NEET 2025 Botany Question 117 Solution

Enzymes are divided into 6 functional classes (Classes 1 through 6) based on the type of reaction they catalyze:

• • Class 1: Oxidoreductases/dehydrogenases catalyze oxidation-reduction between two substrates $S$ and $S'$ ($S_{\text{reduced}} + S'_{\text{oxidized}} \rightarrow S_{\text{oxidized}} + S'_{\text{reduced}}$).
• • Class 2: Transferases catalyze the transfer of a chemical group, $G$ (other than hydrogen), between a pair of substrates $S$ and $S'$ ($S - G + S' \rightarrow S + S' - G$).
• • Class 3: Hydrolases catalyze the hydrolytic cleavage of ester, ether, peptide, glycosidic, C-C, C-halide, or P-N bonds.
• • Class 4: Lyases catalyze removal of groups from substrates by mechanisms other than hydrolysis, forming double bonds.
• • Class 5: Isomerases catalyze interconversion of optical, geometric, or positional isomers.
• • Class 6: Ligases catalyze the linking together of two compounds (e.g. C-O, C-S, C-N, P-O bonds) coupled with ATP hydrolysis.

The given reaction: $S - G + S' \rightarrow S + S' - G$, where $G$ is a chemical group other than hydrogen (such as methyl, phosphate, or amino group). Group $G$ is transferred directly from donor substrate $S$ to acceptor substrate $S'$. This is the canonical defining reaction of Transferases.

The enzyme class is Transferase, corresponding to Option (3).