What the exam asks
- Explain how extreme temperatures, non-optimal pH, or salinity changes disrupt hydrogen bonds and R-group interactions, altering active site geometry and reducing catalytic efficiency.
- Predict the effects of temperature, substrate concentration, and competitive or noncompetitive inhibitors on initial reaction rates.
- Calculate initial reaction rates from product-over-time graphs and justify claims using experimental data and error bars.
Core ideas
Temperature, kinetic energy, and denaturation
- Below optimal temperature: Molecules have lower kinetic energy, moving more slowly. This reduces the frequency of successful collisions between the enzyme’s active site and the substrate, resulting in a slow reaction rate (note: cold temperatures do not denature enzymes).
- Rising toward the optimum: Increasing temperature increases molecular movement and the frequency of enzyme–substrate collisions, speeding up the reaction rate.
- Above optimal temperature (denaturation): Excessive thermal agitation disrupts weak intramolecular forces—specifically hydrogen bonds, ionic bonds, and hydrophobic interactions between R-groups—that maintain secondary, tertiary, and quaternary structure. The active site loses its specific 3D shape, the substrate can no longer bind, and catalytic efficiency drops sharply.
pH, salinity, and reversible denaturation
Enzymes have an optimal pH range matching their cellular compartment (e.g., cytosolic enzymes near pH 7.2, lysosomal enzymes near pH 4.5–5.0). Moving outside this range alters the concentration of and ions, changing the charges on acidic and basic R-groups and disrupting hydrogen bonds and ionic bonds.