Biology: Biochemistry and Plant Physiology - Enzymes as Biological Catalysts and Factors Affecting Enzyme Activity

Enzymes are globular proteins that act as biological catalysts, which speed up chemical reactions in living organisms without being consumed in the process.

The Lock and Key Hypothesis: Enzymes have a specific 3D shape with an active site where the substrate binds. Only a substrate with a complementary shape can fit, forming an enzyme-substrate complex.

Activation Energy ($E_a$): Enzymes work by lowering the $E_a$ required for a reaction to proceed, allowing metabolic processes to occur rapidly at body temperature.

Effect of Temperature: As temperature increases, kinetic energy increases, leading to more frequent collisions between enzymes and substrates. However, beyond the optimum temperature (usually $\approx 37^\circ C$ for humans), the enzyme becomes denatured (the active site loses its shape).

Effect of pH: Every enzyme has an optimum pH (e.g., Pepsin at $pH \approx 2$, Amylase at $pH \approx 7$). Deviations from this pH can break ionic and hydrogen bonds, leading to denaturation.

Substrate Concentration: Increasing substrate concentration ($[S]$) increases the rate of reaction until all active sites are occupied (the saturation point, or $V_{max}$).