MCBG

Question 1

Essential amino acids

Answer 1

If Learned This Huge List May Prove Truly Valuable
Conditionally essential AA: cysteine, tyrosine, arginine
Isoleucine
Lysine
Tryptophan 
Histidine
Leucine
Methionine
Phenylalanine 
Threonine
Valine

Question 2

Essential vitamins and deficiencies

Answer 2

Fat soluble vitamins:
A: deficiency causes xeropthalmia
D: rickett’s/osteomalacia
E: neurological abnormalities 
K: defective blood clotting

Water soluble:
B12: anaemia
C: scurvy

Question 3

Lactose intolerance types

Answer 3

Primary lactase deficiency: absence of lactase persistence allele
Secondary lactase deficiency: caused by injury to small intestine (gastroenteritis, coeliac disease, Crohn’s disease, ulcerative colitis) is usually reversible
Congenital lactase deficiency: Very rare, autosomal recessive defect in lactase gene hence cannot digest breast milk

Question 4

Glucose transporters

Answer 4

Glut1: adult erythrocytes, fetal tissues, BBB
Glut2: small intestine, kidney, liver, pancreatic beta cells
Glut3:neurones, placenta
Glut4: adipose tissue, striated muscle (insulin regulated)
Glut5: intestine, spermatozoa

Question 5

Glycolysis enzymes

Answer 5

Hexokinase, phosphofructokinase-1* (key rate controlling enzyme), pyruvate kinase

Question 6

Glycerol phosphate role

Answer 6

Converted from glyceraldehyde-3-phosphate, required for triglyceride and phospholipid synthesis

Enzyme= glycerol 3-phosphate dehydrogenase

Question 7

2,3 bisphosphoglycerate role

Answer 7

Reversible reaction to form 1,3 bisphosphoglycerate
Produced in rbc, regulates O2 affinity (promotes release)
Enzyme= bisphosphoglycerate mutase

Question 8

Fructose metabolism issues

Answer 8

Essential fructosuria: lack fructokinase so fructose not digested and excreted
Fructose intolerance: aldolase B missing, Fructose-1-phosphate accumulates leading to liver damage, treatment=remove fructose from diet

Question 9

Galactosaemia symptoms + causes

Answer 9

Deficiency in galactokinase, uridyl transferase or UDP-galactose epimerase
Galactose accumulation leads to galactitol production via aldose reductase, more NADP+ produced, innapropriate disulphide bond formation, loss of integrity of some proteins e.g lens of eye (cataracts)

Question 10

Significance of pentose phosphate pathway

Answer 10

Glucose-6-phosphate exits glycolysis, forms ribose-5-phosphate required for DNA, RNA, coenzymes
Occurs in cytosol, can re-enter glycolysis
Forms NADPH (IMPORTANT AS G-6-P DH DEFICIENCY CAUSES OXIDATIVE STRESS, HEINZ BODIES, HAEMOLYTIC ANAEMIA) and CO2
Glucose-6-P -> 5c sugar+ CO2 (forms NADPH, catalysed by GLUCOSE-6-P DEHYDROGENASE)

Question 11

Glycolysis points of regulation

Answer 11

Metabolic regulation: ^[ATP] inhibits PFK, ^[NADH] inhibits step 6
Hormonal activation: ^ by high insulin:glucagon ratio
Hexokinase allosterically inhibited by glucose-6-phosphate

Question 12

Pyruvate dehydrogenase roles

Answer 12

(Essentially link reaction)
Multi-enzyme complex catalyses pyruvate+ coA-> acetyl coA
Irreversible reaction hence key regulatory step
PDH deficiency leads to lactic acidosis
Reaction is sensitive to vit B1 deficiency

Question 13

Fatty acid metabolism key points

Answer 13

TAG packaged in chylomicrons and absorbed through small intestine
FA activated (links to coA outside mitochondrion)
Moved through inner mitochondrial membrane via cartinine shuttle
Beta oxidation forms acetyl coA, acetyl coA enters krebs or…
Acetyl coA converts to HMG coA and then (Well fed state) converts to mevalonate, then cholesterol using HMG coA reductase
(Starved state) converts to actoacetate (+other ketones) via HMG coA lyase

Question 14

3 main ketones, use+production

Answer 14

Acetone
Acetoacetate
Beta hydroxybutyrate

Ketones produced in liver, spare glucose usage in starvation for glucose requiring cells, are either metabolised or converted into cholesterol
HMG coA lyase converts HMG coA into ketones, HMG coA reductase converts HMG coA into cholesterol

Question 15

Enzyme regulation mechanisms

Answer 15

Isoenzymes- different AA sequence but catalyse the same reaction
Allosteric regulation- T state= low affinity, R state= high affinity, binding away from active site leads to conformational change

Question 16

Regulation of clotting

Answer 16

1. Inactive zymogens present at low conc
2. Proteolytic activation leads to amplification by cascade
3. Clotting factors cluster, thrombin causes feedback activation- coverts fibrinogen to fibrin
4. Termination of clotting- multiple mechanisms, regulated by proteolytic activation

Question 17

Collagen synthesis

Answer 17

1. Cleavage of signal peptide
2. Hydroxylation of proline+ lysine molecules
3. Addition of N linked oligosaccharides and galactose in ER
4. Disulphide bond formation
5. Procollagen transported to Golgi
6. O-linked glycosylation in Golgi
7. Golgi- exocytosis as tropocollagen
8. Removal of N and C terminal propeptides
9. Lateral aggregation to form fibrils

Question 18

Where are the DNA checkpoints? What repair is undertaken?

Answer 18

Gap phase 1+ Gap phase 2+ mitosis

Base excision repair, mismatch repair, nucleotide excision repair, recombinational repair

Question 19

Centromere locations

Answer 19

P arm= short, Q arm= long

Metacentric= central
Submetacentric= close to central
Acrocentric= P arm is very short
Telocentric= centromere is at telomere

Question 20

Gamete production/ derivatives

Answer 20

Spermatogonium-> primary spermatocyte-> spermatids-> mature sperm

Oogonium-> primary oocyte-> polar bodies-> 1 mature ovum

Question 21

Genetic disease examples

Answer 21

Autosomal recessive- cystic fibrosis
Autosomal dominant- Huntington’s disease
X-linked recessive- haemophilia A (all males affected, inherited from mother)
X-linked dominant- fragile X syndrome
Y-linked- colour blindness (only males affected- linked to ‘maleness’)
Mitochondrial- mitochondrial myopathy (inherited from mother)

Question 22

Transcription+ translation

Answer 22

Transcription initiation- DNA sequence read 3’ to 5’, catalysed by RNA polymerase, transcription factors bind to promoter

Translation- capping (5’ cap), splicing (removal of introns, exons joined by spliceosomes), tailing (3’ polyA tail)

Question 23

What happens to Lineweaver-Burke plot with addition of inhibitors?

Answer 23

Linear graph

Addition of competitive inhibitor: gradient increases, x intercept moves right

Addition of non-competitive: x intercept doesn’t change, gradient increases

Question 24

Glucose dependant cells

Answer 24

Red blood cell (erythrocytes)
Neutrophils
Lens of eye
Innermost cell of kidney medulla

Question 25

Molecular techniques

Answer 25

FISH: fluorescent in situ hybridisation, used to detect aneuploidy etc, label w/ fluorescent dye then denature and hybridise
Southern blotting: DNA hybridisation+ gel electrophoresis, uses probes, investigate gene structure
Microarray: many genes analysed simultaneously, monitors change in gene expression
SDS PAGE: protein gel electrophoresis, separates proteins based on size
Agarose gel electrophoresis: separates DNA based on size/shape
PCR: analyses small changes in DNA sequence, primer annuals to sequence, taq polymerase replicates, heated + cooled to replicate