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

Questions

1. 1.

   In an enzyme-catalyzed reaction where substrate is present in excess, what is the effect of continuously increasing the enzyme concentration on the reaction rate?

   • A) The reaction rate remains constant because substrate availability limits any further catalytic activity.
   • B) The reaction rate decreases because redundant enzyme molecules competitively inhibit each other.
   • C) The reaction rate increases proportionally because additional active sites become available to bind substrate molecules.
   • D) The reaction rate initially increases but subsequently drops to zero due to crowding-induced denaturation.
2. 2.

   Which statement best explains why an enzyme-catalyzed reaction rate decreases significantly when the temperature is lowered well below the enzyme's optimum?

   • A) The covalent peptide bonds forming the enzyme's primary structure are cleaved.
   • B) The kinetic energy of molecules decreases, resulting in fewer effective collisions between enzymes and substrates.
   • C) The enzyme undergoes irreversible denaturation, permanently altering the shape of its active site.
   • D) The chemical charge of the substrate molecule is neutralized, preventing it from entering the active site.
3. 3.

   Which statement best explains why altering the pH away from an enzyme's optimum level decreases the rate of an enzyme-catalyzed reaction?

   • A) It degrades substrate molecules by hydrolyzing their internal covalent bonds prior to binding.
   • B) It breaks the covalent peptide bonds of the enzyme, completely hydrolyzing its primary structure into free amino acids.
   • C) It alters the charges of amino acid R-groups, disrupting ionic interactions and distorting active site geometry.
   • D) It lowers the thermal kinetic energy of the system, reducing effective collision frequencies between enzyme and substrate.
4. 4.

   Which statement correctly explains why an enzyme-catalyzed reaction rate sharply decreases when the temperature rises significantly above the enzyme's optimum level?

   • A) The kinetic energy of the molecules drops, preventing substrates from colliding with active sites.
   • B) The activation energy required for the reaction increases because substrate molecules are rapidly degraded.
   • C) The thermal agitation disrupts hydrogen and ionic bonds, denaturing the enzyme's active site.
   • D) The concentration of cofactors decreases as thermal energy converts them into competitive inhibitors.
5. 5.

   In an enzyme-catalyzed reaction with a fixed enzyme concentration, which outcome is observed as the substrate concentration is continuously increased?

   • A) The reaction rate increases indefinitely in direct proportion to substrate concentration.
   • B) The reaction rate decreases steadily because excess substrate acts as an allosteric inhibitor.
   • C) The reaction rate immediately drops to zero due to competitive inhibition among substrate molecules.
   • D) The reaction rate initially increases and then plateaus as the enzyme active sites become saturated.

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