An active-site group donates a proton during bond cleavage. Which catalytic strategy is this?

• Covalent catalysis through a temporary enzyme-substrate bond
• Acid-base catalysis through proton transfer
• Proximity catalysis through positioning two reacting groups

A reaction is slow at body temperature because it has a high activation barrier. How can an enzyme help?

• By raising the temperature throughout the cell
• By providing a path with a lower barrier
• By changing the equilibrium constant toward products

An enzyme may form a temporary covalent bond during catalysis and still be regenerated after the cycle.

A change stabilises the transition state but leaves the bound-substrate energy unchanged. What happens to the barrier?

• It increases because the starting state has become lower
• It stays fixed because transition-state binding affects only equilibrium
• It decreases because the transition state is lower

A change stabilises the bound substrate but leaves the transition-state energy unchanged. What happens to the barrier from the bound state?

• It increases because the starting state is lower
• It decreases because the transition state is lower
• It stays fixed because binding never affects energy barriers

Why does an enzyme leave the equilibrium constant unchanged at a fixed temperature?

• It leaves the reactant-product free-energy difference unchanged
• It prevents products from reacting in the reverse direction
• It changes product concentrations until every substrate molecule disappears

Using one common energy scale, site A has bound-substrate energy -10 and transition-state energy 20. Site B has levels -25 and 20. Which has the lower barrier from its bound state?

• Site B: its barrier is 45, below site A's barrier of 30
• Both sites: their barriers are equal because their transition states match
• Site A: its barrier is 30, below site B's barrier of 45

Substrate binding changes an enzyme's shape and positions its catalytic groups. Which model describes this?

• Rigid lock-and-key binding without any shape change
• Induced fit during substrate binding
• Competitive inhibition by a molecule that replaces the substrate