes (free S-S not maintained)
Is Pentose phosphate pathway reversible
No
CO2 released
What is the link reaction
Pyruvate to Acetyl CoA
Using pyruvate dehydrogenase
How can a Vitamin B1 (thiamine) deficiency potentially cause serious issues (think about Pyruvate)
Pyruvate dehydrogenase is multi complex enzyme
Vit B1 = cofactor
Result of PDH deficiency (pyruvate dehydrogenase)
Lactic acidosis
How to stop final stage of catabolism?
Final stage is electron transport coupled to ATP synthesis
CN- stops electron acceptance by O2
Uncouplers increase permeability of mitochondrial inner membrane - dissipating proton gradient - e.g. Dinitrophenol, thermogenin
How do fluffy cute little hibernating animals stay warm?
They have brown adipose tissue, which contains thermogenin.
In response to cold, noradrenaline activates lipase -> fatty acids released, get oxidised, and activate thermogenin
Thermogenin transports H+ back in to mitochondria (dissipating the proton motive force), energy is released as heat (instead of ATP via ATP sythase)
Why does an oxygen binding curve for haemoglobin look sigmoidal vs myoglobin, which is hyperbolic?
Myoglobin binding simply dependent on oxygen concentration
Whereas deoxyhaemoglobin has two states - low affinity T, high affinity R.
O2 binding promotes stabilisation of R state. Co-operative binding - i.e. Binding affinity for oxygen increases as more o2 molecules bind to Hb subunits
What is 2,3-BPG and why is it important?
It is a regulator of O2 affinity (decreases), with one in every Hb tetramer in RBC.
formed from glycolysis intermediate, 1,3-BPG, via enzyme bisphosphoglycerate mutase
Bohr effect
Binding of H+ and CO2 lowers affinity of Hb for oxygen
Hence metabolically active tissues get O2 required
Why is CO poisonous?
Binds to Hb 250x more readily than O2
Fatal when COHb >50%
Weirdly, it increases affinity for oxygen of unaffected subunits
But basically, not enough free Hb to carry required amount of O2
What is special about foetal haemoglobin?
HbF has higher binding affinity for O2 vs HbA hence allows transfer of O2 from mother
Binding of subtrates can induce changes in conformation of enzyme
What hypothesis am I talking about?
Induced Fit
What is the Michaelis-Menten model for enzyme catalysis?
A model that proposes that a specific complex between enzyme and substrate is a necessary intermediate in catalysis
Basically, Vo versus [S] will be a rectangular hyperbola
In Mic-menten kinetics, what is Vmax?
The maximal rate of reaction when all enzyme active sites are saturated with substrate
In mic-menton kinetics, what is Km?
The subtrate concentration that gives half maximal velocity of reaction
Km values give a measure of affinity of an enzyme for its subtrate. What affinity if low Km?
High affinity
Km values give a measure of affinity of an enzyme for its subtrate. What affinity if high Km?
Low affinity
Hexokinase - tissues
Glucokinase - liver
What is the difference?
Hexokinase has a lower Km, hence is always active
Glucokinase has higher Km, hence only becomes active when glucose levels peak after feeding
Activity of an enzyme is measured in…
Amount of enzyme that converts 1MICROmol of product per min under standard conditions
You have a lineweaver burk plot. Which intercepts indicate which values in terms of enzyme kinetics?
X intercept= 1/Km
Y intercept = 1/Vmax
How do competitive and non-competitive inhibitors differ in the way they affect Km and Vmax?
Comp affects Km not Vmax
Non comp vice versa
What is a nucleosome
DNA wrapped around octamer of histones- 2 of each:
H2a/b, h3,h4
H1 then is the ‘clip’ that stabilises
Heterochromatin vs euchromatin
Heterochromatin genes not expressed
Eu genes expressed
What is a genome?
Entire DNA sequence
Difference between nucleoside and nucleotide?
Base and sugar is nucleoside
Base, sugar and phosphate is nucleotide
Types of nitrogenous bases found in DNA (and RNA)
Adenine, guanine - purines
Cytosine, thymine - pyrimidines (uracil in RNA)
How is a phosphate attached to the ribose sugar in a nucleotide?
Phosphate ester link on carbon 5
Nucleotides are joined via …
Phosphodiester bonds, 5’-3’ polarity
Base pairs DNA (RNA)
Adenine // Thymine (Uracil)
Guanine /// Cytosine
Where can we see RNA stem loops?
Hydrogen bonds formed between anti-parallel complementary sequences,
Found in tRNA
What reaction is catalysed by DNA polymerase?
(dNMP)n + dNTP -> (dNMP) n+1 + PPi
Reaction driven by pyrophosphate hydrolysis
Three steps DNA replication prokaryotes
1) initiation
2) elongation
3) termination
What are okazaki fragments and why do they occur in DNA replication?
Because DNA polymerise works 5’-3’, hence primase needed so it can work - but in fragments
But DNA ligase needed to connect backbone
What is it about meiosis that generates genetic diversity?
- Random assortment of chromosomes
2. Crossing over of genetic material
Difference in meiosis of gametes male and female?
Male one spermatogonium = 4 mature sperm
Female one oocyte = 1 egg + 3 polar bodies
Example of autosomal recessive disease?
Cystic fibrosis
Example of autosomal dominant disease?
Huntingtons
Example of x-linked recessive disease?
Haemophilia A
Co-dominance genetic example
Blood groups
Linkage and recombination
Look it up
Give an example of a promoter sequence in prokaryotes and eukaryotes
Tata box prok
Prinbow box in euk?
Rna processing?
Capping (5’ cap protects against degradation)
Tailing/Polyadenylation (at 3’ end, “)
Splicing in the middle removes introns, sequence dependent
What do I need to make a polypeptide?
Ribosome, amino acids (substrate), mRNA (template),
Initiation elongation termination
What types of ribosomes euk prok
Euk 80s
Prok 70s
Initiation codon
AUG
Codes for methionine
What is a wobble position when it comes to tRNA?
5’ end of anticodon
3’ end of codon
Basically, there is a degree of flexibility here
One mrna could read multiple codons
How are tRNA molecules activated?
tRNA synthetase
Briefly describe translation in prokaryotes.
Initiation using AUG codon, methionyl tRNA brought to ribosome P site.
Next codon read, appropriate amino acyl tRNA brought to A site.
Peptidyl transferase forms peptide bond between both amino acids, leaving P site free.
Translocation of polypetide to P site, cycle repeats.
To terminate, stop codon allows water to be brought.
In which direction does protein synthesis occur?
N -> C
What is the mechanism behind pyruvate dehydrogenase deficiency?
Mutation that results in Arg to Pro substitution,
Hence ruins signal?
Less uptake in to mitochondria
Lactic acidosis, neurological problems
PCR
Uodhaefeajfjfo
Types of single base mutations
Missense - one amino acid substituted for another
Silent - no substitute of amino acid
Nonsense - STOP instead of amino acid (little or no protein may be made due to nonsense mediated decay - protective mechanism)
Frameshift - reading frame of mRNA altered (“)
Failure of DNA repair mechanisms can result in cancer. What genes are commonly mutated in cases of hereditary non-polyposis colorectal cancer?
MSH2 in 60% of families
Formation of a tumour needs 6 things. List them.
1) divide independently of external growth signals
2) ignore external antigrowth signals
3) avoid apoptosis
4) divide indefinitely without senescence
5) stimulate sustained angiogenesis
6) invade tissues and establish secondary tumours
What is epigenetic modification?
Genes only expressed from active chromatin
DNA demethylation, histone acetylation etc. can switch heterochromatin to euchromatin, without changing the actual DNA sequence itself. This is epigenetics.
Chromosome morphology key words. Go.
P arm is petit, q is long
Causes of aneuploidy
Non disjunction at one of the meiotic divisions
Forms gametes with missing and extra chromosomes
If occurs due to mitotic cell division, causes mosaicism
Or anaphase lag, chromosomes left behind in cell
Why is uniparental disomy a problem?
Imprinting, maternal and paternal chromosomes behave differently
Beta oxidation of fatty acids is NOT found in which tissues?
Brain
Rbc
Wbc
Briefly outline beta oxidation of fatty acids.
Mitochondrial
First activation, then carnitine to mitochondria
Cycle of reactions
Removal of 2c units per cycle
Stops in absence of O2
H+ and e- transferred to NAD+ and FAD, no ATP synthesis
TAG broken down in to Glycerol and Fatty acids. Fatty acids have undergone beta oxidation, what happens to glycerol?
Liver
Glycerol kinase-> glycerol phosphate
Can either be converted to DHAP and back into glycolysis
Or
TAG synthesis
Glycogenesis and glycogenolysis describe
Glucose hexokinase glucose 6 phosphate
Phosphoglucomutase - glucose1phosphate
Glycogen synthase or branching enzyme
To break down, glycogen phosphorylase and debranching enzyme (dif enzyme hence dif regulation). At end, G-6-P phosphatase in liver converts back to glucose
Difference in function of glycogen stores in liver and skeletal muscle?
G6P converted to glucose in liver using enzyme G6Phosphatase.
Enzyme not present in skeletal muscle, hence straight to glycolysis
Three major precursors of gluconeogenesis
Lactate (cori cycle)
Glycerol
Amino acids
Why can’t Acetyl~CoA be converted to glucose?
Because pyruvate dehydrogenase reaction is irreversible
Key enzymes in gluconeogenesis?
1) PEPCK
2) Fructose 1,6 bisphosphatase
3) Glucose-6-Phosphatase
Glucogenic and ketogenic amino acids
Both?
Glucogenic glycine
Ketogenic Lysine
Both Phenylalanine
What is the cause of refeeding syndrome?
Urea cycle enzyme levels matched with demand to dispose of ammonia - i.e. High protein diet.
Low protein diet / starvation represses levels,
cycle is inducible however, hence refeed gradually. Build up in a week.
Why is ammonia toxic?
Interferes with amino acid transport and protein synthesis
pH effects
Alteration of blood brain barrier
Inteferes TCA cycle
Phenylketonuria
Deficiency in phenylalanine hydroxylase (convrts phen to tyrosine)
Aut recess. Chromosome 12
Accumulation of phenylalanine in tissues, plasma and urine
Phenylketones in urine
Affects norad, ad, dopa, mel, thyroid, prot synth.
Symptoms: severe intellectual disability, developmental delay, microcephaly, seizures, hypopigmentation
Homocystinurias
Normally, methionine conv to homocysteine to cystathionine and finally cysteine (enzyme: CYSTATHIONINE BETASYNTHASE)
Problem breaking down methionine because no enzyme Excess homocystine (oxidised form of homocysteine) in urine
Why is cholesterol important?
Essential membranes
Steoid hormone precursor
Bile acid precursor
A 3 year old girl is admitted with fever, tachypnoea (rapid breathing), photophobia, neck stiffness and a non-blanching rash. Meningitis is suspected. A lumbar puncture is performed.
Q1. Suggest a suitable vertebral level at which the needle should be inserted. Explain the rationale for your choice.
Q2. State the structures through which the needle will pass through, in order from the skin to the subarachnoid space.
L2/3), L3/4 or L4/5 (after the conus medullaris so only mobile spinal nerve roots not cord; least chance of neurological damage)
• (Skin), subcutaneous tissue,
supraspinous ligament, interspinous
ligament, ligamentum flavum, epidural fat and veins, dura mater,
arachnoid mater, (subarachnoid space)
Atheroma
Accumulation of intra/extra cellular lipid in the intima and media of large and medium sized arteries
Define atherosclerosis vs arteriosclerosis
Thickening and hardening of arterial walls as a consequence of atheroma
Whereas arteriosclerosis is the thickening of walls of arteries and arterioles usually as a result of hypertension or diabetes mellitus
Common sites for atheroma
Aorta especially abdominal
Coronary arteries
Carotid arteries
Cerebral arteries
Leg arteries
Normal arterial structure
Endothelium
Sub endothelial c.t.
Internal elastic lamina
Muscular media
External elastic lamina
Adventitia
Microscopic features of atheroma
Early changes:
Proliferation of smooth muscle cells
Accumulation of foam cells
Extra cellular lipid
Later: Fibrosis Necrosis Cholesterol clefts \+/- inflammatory cells \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
Eventually Disruption of internal elastic lamina Damage extends into media Ingrowth of blood vessels Plaque fissuring
Virchow’s triad?
Endothelial injury
InflammationsjsjxgsizmxakcnznKzn Bc
Increased permeability to lipid from plasma
Briefly explain how atheromas are formed?
Endothelial injury due to
Raised LDL/toxins/hypertension/haemodynamic stress
Causes
Platelet adhesion, SMC proliferation and migration/insudation of lipid/LDL oxidation/migration of monocytes into intima
Stimulated SMC produce matrix material
Macrophages engulf lipids and become foam cells - they then secrete cytokines causing further SMC stimulation and recruitment of other inflammatory cells
Why doesn’t newly synthesised fatty acid immediately get transported to mitochondria and oxidised?
Because malonyl CoA inhibits the carnitine shuttle
What are the different classes of hormones and give an example of each.
Peptide hormones - insulin, glucagon, growth hormones
Amino acid derivatives - adrenaline, noradrenaline, thyroid hormones
Glycoproteins - LH, FSH, TSH
Steroids - cortisol, aldosterone, testosterone
Steroid hormones are synthesised from cholesterol
- Aldosterone
- Testosterone
- Progesterone
- Cortisol
How is the hypothalamus connected to the pituitary
Directed connected to the posterior pituitary gland since hypothalamus drops down through the infundibulum to form posterior pituitary
Basic outline of regulation of blood calcium levels.
When Ca2+ low, PTH from PTG chief cells: Stimulates bone resorption, increases kidney reabsoprtion, decreases kidney reabsorption of phosphate. Also indirectly affects absorption via Vit D activation through kidneys.
Vit D -> calcitriol: increases ca absorption in gut, more bone resor., less urinary loss.
If high: Calcitriol - by parafollicular cells of THYROID! Not so relevant in humans.
What does hypercalcaemia lead to?
Stones moans (depression) and groans (abdo pain) Ttmt: fluids and surgery to remove parathyroid tumour
Glut transporters?
GLUT1 - RBC, BBB: low level basal glucose uptake for resp
GLUT2 - Two way, liver and b-cells of pancreas
GLUT3 - vv high affinity, brain
GLUT 4 - regulated by insulin. Skeletal muscle, adipose
acetaminophen(paracetamol) overdose, why is it dangerouus and what ttmt?
Normally paracetamol combined with sulphate. Okay.
High doses -> becomes NAPQI (toxic!), which uses up glutathione.
Acetylcysteine replenishes liver glutathione levels
Patent ductus arteriosus
Ductus arteriosus is present in foetus to shunt blood from pulmonary artery to aorta. Should close after birth, but if open blood flow will be from high to low pressure.
Mechanical murmur heard.
HOWEVER chronic shunting -> vascular remodelling, increase pulmonary resistance, MAY reverse!
Coarctation of the aorta
Narrowing of aortic lumen in region of ligamentum arteriosum. Narrowing increases afterload on left ventricle, left vent hypertrophy.
Upper limb branches prior to coarctation, hence lower limb femoral pulse weakened with upper hypertension
Tetralogy of fallot
1) VSD
2) Overriding aorta
3) pulmonary stenosis
4) right ventricular hypertrophy
Transposition of the great arteries
Not compatible with life after birth
Shunt must be created until surgery
What is stroke volume?
End Diastolic Volume - End Systolic Volume
Describe process of insulin synthesis and rlease from b cell of islet.
mRNA translated as one polypeptide: preproinsulin
Preproinsulin enters ER and has signal peptide cleaved, leaving proinsulin.
Proinsulin passes through golgi and is exposed to several specific endopeptidases, which excise the C-peptide- leaving insulin and C-peptide.
Insulin stays in cell until glucose comes in (GLUT2) and enters glycolysis, synthesis of ATP inhibits an ATP-sensitive potassium channel, reducing K+ efflux. This leads to depolarisation of the cell - and the v-gated Ca2+ channel opens. Ca2+ enters, inducing exocytosis of the insulin.
Difference between fecundity and fertility
Fecundity = physical ability to reproduce
Fertility = realisation of this potential as births
