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STD 11 - 9. Biomolecules — BIOLOGY STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceBIOLOGYSTD 11 - 9. Biomolecules1 Mark
MCQ
Which one of the following statements is incorrect?
  • A
    The competitive inhibitor does not affect the rate of breakdown of the enzyme­substrate complex.
  • ✓
    The presence of the competitive inhibitor decreases the $K_m$ of the enzyme for the substrate.
  • C
    A competitive inhibitor reacts reversibly with the enzyme to form an enzyme­ inhibitor complex.
  • D
    In competitive inhibition, the inhibitor molecule is not chemically changed by the enzyme.
✓

Answer

Correct option: B.
The presence of the competitive inhibitor decreases the $K_m$ of the enzyme for the substrate.
b
(b) : Competitive inhibition is a reversible inhibition where inhibitor competes with the normal substrate for the active site of enzyme. A competitive inhibitor is usually chemically similar to the normal substrate and therefore, fits into the active site of an enzyme and binds with it. The inhibition is thus due to substrate analogue. The enzyme, now cannot act upon the substrate and reaction products are not formed.

$E.g.$, the activity of succinate dehydrogenase is inhibited by malonate. $K_m$ value or Michaelis constant is defined as the substrate concentration at which half of the enzyme molecules are forming enzyme substrate $(ES)$ complex, or concentration of the substrate when the velocityof the enzyme reaction is half the maximal possible. A smaller $K_m$ value indicates greater affinity of the enzyme for its substrate, hence, shows a quicker reaction. The competitive inhibitor decreases the affinity of enzyme for substrate, thus increases the $K_m$ value.

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