MChem Master of Chemistry Biochemistry and Chemical Biology

Question 1

What is the function of ATP synthase (Complex V) in oxidative phosphorylation?

Accepted Answer

It uses the proton gradient across the inner mitochondrial membrane to synthesize ATP from ADP + Pi

Answer

ATP synthase harnesses the proton motive force (proton gradient + membrane potential) built by the electron transport chain to drive the rotation of the F0 subunit and synthesize ATP.

Question 2

In enzyme kinetics, what does the Michaelis constant (Km) represent?

Accepted Answer

The substrate concentration at which reaction velocity is half of Vmax

Answer

Km is the substrate concentration at which reaction velocity equals Vmax/2, reflecting the apparent affinity of an enzyme for its substrate.

Question 3

Which type of enzyme inhibition increases the apparent Km without affecting Vmax?

Accepted Answer

Competitive inhibition

Answer

Competitive inhibitors bind the active site and increase apparent Km (reduced substrate affinity) but can be overcome by excess substrate, leaving Vmax unchanged.

Question 4

What is the role of coenzyme A (CoA) in metabolic pathways?

Accepted Answer

It activates and transfers acyl groups in fatty acid and carbohydrate metabolism

Answer

CoA forms high-energy thioester bonds with acyl groups (e.g., acetyl-CoA), activating them for transfer reactions in the citric acid cycle, fatty acid synthesis, and β-oxidation.

Question 5

What chemical modification is responsible for the activity of serine proteases like chymotrypsin?

Accepted Answer

A catalytic triad (Ser–His–Asp) that activates the serine hydroxyl as a nucleophile

Answer

The Ser-His-Asp catalytic triad lowers the pKa of serine, enabling it to act as a powerful nucleophile that attacks peptide carbonyl groups, forming an acyl-enzyme intermediate.

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Practice Test

MChem Master of Chemistry Biochemistry and Chemical Biology