Enzyme structure and function Knowledge-Based Practice

Questions

1. 1.

   Which of the following statements correctly describes the effect of an enzyme on the thermodynamic equilibrium and net free energy change ($\Delta G$) of a chemical reaction?

   • A) An enzyme shifts the chemical equilibrium toward products by decreasing the net free energy change ($\Delta G$).
   • B) An enzyme leaves both the chemical equilibrium and the net free energy change ($\Delta G$) unaltered.
   • C) An enzyme converts an endergonic reaction into an exergonic reaction by lowering the net free energy change ($\Delta G$).
   • D) An enzyme increases the equilibrium constant ($K_{eq}$) by lowering the standard free energy level of the products.
2. 2.

   Which of the following statements correctly describes the physical state and availability of an enzyme immediately following the completion of a catalytic cycle and the release of products?

   • A) The enzyme is degraded into free amino acids to prevent reverse catalysis from taking place.
   • B) The enzyme permanently retains the distorted shape formed during the transition state, rendering it inactive.
   • C) The enzyme remains covalently bonded to the released products until transported across the plasma membrane.
   • D) The enzyme returns to its original active conformation without being consumed or permanently altered by the reaction.
3. 3.

   Which of the following best explains why an enzyme typically catalyzes only one specific chemical reaction?

   • A) All enzymes share an identical primary amino acid sequence that recognizes a universal chemical bond.
   • B) Enzymes break and reform their covalent peptide bonds during each catalytic cycle to adapt to any available reactant.
   • C) The active site consists of non-specific lipid regions that bind indiscriminately to polar functional groups.
   • D) The unique three-dimensional folding of the polypeptide forms an active site with precise chemical and spatial complementarity to the substrate.
4. 4.

   Which of the following statements best explains how an enzyme increases the rate of a chemical reaction?

   • A) By increasing the total change in free energy ($\Delta G$) between reactants and products
   • B) By supplying metabolic heat to raise the temperature of the active site microenvironment
   • C) By lowering the activation energy barrier required to reach the transition state
   • D) By shifting the chemical equilibrium of the reaction toward greater product yield
5. 5.

   Which statement correctly describes how an enzyme interacts with its substrate according to the induced-fit model?

   • A) The active site maintains a completely rigid conformation before, during, and after substrate binding.
   • B) The enzyme permanently changes its primary amino acid sequence upon contacting the substrate.
   • C) The binding of the substrate induces a subtle conformational change in the active site to optimize catalysis.
   • D) The substrate is converted into products entirely before making physical contact with the catalytic residues.

Answers and step-by-step solutions appear after you finish the test.