Factors affecting enzyme activity (temperature, pH, concentration) Knowledge-Based Download PDF

Questions

1. 1.

   Why does exposing an enzyme to temperatures well above its optimum result in an irreversible loss of catalytic activity, whereas exposure to near-freezing temperatures is typically reversible upon rewarming?

   • A) Freezing hydrolyzes the covalent peptide bonds of the enzyme, whereas excessive heat only neutralizes the surface charges of the substrate.
   • B) Excessive heat causes substrate molecules to degrade spontaneously, whereas freezing permanently alters the primary structure of the enzyme.
   • C) Freezing induces competitive inhibition by water molecules, whereas high temperatures convert the active site into an allosteric regulatory site.
   • D) Extreme heat disrupts the non-covalent bonds maintaining the tertiary structure of the active site, whereas low temperatures merely reduce molecular kinetic energy without denaturing the protein.
2. 2.

   Under conditions where substrate concentration is maintained in excess, what happens to the rate of an enzyme-catalyzed reaction as the enzyme concentration is steadily increased?

   • A) The reaction rate increases linearly because more active sites become available to catalyze the reaction.
   • B) The reaction rate remains constant because the catalytic efficiency of individual active sites decreases.
   • C) The reaction rate decreases progressively because enzyme molecules act as competitive inhibitors of one another.
   • D) The reaction rate plateaus rapidly because active sites become saturated with substrate molecules.
3. 3.

   Which of the following best describes the primary mechanism by which a significant deviation from an enzyme's optimal pH decreases its catalytic activity?

   • A) It alters the chemical composition of the substrate so that it becomes an unreactive optical isomer.
   • B) It alters the ionization state of amino acid side chains and disrupts ionic and hydrogen bonds maintaining the active site conformation.
   • C) It reduces the thermal kinetic energy of the molecules, preventing effective collisions with the substrate.
   • D) It irreversibly hydrolyzes the primary peptide backbone of the enzyme into individual free amino acids.
4. 4.

   Which of the following best explains why the rate of an enzyme-catalyzed reaction decreases sharply when the temperature drops well below the enzyme's optimum?

   • A) The kinetic energy of the molecules decreases, leading to fewer effective collisions between enzymes and substrates.
   • B) The covalent peptide bonds of the enzyme's primary structure hydrolyze into free amino acids.
   • C) The enzyme undergoes irreversible thermal denaturation that permanently alters its active site geometry.
   • D) Competitive inhibitors permanently bind to the active site due to the loss of thermal movement.
5. 5.

   In an enzyme-catalyzed reaction with a fixed enzyme concentration, increasing the substrate concentration eventually fails to further increase the reaction rate. Which statement best explains this plateau in reaction velocity?

   • A) Excess substrate acts as an inhibitor by altering the primary structure of the enzyme.
   • B) High substrate levels progressively increase the activation energy required for the reaction.
   • C) All active sites on the enzyme molecules are saturated with substrate, making enzyme concentration the limiting factor.
   • D) High substrate concentrations cause thermal denaturation of the enzyme's tertiary conformation.