Enzyme Quiz
Questions: 16 · 10 minutes
1. Pepsin functions effectively in the acidic stomach but loses much of its activity at neutral pH. Why can this happen?
Neutral pH converts every pepsin molecule into a carbohydrate.
A pH change can alter charged groups involved in the active site's shape and binding.
Neutral pH removes all substrate molecules from the solution.
Neutral pH makes the reaction release more free energy than pepsin can absorb.
2. Enzymes A and B have the same maximum velocity, but A reaches half of that velocity at a lower substrate concentration. What does this suggest?
Enzyme A has a higher Km and lower apparent substrate affinity.
Enzyme B has a lower Km and higher maximum velocity.
Enzyme A has a lower Km and higher apparent substrate affinity.
Enzyme B must be permanently inhibited by its substrate.
3. What is a coenzyme?
The protein portion of an inactive conjugated enzyme
An inorganic ion that forms the enzyme's polypeptide chain
The reactant that is converted into product by an enzyme
A small organic helper molecule, often derived from a vitamin
4. What generally happens to an enzyme after it catalyzes a reaction?
It becomes part of the product and cannot be recovered.
It is converted into activation energy for the next reaction.
It changes the reaction's equilibrium constant before being degraded.
It emerges chemically unchanged overall and can catalyze another cycle.
5. In an experiment, substrate concentration is increased while enzyme concentration stays fixed. The reaction rate rises and then levels off. Why does it plateau?
The reaction's equilibrium constant increases at high substrate concentrations.
The added substrate has lowered the activation energy to zero.
Each enzyme molecule has been permanently consumed by one substrate.
Most enzyme active sites are occupied, so enzyme availability limits the rate.
6. A pure noncompetitive inhibitor binds equally well to free enzyme and the enzyme–substrate complex. What kinetic effect is expected?
Maximum velocity decreases while apparent Km remains unchanged.
Maximum velocity stays constant while apparent Km decreases.
Both maximum velocity and apparent Km increase.
Both maximum velocity and apparent Km remain unchanged.
7. The final product of a metabolic pathway binds to an enzyme near the start of that pathway and reduces its activity. What is this regulation called?
Feedback inhibition
Competitive activation
Substrate-level phosphorylation
Irreversible denaturation
8. Bread may taste slightly sweeter after prolonged chewing. Which process best explains this observation?
Salivary amylase begins breaking starch into smaller sugars.
Pepsin converts bread proteins directly into glucose.
Lipase converts starch into fatty acids in the mouth.
Lactase releases lactose from the bread's cellulose.
9. How do enzymes usually accelerate biological reactions?
They shift the reaction equilibrium toward the products.
They increase the overall free-energy change of the reaction.
They supply reactant molecules with permanent chemical energy.
They lower the activation energy required for the reaction.
10. A textual energy profile compares the same reaction with and without an enzyme. How should the enzyme-catalyzed pathway differ?
It should have a higher energy peak and a more negative overall free-energy change.
It should have a lower energy peak but the same overall free-energy change.
It should have lower-energy reactants and an unchanged energy peak.
It should have the same energy peak but produce higher-energy products.
11. Which statement best describes an enzyme's active site?
It is the region that permanently stores the reaction's products.
It is a separate molecule that transports the enzyme through a cell.
It is the region where specific substrates bind and catalysis occurs.
It is the sequence that signals the gene to produce the enzyme.
12. A person produces very little lactase. Which digestive process is most directly reduced?
The breakdown of starch in the mouth
The breakdown of protein in the stomach
The breakdown of lactose in the small intestine
The breakdown of triglycerides in the small intestine
13. A reversible reaction is already at equilibrium when an enzyme is added. What should happen?
The enzyme forces all remaining reactants to become products.
Only the forward reaction becomes faster, producing more product at equilibrium.
Forward and reverse reactions become faster, but the equilibrium position does not change.
The equilibrium constant decreases because activation energy is lower.
14. A human enzyme solution is heated to 80°C, cooled, and then mixed with fresh substrate. It remains almost inactive. What is the most likely explanation?
Cooling caused the substrate to become a competitive inhibitor.
High heat disrupted the enzyme's structure and altered its active site.
The reaction reached equilibrium before the fresh substrate was added.
The enzyme used up its activation energy while it was being heated.
15. Which description best represents the induced-fit model of enzyme action?
Substrate binding promotes a conformational change that supports catalysis.
The enzyme has a rigid active site that never changes during binding.
The substrate permanently reshapes itself before approaching the enzyme.
The enzyme and substrate merge into one permanent molecule.
16. A reversible inhibitor resembles the substrate and competes for the active site. Which change can often reduce its effect?
Lowering the substrate concentration
Increasing the substrate concentration
Removing all enzyme cofactors
Adding more reaction product