Identify all the correct ways to finish the sentence,

A "competitive inhibitor" of an enzyme binds .

A. tighter than substrate

B. reversibly to the substrate-binding site

C. irreversibly to the substrate-binding site

Question

Identify all the correct ways to finish the sentence,

A "competitive inhibitor" of an enzyme binds                               .

A. tighter than substrate

B. reversibly to the substrate-binding site

C. irreversibly to the substrate-binding site

BlackTom AI · Accepted Answer

Let's break down the question and the five answer choices by evaluating what a competitive inhibitor does.
Option 1 (A and B): This choice claims that both A and B statements are true. We know B is correct—competitive inhibitors do bind reversibly to the substrate-binding site. However, A states they bind tighter than the substrate. While competitive inhibitors resemble the substrate and compete for the active site, saying they are necessarily tighter than the substrate is not a universal truth; affinity can vary and there is no general rule that they must bind tighter than the actual substrate. Therefore, A is not a guaranteed true statement, and the combined option A and B cannot be fully correct.
Option 2 (C only): This asserts that only C is true. C says the inhibitor binds irreversibly to the substrate-binding site. That is inconsistent with the fundamental definition of competitive inhibition, which involves reversible binding to the active site to block substrate access. Since C conflicts with the established mechanism, this option is incorrect.
Option 3 (A only): This asserts that only A is true. As discussed, A’s claim about binding being tighter than substrate is not a universally valid characteristic of competitive inhibitors; B’s statement about reversible binding is the correct feature. Therefore, selecting only A misrepresents the mechanism, making this option incorrect.
Option 4 (B only): This asserts that only B is true. B correctly states that competitive inhibitors bind reversibly to the substrate-binding site (the active site), competing with the substrate for access. This aligns with the standard concept of competitive inhibition and explains why the inhibitor can be overcome by increasing substrate concentration.
Option 5 (A and C): This combines A and C. Since C claims irreversible binding and A makes an uncertain claim about binding tighter than the substrate, this combination cannot be correct because competitive inhibition is characterized by reversibility (not irreversible binding) and the tighter-than-substrate claim for A is not universally valid.
In summary, the only option that consistently aligns with the accepted mechanism of competitive inhibition is the one that includes B as true and excludes the other statements as universally true.

BIOC 440 A Lecture Concept Exercise | 12

Identify all the correct ways to finish the sentence, A "competitive inhibitor" of an enzyme binds . A. tighter than substrate B. reversibly to the substrate-binding site C. irreversibly to the substrate-binding site

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