What are the different classes of enzymes? Explain any two with the type of reactions they catalyse.

(N/A) $\Rightarrow$ Thousands of enzymes have been discovered, isolated, and studied.
$\Rightarrow$ Most of these enzymes have been classified into $6$ different groups based on the type of reactions they catalyse.
$\Rightarrow$ Enzymes are divided into $6$ classes, each with $4-13$ subclasses, and named accordingly by a four-digit number.
$(1)$ Oxidoreductases/dehydrogenases: Enzymes which catalyse oxidoreduction between two substrates $S$ and $S'$ e.g., $S \text{ reduced} + S' \text{ oxidised} \longrightarrow S \text{ oxidised} + S' \text{ reduced}$.
$(2)$ Transferases: Enzymes catalysing a transfer of a group, $G$ (other than hydrogen), between a pair of substrates $S$ and $S'$ e.g., $S-G + S' \longrightarrow S + S'-G$.
$(3)$ Hydrolases: Enzymes catalysing the hydrolysis of ester, ether, peptide, glycosidic, $C-C$, $C$-halide, or $P-N$ bonds.
$(4)$ Lyases: Enzymes that catalyse the removal of groups from substrates by mechanisms other than hydrolysis, leaving double bonds.
$(5)$ Isomerases: Includes all enzymes catalysing the inter-conversion of optical, geometric, or positional isomers.
$(6)$ Ligases: Enzymes catalysing the linking together of $2$ compounds, e.g., enzymes which catalyse the joining of $C-O$, $C-S$, $C-N$, $P-O$ etc. bonds.