Which of the following sequences most correctly represents the results of a reaction involving an enzyme? (A) $P_1 + S \rightarrow P_2 + E$ (B) $S + E \rightarrow P_1 + P_2$ (C) $P_1 + P_2 + E \rightarrow S + E$ (D) $S + E \rightarrow P_1 + E$ - HSC - SSCE Biology - Question 10 - 2004 - Paper 1

To determine which sequence correctly represents an enzymatic reaction, we need to consider the general mechanism of enzyme action. Enzymes typically bind to substrates to form products. The most common reaction pathway can be summarized as follows:

1. An enzyme (E) binds to a substrate (S).
2. This enzyme-substrate complex then converts the substrate into products, with the enzyme remaining unchanged at the end.

Among the provided options, the correct representation should show the enzyme interacting with a substrate to produce one or more products while regenerating the enzyme itself.

Upon analyzing the options:

• Option A: $P_1 + S \rightarrow P_2 + E$ does not correctly depict the initial binding of E.
• Option B: $S + E \rightarrow P_1 + P_2$ correctly shows a substrate interacting with an enzyme to yield products but does not maintain the enzyme form correct.
• Option C: $P_1 + P_2 + E \rightarrow S + E$ shows products converting back to a substrate, which is incorrect for a standard reaction pathway.
• Option D: $S + E \rightarrow P_1 + E$ properly represents an enzyme (E) acting on a substrate (S) to produce a product (P_1) while the enzyme is left unchanged.

Therefore, the best and correct answer is Option D.