Glycolysis

Question 1

1st committed step of glycolysis

Answer 1

Phosphofructose kinase (PFK)

Question 2

3 irreversible steps for 3 enzymes (sites of regulation)

Answer 2

Hexokinase,
Phosphofructokinase,
Pyruvate kinase

Question 3

3 parts of Glycolysis

Answer 3

1. Priming
   - Hexokinase or Glucokinase
   - Phosphoglucose isomerase,
   - Phosphofructokinase (PFK-1)
2. Cleavage (Aldolase)
3. Oxido-reduction-phosphorylation
   - Glyceraldehyde 3-P-d/h
   - Phosphoglycerate kinase
   - Pyruvate kinase

Question 4

Hexokinase vs Glucokinase

Answer 4

Hexokinase: most tissues EXCEPT LIVER
-Km(glucose): ~0.1mM
-product inhibition
-high affinity for glucose (allow for utilisation even when low blood glucose)
Glucokinase: Liver
-Km(glucose): ~10mM
Allosterically regulated 
(inhibitory ptn)
allosteric inhibitor: fructose-6-P
Allosteric activator: fructose-1-P
-Buffering effect on blood glucose

Question 5

Glycolysis reaction

Answer 5

C6H12O6 + 2 NAD+ + 2 ADP + 2 P —–> 2 pyruvic acid, (CH3(C=O)COOH + 2 ATP + 2 NADH + 2 H+

Question 6

Phosphofructokinase function & struc

Answer 6

Tetramer w 2 conformations: T&R

convert F6P –> FBP

Question 7

Molecules that alter PFK activity

Answer 7

ATP
-Both substrate & allosteric inhibitor
ADP, AMP, F2,6P
-Activators: reverse inhibitory effects of ATP

Question 8

T&R states regulation of PFK

Answer 8

2 ATP binding sites per subunit
Inhibitor (I) & Substrate (S)
At I: ATP binds well in T state
At S: ATP binds equally well in both R &T states
F6P binds F-site
At low ATP: I not occupied so F6P binds at F
At high ATP: I occupied by ATP so F6P cannot bind to F-site (shift balance to T state)

Question 9

Disorders of fructose metabolism

Answer 9

Essential fructosuria- deficiency of fructokinase in liver
Hereditary fructose intolerance- deficiency of F1P aldolase in liver, kidney cortex and small intes. Prolonged intake of fructose can lead to death
Hereditary fructose1,6Bphosphatase deficiency- results in severe impairment in gluconeogenesis. Fatal in infants.

Question 10

Disorders of galactose metabolism

Answer 10

A)Classical galactosemia- loss of uridyltransferase
B)Galactosemia- loss of galatokinase
-both are lactose intolerant, can lead to blindness and fatal liver damage due to high levels of galactose
C)Epimerase deficiency- 2forms, one benign, other similar to transferase deficiency

Question 11

Excess galactose accumulated is reduced to galactitol

Galactitol accumulation in eye leads to…

Answer 11

cataract