Enzyme structure and function Knowledge-Based Download PDF

Questions

1. 1.

   In an experiment with a fixed enzyme concentration, the rate of product formation initially increases with substrate concentration but eventually reaches a plateau. Which of the following best explains this plateau in reaction rate?

   • A) Substrate molecules begin binding to allosteric sites, acting as noncompetitive inhibitors of the enzyme.
   • B) All available active sites are occupied by substrate molecules, so the reaction rate is limited by catalytic turnover.
   • C) The free energy change of the reaction shifts to zero, causing the net rate of the reaction to stop increasing.
   • D) High substrate concentrations cause enzyme molecules to denature due to excessive molecular collisions.
2. 2.

   Which of the following correctly explains how a noncompetitive inhibitor alters enzyme function?

   • A) It binds to an allosteric site separate from the active site, inducing a conformational change that reduces the enzyme's catalytic efficiency.
   • B) It binds directly to the active site in place of the substrate, preventing substrate molecules from entering the catalytic pocket.
   • C) It permanently denatures the enzyme by breaking the covalent peptide bonds forming its primary backbone structure.
   • D) It binds directly to free substrate molecules in solution, altering their chemical shape so they cannot fit the active site.
3. 3.

   Which of the following best describes the primary structural consequence when an enzyme is exposed to temperatures significantly above its optimal range?

   • A) Peptide bonds along the primary polypeptide backbone are hydrolyzed into free amino acids.
   • B) The enzyme reverses its net surface charge, converting it permanently into an inorganic catalyst.
   • C) Noncovalent interactions stabilizing the tertiary structure disrupt, altering the shape of the active site.
   • D) The active site covalently cross-links with surrounding solvent molecules, permanently locking the complex.
4. 4.

   Which of the following correctly describes how an enzyme alters the energetics of a biochemical reaction?

   • A) It increases the net change in free energy ($\Delta G$) between reactants and products.
   • B) It shifts the reaction equilibrium toward the formation of additional products.
   • C) It increases the kinetic energy of the reactants to surpass the activation barrier.
   • D) It lowers the activation energy of the reaction without changing the net free energy change ($\Delta G$).
5. 5.

   Which statement correctly describes how an enzyme interacts with its substrate to accelerate a chemical reaction?

   • A) An enzyme permanently alters its primary structure to provide energy directly to the reactants.
   • B) An enzyme increases the overall free energy change of the reaction by covalently consuming the substrate.
   • C) An enzyme prevents the formation of the transition state by stabilizing the detached products.
   • D) An enzyme binds the substrate at its active site and lowers the activation energy required to reach the transition state.