Free Biochemistry Enzymes and Metabolism Questions and Answers — Questions and Answers
Question 1: Which of the following statements about enzymes is TRUE?
- Enzymes are consumed during the reaction.
- Enzymes lower the activation energy of a reaction. (Correct answer)
- Enzyme activity is independent of temperature and pH.
- All enzymes require cofactors to function.
Correct answer: Enzymes lower the activation energy of a reaction.
Enzymes are biological catalysts that accelerate biochemical reactions by lowering their activation energy. They achieve this by binding to specific substrates at their active site, stabilizing the transition state, and facilitating product formation. Enzymes are not consumed during the reaction and can be reused multiple times.
Question 2: In glycolysis, which enzyme catalyzes the conversion of glucose to glucose-6-phosphate?
- Hexokinase (Correct answer)
- Phosphofructokinase
- Pyruvate kinase
- Aldolase
Correct answer: Hexokinase
Hexokinase is the enzyme that catalyzes the first committed step of glycolysis, converting glucose into glucose-6-phosphate. This phosphorylation traps glucose inside the cell, preventing its diffusion out and initiating its breakdown for energy. This reaction is crucial for cellular glucose metabolism.
Question 3: Which of the following is a key regulatory enzyme in the citric acid cycle?
- Citrate synthase
- Succinate dehydrogenase
- Isocitrate dehydrogenase (Correct answer)
- Malate dehydrogenase
Correct answer: Isocitrate dehydrogenase
Isocitrate dehydrogenase is a key regulatory enzyme in the citric acid cycle, controlling its overall rate based on the cell's energy demands. Its activity is allosterically inhibited by high levels of ATP and NADH, signaling ample energy, and activated by ADP, indicating a need for more energy. This regulation ensures efficient energy production.
Question 4: During oxidative phosphorylation, the final electron acceptor in the electron transport chain is:
- NAD⁺
- FAD
- Oxygen (O₂) (Correct answer)
- Water (H₂O)
Correct answer: Oxygen (O₂)
During oxidative phosphorylation, the electron transport chain passes electrons through a series of protein complexes, ultimately delivering them to oxygen. Oxygen acts as the final electron acceptor, combining with electrons and protons to form water. This crucial step drives the entire electron transport process and enables ATP synthesis.
Question 5: Which of the following statements about competitive inhibition is TRUE?
- Competitive inhibitors bind to the active site of the enzyme. (Correct answer)
- Competitive inhibitors reduce the Vmax of an enzyme.
- Competitive inhibition cannot be overcome by increasing substrate concentration.
- Competitive inhibitors form covalent bonds with the enzyme.
Correct answer: Competitive inhibitors bind to the active site of the enzyme.
Competitive inhibitors function by binding directly to the active site of an enzyme, competing with the natural substrate for access. Because they occupy the active site, they prevent the substrate from binding and undergoing catalysis. This type of inhibition can often be overcome by increasing the substrate concentration.
Free Biochemistry Enzymes and Metabolism Questions and Answers
Which of the following statements about enzymes is TRUE?