Biology – 7.2 Human nutrition – alimentary canal | e-Consult

Enzyme Action: The Lock-and-Key Model

Enzymes are highly specific biological catalysts. This specificity arises from the unique three-dimensional shape of the enzyme, particularly the active site. The active site is a region on the enzyme where the substrate (the molecule the enzyme acts upon) binds. The active site has a specific shape that complements the shape of the substrate, much like a key fits into a lock. This complementary shape allows the substrate to bind to the active site, forming an enzyme-substrate complex.

The enzyme-substrate complex facilitates the chemical reaction. The enzyme lowers the activation energy required for the reaction to occur, speeding up the rate of digestion. The substrate is converted into products, and the products are released from the active site. The enzyme remains unchanged and is free to catalyze another reaction.

Factors Affecting Enzyme Activity:

• Temperature: Enzymes have an optimal temperature at which they work best. Below this temperature, enzyme activity is slow. Above this temperature, the enzyme denatures (loses its shape), and activity stops.
• pH: Enzymes also have an optimal pH. Extreme pH values can denature the enzyme. Different enzymes have different optimal pH ranges.
• Substrate Concentration: As substrate concentration increases, enzyme activity increases until all the enzyme molecules are saturated with substrate. Beyond this point, increasing substrate concentration will not further increase enzyme activity.
• Enzyme Concentration: Increasing the concentration of enzyme molecules increases the rate of reaction, assuming there is sufficient substrate available.