Enzyme-Substrate Lock and Key Fit

Steps:

• Examine the enzyme's active site shape in the diagram.
• Compare each substrate option's molecular structure to the active site.
• Identify the substrate that matches the active site's contour exactly.
• Select the option with the precise complementary shape.

Why A is correct:

• Option A has a structure that perfectly complements the enzyme's active site, following the lock and key model where substrate binds specifically to the enzyme's shape.

Why the others are wrong:

• B has a mismatched protrusion that prevents binding.
• C lacks the required indentation for the active site groove.
• D is too bulky and cannot fit into the active site pocket.

Final answer: A