Final answer:
The structural feature of enzymes that requires the presence of a coenzyme for redox reactions to occur is the active site. Coenzymes bind to this active site, forming a holoenzyme that is necessary for the enzyme's catalytic activity. Competitive inhibitors structurally resemble the substrate and compete for the active site.
Step-by-step explanation:
Structural Feature of Enzymes in Redox Reactions
Enzymes that catalyze redox reactions often require a coenzyme to function. This is because some enzymes lack the necessary components to stabilize their reactive intermediates. Coenzymes often serve as electron carriers, providing or accepting electrons necessary for the redox reactions.
The structural feature of enzymes that catalyzes redox reactions and requires the presence of a coenzyme is the active site. This is where the substrate binds, and the reaction occurs. If a coenzyme is necessary for the enzyme to function, it must bind to the enzyme’s active site to form a complete and active enzyme, known as a holoenzyme.
Regarding the other options provided in the question, coenzymes may be considered as a type of cofactor, but the latter generally refers to a broader group of substances that can include metal ions and other small molecules. The substrate is the specific molecule upon which an enzyme acts, and an inhibitor is a compound that binds to an enzyme to decrease its activity. In the case of competitive inhibitors, they most structurally resemble the substrate (C). They compete with the substrate for the active site, preventing the actual substrate from binding and thereby slowing down the reaction or stopping it entirely.