Q.Explain the mechanism of enzyme action.

[!TLDR]

The question asks for a full explanation of the mechanism of enzyme action, including how the active site recognises the substrate. …

The basic mechanism of enzyme action is the formation of a temporary enzyme-substrate (ES) complex. The substrate binds to a specific region of the enzyme called the active site, giving E + S -> ES; the reaction is carried out while the substrate is held in this complex; and the product is then released, freeing the enzyme so it can bind another substrate molecule and repeat the cycle: ES -> E + P. This is what allows the enzyme to speed the reaction up dramatically - by forming the ES complex, the enzyme stabilises an intermediate transition state at a lower energy level than would otherwise be needed, so the activation energy the reaction requires is greatly reduced. If potential energy is plotted against the progress of the reaction, an uncatalysed reaction must climb a tall energy barrier, whereas the same reaction in the presence of the enzyme needs only a much smaller energy input to reach the transition state and proceed to product. …

• Explaining only the ES-complex/activation-energy part of the mechanism while omitting the Lock-and-Key/Induced-Fit hypotheses, or vice versa, when the question asks for the full mechanism. …