Enzyme Structure and Substrate Conversion — NEET Biology

Correct answer: D — S1, S3, S4 and S5 are correct

Let's evaluate each statement regarding the nature of enzyme action: S1. The substrate binds to the active site of the enzyme, fitting into it, and this binding induces the enzyme to alter its shape, fitting more tightly around the substrate. This statement is correct, as described in step 2 of the catalytic cycle. S2. The formation of the enzyme-substrate (ES) complex is a transient phenomenon, not permanent and irreversible. The complex quickly dissociates into product(s) and the unchanged enzyme. So, this statement is incorrect. S3. Enzymes lower the activation energy of a reaction, making the transition of substrate (S) to product (P) more easy, thus accelerating the reaction rate. This statement is correct, as explained in Section 9.8.2. S4. After releasing the products, the enzyme remains unchanged and is ready to bind to another molecule of the substrate, running through the catalytic cycle once again. Thus, the enzyme is not altered and is reused. So, this statement is incorrect. S5. The active site of the enzyme, in close proximity to the substrate, is where the chemical bonds of the substrate are broken and new enzyme-product complex is formed, facilitating the unique chemical conversion. This statement is correct. Based on the analysis, statements S1, S3, and S5 are correct. Therefore, option B is the correct answer. Option A is incorrect because S2 is false. Option C is incorrect because S2 and S4 are false. Option D is incorrect because S4 is false. This question assesses the core understanding of the steps and principles governing enzyme catalysis, emphasizing the transient nature of complexes and the role of activation energy.