Question

mini-quiz: substrate concentration and enzymes
how is enzyme activity at varying substrate concentrations different from enzyme activity at varying temperatures or ph levels?
i. the graph for substrate concentration shows the rate levelling off when substrate concentration is high, instead of declining when not in the optimal range.
ii. when increasing substrate concentration, it is apparent that the enzyme denatures but this is not seen when increasing temperature or ph.
iii. changes in substrate concentration do not cause the enzyme to denature, but changes in temperature and ph may cause the enzyme to denature.
a. ii and iii only
b. i, ii and iii
c. iii only
d. i and iii only

Explanation:

• For statement I: When substrate concentration is high, enzyme - substrate complexes form at maximum rate (all active sites are occupied), so the rate levels off. For temperature and pH, outside the optimal range, enzyme activity declines (due to denaturation in extreme cases).
• For statement II: Increasing substrate concentration does not denature the enzyme. Enzyme denaturation can occur with extreme temperature or pH changes. So, this statement is incorrect.
• For statement III: Substrate concentration changes (within reasonable physiological ranges) do not cause denaturation. Temperature (e.g., very high temperatures) and pH (e.g., extreme acidic or basic conditions) can cause enzyme denaturation.

Answer:

D. I and III only