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Phase 1 Notes > IMMS - Biochemistry > Flashcards

IMMS - Biochemistry Flashcards

1
Q

Describe the different molecules present on membrane

A

Phospholipid
Cholesterol
Intrinsic / Extrinsic proteins
Carbohydrates
Glycoproteins
Glycolipids

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2
Q

Describe aspects of channel proteins

A

Passive (leaky)
May be gated
Selective (size/ charge )
Usually ions or water
Integral

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3
Q

Describe aspects of carrier proteins

A

Specific binding site undergoes conformational change. Different types:
- Uniport = single substance
- Symport = two substances in the same direction
- Antiport - two substances in opposite directions
Can be active or passive

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4
Q

3 Driving forces of substances in/out of cells

A

-Chemical
-Electrical
-Electrochemical (both)

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5
Q

Describe the driving force - chemical

A

Forces directly proportional to the concentration gradient

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6
Q

Describe the driving force - electrical

A

(Also known as membrane potential)
Force depends on size of membrane potential and charge of ion

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7
Q

Describe the driving force - electrochemical

A

Net direction is equal to the sum of chemical and electrical forces
(Only charged substances e.g. K+)

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8
Q

Types of membrane transport

A

Passive
-Simple diffusion
-Facilitated diffusion (mediated by proteins) e.g. GLUT4 uptakes glucose regulated by insulin
Active
-Primary (directly uses source of energy ATP) e.g. 3Na+/2K+ATPase
-Secondary (uses energy from transport of an ion e.g. Na+/glucose)

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9
Q

What happens when GLUT4 carrier (in pregnancy) goes wrong?

A

GLUT4 carriers in skeletal muscle and adipose tissue.
Glucose is principal foetal nutrient and levels are directly related to mothers. (Foetal gluconeogenic enzymes are inactivated)
However no mechanism to limit uptake so excess glucose can cause foetal harm.

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10
Q

What happens when GLUT1 carriers (in the brain) goes wrong?

A

GLUT1 deficiency disorder caused by mutation in gene that encodes for less functional GLUT1. This reduces amount of glucose available for brain and can cause seizures etc.

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11
Q

What happens when there is a mutation in the ATP7B gene?

A

Wilson’s disease:
Cu2+ATPase in the liver transports copper into the bile and disorder results in deposition of copper in liver and other tissues (Rings in the eyes)

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12
Q

What is the function of SGLT1 carriers?

A

Transports glucose and galactose from the intestinal lumen.
If mutation reduces functionality, malabsorption may lead to chronic diarrhoea, dehydration etc.

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13
Q

Describe communication between cells (cellular signalling)

A

Signalling molecules bind to receptors:
-Intracellular e.g. steroid hormones
-Cell surface e.g. peptide hormones
Secondary messengers e.g. cAMP, Ca2+
= Affects gene expression in the nucleus

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14
Q

Give 4 types of cellular signalling receptors

A
  • Ligand gated ion channels
  • G protein coupled receptors
  • Enzyme linked receptors
  • Intracellular receptors
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15
Q

What happens when Gprotein coupled receptors goes wrong?

A

Cholera bacteria produce toxins that modify Gas subunits permanently and results in increased secondary cAMP levels. This results in massive secretion of ions and water into the gut = fatal dehydration and diarrhoea.

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16
Q

Give some examples of endocytosis and exocytosis

A

Endo:
Phagocytosis
Pinocytosis (smaller molecules)
Receptor mediated (more accessible)
Exo:
Insulin receptor
Synaptic cleft (triggered)

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17
Q

Describe cystic fibrosis

A

Mutation in CFTR protein (chloride channel) leads to abnormal sticky, viscous mucus and disallows osmotic drag

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18
Q

Give examples of drugs that target membrane transporters

A

Cardiac glycosides e.g. digoxin (Increases Ca2+)
Proton pump inhibitors e.g. omeprazole (Inhibits parietal cels)
Loop dietetics e.g. furosemide (On loop of Henle)
Thiazide dieuretics e.g. bendroflumethiazide (On distal tube to keep water in)

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19
Q

2 Functions of cell membrane

A

Cell polarisation/ compartmentalisation
Ionic gradient (membrane potential activates functions)

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20
Q

Describe K+ homeostasis failure in kidneys

A

High K+ conc = hyperkalaemia
(Em more positive so depolarises easier = bradycardia)
Low K+ conc = Hypokalaemia
(Em more negative = arrhythmia)

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21
Q

Definition of diffusion potential

A

Electrical force requires to cross a membrane to counterbalance chemical diffusion forces of a given ion.

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22
Q

Describe ischaemia

A

Hypoxia: ATP conc decreases so opens K+ channels and resting Em ~55mv. Depolarises easily
Slow Ca2+: early Repolarisation so shorter action potential

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23
Q

Name 5 different receptors

A
  1. Ion channels (target of most drugs)
  2. Membrane bound steroid receptors
  3. Neurotransmitters
  4. Growth factors
  5. Nuclear steroid receptors
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24
Q

Describe what 4 factors affect membranes

A
  1. pH = denatures
  2. Temperature = speed of activity
  3. Regulation of SAN action potential = ions lead to Brady/tachycardia
  4. Extra cellular ion concentration:
    - Acidosis = Less Ca2+ bound to plasma proteins
    - Alkalosis = more Ca2+ bound to plasma proteins
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25
Describe GPCRs
3 G-proteins (a,B,y) that are attached to enzymes which modulate secondary messengers (cAMP) and terminate signals.
26
Define homeostasis
Maintenance of a constant internal environment
27
Describe the 2 different communication systems
1. Endocrine - Hormones 2. Nervous - Electrical
28
Describe the 3 different categories of communication
Autocrine - cells to themselves Paracrine - To neighbouring cells (diffuses across gaps locally e.g. PDGF released by platelets) Endocrine - Hormones travel in blood (Organ = Thyroid, pituitary, ovaries, pancreas etc)
29
What is a hormone?
Molecule that acts as a chemical messenger
30
Describe the 3 different types of hormones
Amino acid derivative - synthesised from tyrosine e.g. adrenaline Peptide- made from amino acids, glycoproteins and is hydrophilic Steroids- made from cholesterol and is hydrophobic
31
Which hormones produce a quick reaction?
Peptide and amino acid derivatives - Are small and are pre made then stored in cell - Dissolves in blood and binds to receptor on target cell
32
Which hormones produce a slow reaction?
Steroid hormones (years) - Diffuses out once made and transported in blood via bound protein - Receptor is inside target cell and directly affects DNA
33
Difference between positive and negative feedback
Positive- signal is amplified Negative- Maintaining a steady state
34
What is freely permeable through the phospholipid membrane?
Gases Small uncharged polar Water
35
Describe structure of water
Polar as O is more electronegative Hydrogen bonding so universal solvent Maximum density at 4degrees so ice floats
36
Name some monosaccharides
Carbonyl, ketones, hydroxyl, aldehyde
37
How much ingested glucose does the brain use?
20% (If glucose less than 3 = hypogleicimic)
38
What are glycosidic bonds formed between?
2 monosaccharides = disaccharide 3-12 monosaccharides = ogliosaccharide More = polysaccharides e.g. starch, glycogen
39
Describe lipid structure
Straight carbon chains with carboxyl head group More unsaturated = m.p. Decreases Most stored and transported as triglycerides
40
Describe nucleotide structure
Nitrogenous base + sugar + phosphate
41
Describe amino acid structure
Amino, carboxyl and 20 different R groups R determines polarity In condensation reaction, loses water to form peptide bond
42
Describe protein structure
Primary - Peptide bonds between amino acids Secondary - H bonds fold chain into a-helix or B-pleated sheets Tertiary - H, ionic, disulphide, hydrophobic folds further Quaternary - More than 1 polypeptide
43
B-pleated sheets vs a-helix
B - H bonds between linear regions a - H bonds between carbonyl groups
44
Describe the 5 different bonds
Hydrogen - between dipoles of H + O/N/F Van dear Waal - weak electrostatic attraction due to fluctuations of electron density Ionic - Between fully or partially charged groups Disulphide + covalent bonds between S-S of cytosine Hydrophobic - Uncharged, non-polar side chains are hydrophobic
45
What are enzymes?
Biological catalysts that bind substances and alter bonds so there is a lower activation energy to form products. May also stabilise reaction intermediates to speed up reactions
46
Describe haemoglobin structure
Porphyria’s ring hold onto iron atom (heme) and is site of oxygen binding
47
3 factors influencing haemoglobin saturation
Temperature pH (H+ binds to Hb instead and O2 released) pCO2 (Modifies structure of haemoglobin to decrease O2 affinity and unload)
48
What is sickle cell anaemia?
Mutation in haemoglobin forms hard, sticky, sickle shaped red blood cells
49
What are immunoglobulins?
Antibodies produced to bind to antigens on microbial agents
50
DNA in prokaryotes vs eukaryotes
P - No nuclear membrane, DNA in single circular chromosome, super coiled E - DNA bound to proteins in nucleus. Chromatin condensed to chromosomes
51
Cell cycle is influenced by
Only starts if there is enough energy Oncogenes Proto-oncogenes Cell cycle repair DNA repair
52
Describe semi- conservative DNA replication
DNA helicase opens up DNA SSB proteins keep trands open and Topoisomerase unwinds it DNA Polymerase forms new DNA behind the fork
53
How are DNA damaged?
UV IR Ingesting benzene
54
Name some DNA repair mechanisms
Tumour suppress genes Apoptosis Pause cell cycle
55
Describe protein formation
Double stranded DNA transcripted Single stranded mRNA spliced to remove introns rRNA combines with proteins to from ribosomes tRNA carries amino acids in translation
56
What are transcription factors?
Control whether gene is turned off or only binding to specific exon and weakening helix
57
Factors that turn off expression
Methylation of cysteine Less acetylation of his tones Reverse transcriptase and retroviruses Activation of repressors
58
What do growth hormones do?
Bind to and activates kinase = phosphorylase’s a transcription factor = transcription occurs
59
Anabolic vs Catabolic
A - Synthesises larger molecules from smaller C - Breaks down large molecules to smaller
60
4 ways dietary components are metabolised
Bio synthetic (A) Fuel storage (A) Oxidative processes (C) Waste disposal
61
Where is energy stored?
Adipose tissue - 85% fat, energy rich molecules e.g. triglycerides Liver - glycogen, water Muscle - kinetic energy, glycogen, protein
62
3 main dietary fuels
Carbohydrates e.g. glucose, fructose … Lipids (1 glycerol esterified to 3 saturated fatty acids) Proteins
63
Energy per gram for 3 main dietary fuels
Carbohydrate - 4Kcal/g (sustains 12 hours) Protein - 4Kcal/g (when muscle glycogen stores fail) Alcohol - 7Kcal/g Lipid - 9Kcal/g (up to 12 weeks)
64
Define Basal Metabolic Rate (BMR)
Energy needed to stay alive at rest E.g. respiration, ion gradients, repairing, contraction of heart muscle, biosynthesis
65
Conditions to measure BMR
12 hour fast, 27-29degrees environment, no tea/coffee/nicotine for 12 hours, lying still. (If not met = RMR Resting Metabolic Rate)
66
Factors affecting BMR
Age Gender Dieting / starvation BMI Decreased muscle mass Hyperthyroidism Fever
67
Body Mass Index vs Basal Metabolic Rate
BMI (kg/m2) - released to height and weight BMR (kcal/kg/hour) - amount of calories for essential function
68
What is the recommended kcal/kg/day?
23-35
69
Define malnutrition
A state of deficient nutrient, energy or others causing measurable adverse affects
70
What is refeeding syndrome?
Too many carbs too quickly = lots of insulin = deficiency of enzymes
71
What happens in an overnight fast?
Glycogenolysis, insulin decreases
72
What happens in 2-4 day fast?
Insulin and cortisol decrease Lipolysis, preoteolysis, gluconeogenesis
73
What happens in more than 4 day starvation
Liver produces ketones from fatty acids Brain adapts to using ketones
74
Describe adenosine triphosphate (ATP) structure
Adenine (purine) base, ribose sugar, 3 phosphate
75
What does ATP form to release energy?
ADP + Pi Last 2 phosphate groups repel each other and is easily hydrolysed to release lots of energy
76
How are proteins, carbohydrates and fats metabolised?
Proteins -> amino acids Carbohydrates -> glucose -> glycolysis Glycerol -> fatty acids -> Acetyl coA -> Krebs cycle/citric acid/TCA cycle -> Oxidative Phosphorylation
77
Describe the preparation phase of glycolysis
Glucose enters cytosol via GLUT-1 transporters Glucose - (ATP->ADP) -> Glucose-6-phosphate Phosphorylation catalysed by hexokinase -> Fructose-6-phosphate (catalysed by phosphoglucoisomerase) - (ATP->ADP) -> Fructose-1,6-biphosphate (catalysed by phosphofructokinase) Splits into (catalysed by aldolase): Dihydroxyacetone phosphate (isomerise catalyses->) Glyceraldehyde-3-phosphate ———>
78
Describe the ATP generating phase of glycolysis
G-3-P is oxidised to 1,3-biphosphoglycerate (2NAD+ reduced to 2NADH +2H+ Catalysed by triose phosphate dehydrogenase) 1,3-BPG - (2ADP -> 2ATP) -> 3-phosphoglycerate (Catalysed by phosphoglycerokinase) Phosphoglyceromutase catalyses 3-PG to 2-PG Enolase catalyses to phosphoenolpyruvate (+2H2O) Pyruvate Kinase catalyses to pyruvate (2ADP->2ATP)
79
Why is glycolysis important?
Vital for emergency energy with limited O2: .RBC don’t have mitochondria .Muscle have fast energy demands .Glycerol-3-P is backbone for triglycerides .Pyruvate transaminated to alanine/substrate for fatty acid synthesis .G-6-P for glycogen synthesis/nucleotides
80
Summarise the glycolysis step
In cytosol, anaerobic breakdown of 1 glucose to 2 pyruvate, 2NADH and net 2 ATP
81
Describe regulation of glycolysis
Hormones (insulin + glucagon) indirectly increases/decreases gene expression through regulatory molecules. At 3 kinase reactions (hexokinase, pyruvate kinase, PFK-1) binds to non-catalytic site and conformational change increases/decreases substrate affinity
82
What is the primary regulatory site of glycolysis?
PFK-1
83
Activators and inhibitors of glycolysis
A - ADP is converted to AMP when accumulated which activates PFK1 to generate ATP I - ATP and citrate from Krebs cycle inhibits PFK1 I - Fructose-2,6-biphosphate inhibits PFK1
84
Describe link reaction (aerobic conditions)
Pyruvate enters mitochondria and is decarboxylate oxidated to Acetyl-CoA, NADH and CO2 by pyruvate dehydrogenase
85
Describe link reaction (anaerobic conditions)
Each pyruvate forms lactate, 2H2O and 2ATP catalysed by lactate dehydrogenase and energy regenerates NAD+ for glycolysis
86
An overview of the Krebs cycle
In matrix under aerobic conditions. Acetyl-CoA + 2H2O oxidative decarboxylated twice to form 2CO2, 3NADH, FADH, ATP
87
Describe the Krebs cycle
Acetyl-CoA combines with oxaloacetate to form citrate (citrate synthase) -> isocitrate (aconitase) -> a-ketoglutarate, CO2, NADH (isocitrate dehydrogenase) -> succinyl-CoA, CO2, NADH (a-ketogluterate dehydrogenase) -> succinct + ATP (succinyl-CoA thiokinase) -> fumarate + FADH (succinctly dehydrogenase) -> malate (fumarase) -> oxaloacetate + NADH (malate dehydrogenase)
88
Krebs cycle regulators
ATP activates pyruvate dehydrogenase (link) But inhibits first 3 Krebs enzymes Most activated by substrate and inhibited by product
89
Describe oxidative phosphorylation
NADH and FADH are oxidised to release H+ and e-. The e- pass down a series of electron carriers and energy released actively transports H+ into inter membrane space. H+ diffuses back into matrix through ATPsynthase which supplies energy for ATP formation. (O2 = terminal e- acceptor to form water) = Forms 34 ATP
90
What are the 3 steps of fatty acid breakdown?
Fatty acid activation Fatty acid B-oxidation Utilisation of Acetyl-CoA
91
Describe fatty acid activation
Fatty acids are activated in cytoplasm before diffusing into mitochondria (Fatty acids with more than 14 carbons are actively transported) Fatty acid + ATP -> ACYL Adenylate +CoA-SH -> ACYL-CoA (acyl-CoA synthetase) *NOT ACETYL
92
Describe fatty acid B-oxidation
Oxidation -> Hydrolysis -> Oxidation -> Thiolysis Each cycle produces 1 NADH, 1 FADH Every cycle chops off 2C to produce an Acetyl-CoA. Therefore 12C chain produces 6 Acetyl-CoA Fats = more energy rich than carbs
93
Describe utilisation of Acetyl-CoA
Either most utilised via citric acid (TCA) cycle to produce glucose under normal metabolic conditions Or produces ketones in liver when large amounts of Acetyl-CoA generated exceeds TCA cycle.
94
Describe ketogenesis
2 Acetyl-CoA thiolysed to Acetoacetyl-CoA -> HMG-CoA -> Acetoacetate Acetoacetate can spontaneously decarboxylate to acetone of enzymatically converted to B-hydroxybutyrate (Utilised by all tissue but hepatic)
95
Describe regulation of ketogenesis
Affected by free fatty acid release from adipose tissue, amount of glucagon or insulin High ATP demand = more likely to oxidise Acetyl-CoA via TCA Low conc of G-3-P in liver increases ketogenesis
96
Describe diabetic ketoacidosis
Insulin deficiency = Gluconeogenesis. + glycogenolysis = Inhibition of Glycogen synthesis Increased lipolysis -> Hyperglycaemia + Increased Acetoacetate + beta-hydroxybutyrate
97
Describe alcoholic ketoacidosis
Depleted protein and carbohydrate stores = Decreased insulin = Increased glucagon = Decreased gluconeogenesis = Increased lipolysis -> Increased ketone production
98
When does ketoacidosis occur?
In carbohydrate storages, heart + skeletal muscle utilise ketone bodies for energy, preserving glucose for the brain. Occurs in chronic alcohol abuse, type 1 diabetics and starvation.
99
Consequences of ketoacidosis
Ketones are strong acids and lower blood pH = Impairs ability of haemoglobin to bind to O2 Gets rid of CO2 = hyperventilating + fast respiration Low pH, High O2, Low CO2, Low HCO3-

Phase 1 Notes (9 decks)

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