MCQs

When substrate is in excess, the reaction rate is directly proportional to enzyme concentration because every additional enzyme molecule can contribute to the product formation rate.

The discovery of ribozymes (RNA catalysts) disproved the long-held belief that all enzymes are proteins.

Compartmentalization separates catabolic and anabolic pathways to prevent futile cycles and concentrates reactants to increase reaction efficiency.

A competitive inhibitor competes for the active site, requiring higher substrate concentrations to reach Vmax, thus increasing apparent Km.

High temperatures disrupt non-covalent bonds (e.g., hydrogen bonds) stabilizing protein structure, causing irreversible unfolding (denaturation) and loss of active site shape.

Irreversible inhibitors covalently modify essential residues or cofactors, leading to permanent enzyme inactivation.

The triad allows histidine to act as a powerful general base catalyst, abstracting a proton from the serine hydroxyl group to make it a nucleophile.

Non-allosteric enzymes follow Michaelis-Menten kinetics, where the plot of V₀ vs. [S] is a rectangular hyperbola: first-order at low [S] and zero-order at high [S].

An enzyme accelerates both forward and reverse reactions equally by lowering activation energy without changing the equilibrium point or free energy.

Carbonic anhydrase is so efficient that the rate-limiting step is the diffusion of the substrate into the active site.

Ligases catalyze the joining of two molecules with the concomitant hydrolysis of a high-energy phosphate bond, such as ATP.