Q.Explain the mechanism of enzyme action.

Enzymes work by binding substrate at a specific active site, forming a transient ES complex that lowers the activation energy needed for the reaction, and are released unchanged to catalyse further reactions.

Active site: Every enzyme has a specific three-dimensional region called the active site, into which the substrate molecule fits. Only a small portion of the enzyme's surface directly participates in catalysis.

Step 1 — Formation of the enzyme-substrate (ES) complex:

The substrate binds to the active site of the enzyme, forming a temporary enzyme–substrate complex. Historically this was described by:

• Lock-and-key model (Emil Fischer): the active site has a rigid shape that exactly matches the substrate, like a lock accepting only its specific key.
• Induced-fit model (Koshland) — the currently accepted model: the active site is flexible, and binding of the substrate induces a conformational change in the enzyme, allowing the active site to mould itself around the substrate for tighter binding.

Step 2 — Catalysis / conversion to product:

Within the ES complex, the enzyme brings reacting groups into proximity, strains particular bonds, and provides an alternative reaction pathway with much lower activation energy than the uncatalysed reaction. This dramatically increases the rate of the reaction.

Step 3 — Release of product: …