Question

MULTIPLE CHOICE

1. Many of the catabolic pathways converge to the common two-carbon intermediate:
a. alanine.
b. acetyl group of acetyl-CoA.
c. lactic acid.
d. glucose.
e. carbon dioxide.

2. The lower (“energy payoff”) part of glycolysis:

1. Only involves steps with DG close to zero, so it does not need to be regulated.
2. Involves the formation of metabolites with high-energy phosphates.
3. Involves enzymes that hydrolyse ATP to drive the pathway forward.
4. Oxidises NADP⁺ to NADPH.

3. Gluconeogenesis begins with the conversion of pyruvate to phosphoenolpyruvate (PEP), bypassing the reverse reaction which is catalysed by pyruvate kinase in glycolysis. Which of these statements about the conversion of pyruvate to phosphoenolpyruvate is FALSE?

1. It requires the input of energy from hydrolysing both ATP and GTP.
2. There is no allosteric regulation because pyruvate kinase is regulated.
3. 3-carbon pyruvate first needs to be converted to 4-carbon oxaloacetate.
4. It involves the enzymes pyruvate carboxylase and PEP carboxykinase

4. Triose phosphate isomerase was the first enzyme to be described as a “perfect catalyst”. Which of these statements about perfect catalysts is FALSE?

1. They have a catalytic efficiency (k_cat/K_M) greater than 10⁸ M^-1s^-1.
2. The rate-limiting step is either diffusion of the substrate into the active site, or diffusion of the product out.
3. The highest free energy barrier is associated with the transition state.
4. Perfect catalysts cannot evolve to be any more efficient.

Answer 1

Q.1.b. Acetyl group of acetyl- CoA.

Q2. Involves formation of metabolites with high energy phosphate.

1, 3-Bis Phosphoglycerate is the first 'high-energy' phosphate compound in glycolysis lead to reduction of NAD+ to NADH during payoff phase.

Q.3 b. There is no allosteric regulation because pyruvate kinase is regulated.

Pyruvate kinase is allosterically activated by fructose-1,6-bisphosphate & inhibited by ATO & alanin.

Q. 4. C. The highest free energy barrier is associated with the transition state.

Trios phosphate isomerase form low barrier hydrogen bond.