Enzyme-Substrate Complex Formation — NEET Biology

Correct answer: A — S1 and S2 only

The core concept here relates to the nature of enzyme-substrate interaction and the catalytic cycle. Let's evaluate each statement based on NCERT text: S1: "The binding of the substrate induces the enzyme to alter its shape, fitting more tightly around the substrate." This statement is correct. S2: "This complex is short-lived and dissociates into its product(s) P and the unchanged enzyme with an intermediate formation of the enzyme-product complex (EP)." This statement is correct, as EP is explicitly mentioned as an intermediate. S3: The NCERT states that the enzyme is "unchanged enzyme" after product release and is "ready to bind to another molecule of the substrate and run through the catalytic cycle once again." This means enzymes are not consumed. Thus, statement S3 is incorrect. S4: NCERT states, "An active site of an enzyme is a crevice or pocket into which the substrate fits." However, it also states, "The binding of the substrate induces the enzyme to alter its shape, fitting more tightly around the substrate." This indicates that the fit is not always perfect initially and involves induced changes. The word 'always' makes this statement incorrect. S5: NCERT explicitly states, "There is thus, an obligatory formation of an ‘ES’ complex." This means the formation is essential, not optional. Thus, statement S5 is incorrect. Therefore, only S1 and S2 are correct. The final answer is A, as S1 and S2 correctly describe aspects of enzyme-substrate interaction and the catalytic cycle. Concept Recap: Enzymes bind substrates at active sites to form transient enzyme-substrate and enzyme-product complexes, facilitating reactions without being consumed, often involving induced fit.