Enzyme Catalysis Quiz

The lock and key model of enzyme catalysis suggests that enzymes are rigid structures with active sites that perfectly fit specific substrates.

• True

• False

Enzyme activity is unaffected by temperature.

• True

• False

Answer explanation

Enzyme activity is highly affected by temperature. Each enzyme has an optimum temperature at which it functions best. At low temperatures, enzyme activity is reduced due to insufficient kinetic energy. At high temperatures, enzymes can denature, losing their functional shape and activity.

Enzyme denaturation due to high temperature is a reversible process.

• True

• False

Answer explanation

Denaturation due to high temperatures is typically irreversible because it disrupts the enzyme's tertiary and quaternary structures, leading to a permanent loss of function. Some mild denaturation caused by non-extreme conditions may be reversible, but this is not common.

Allosteric enzymes can be regulated by both positive and negative effectors.

• True

• False

The rate of an enzyme-catalyzed reaction increases indefinitely with an increase in substrate concentration.

• True

• False

Answer explanation

The rate of an enzyme-catalyzed reaction increases with substrate concentration only up to a certain point, known as the saturation point. Beyond this, all enzyme active sites are occupied, and the reaction rate reaches a maximum (Vmax), beyond which additional substrate does not increase the rate.

Isoenzymes catalyze different reactions in the same tissue.

• True

• False

Answer explanation

Isoenzymes catalyze the same reaction but in different tissues or under different conditions. They differ slightly in structure but perform the same function, often tailored to specific cellular environments.

The optimum pH for most enzymes in the human body is between 7.0 and 7.4.

• True

• False

Allosteric inhibitors bind covalently to the active site of an enzyme.

• True

• False

Answer explanation

Allosteric inhibitors bind to a site other than the active site (the allosteric site) through non-covalent interactions. This binding induces conformational changes that affect enzyme activity. Covalent binding is characteristic of irreversible inhibitors, not allosteric ones.

Multienzymes are covalently bonded complexes of enzymes involved in sequential biochemical steps.

• True

• False

Answer explanation

Multienzyme complexes are usually non-covalently associated enzyme groups that catalyze sequential steps in a metabolic pathway. These associations allow for efficient substrate transfer between enzymes without covalent bonding.

Substrate saturation occurs when all enzyme active sites are occupied.

• True

• False