Ibuprofen as Competitive Inhibitor

Steps:

• Identify key detail: Ibuprofen binds reversibly to the enzyme's active site, blocking substrate access.
• Recall definitions: Competitive inhibition occurs when inhibitor and substrate vie for the active site; non-competitive binds elsewhere, altering enzyme shape.
• Match to example: Binding to active site means competition with substrate, not shape alteration at another site.
• Eliminate mismatches: Reasons in B, C, D describe non-competitive traits or incorrect mechanisms.

Why A is correct:

• Competitive inhibition definition: Inhibitor binds active site, preventing substrate binding; ibuprofen fits as it reversibly occupies the site, mimicking substrate competition.

Why the others are wrong:

• B: Non-competitive inhibitors bind allosteric sites to alter shape, not the active site.
• C: Blocking active site defines competitive, not non-competitive inhibition.
• D: Substrate shape similarity is a competitive trait, but option wrongly labels it non-competitive.

Final answer: A