MCQs

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.

An inactive apoenzyme becomes an active holoenzyme upon binding its required cofactor, a non-covalent, reversible process essential for regulation.

The active site, a 3D cleft formed by folding, provides the unique chemical and physical environment responsible for an enzyme's power and specificity.

Bell-shaped pH-activity profiles often reflect the ionization of catalytic residues that must be in a specific protonation state to function as acid/base catalysts.

In a coupled assay where enzyme Y and its substrates are in excess, the rate of product formation by Y is proportional to the rate at which X provides its substrate.

A non-competitive inhibitor binds to a separate site, forming a non-productive complex that lowers the concentration of functional enzyme, thus reducing Vmax.

A coenzyme acts as a co-substrate; it binds, accepts a chemical group from one substrate, and transfers it to another, being regenerated in the process.

Cofactors are non-protein components (metal ions or coenzymes) required for the activity of many enzymes, distinguishing simple from conjugated enzymes.

Group specificity means an enzyme acts on a family of structurally related substrates (like alcohols) due to shared functional groups.

A mutation in the small number of residues forming the active site would directly abolish enzyme function, unlike mutations in distant structural or surface regions.

The lock-and-key model proposes that the enzyme's active site (lock) is a rigid, pre-shaped template perfectly complementary to a specific substrate (key).

Once all substrate is consumed, adding more enzyme cannot generate more product, and the reaction rate plateaus due to substrate depletion.

Activation of zymogens requires specific, irreversible proteolytic cleavage to remove a blocking peptide, allowing the protein to fold into its active conformation.

Higher temperatures increase molecular kinetic energy, leading to more frequent and forceful collisions that increase the chance of overcoming the activation energy barrier.

Malonate is a structural analog of succinate and competes for the active site of succinate dehydrogenase, demonstrating competitive inhibition.