How Temperature, pH, and Substrate Concentration Affect Enzyme Activity
- Temperature, pH, and substrate concentration, influence the rate of enzyme-catalyzed reactions.
- Understanding these effects requires exploring collision theory and denaturation.
Temperature and Enzyme Activity
- As temperature rises, molecules gain kinetic energy, moving and colliding faster.
- This increases the frequency of enzyme-substrate collisions, raising the reaction rate.
The rate of enzyme activity typically doubles for every 10°C increase in temperature, up to a certain point.
Beyond the Optimum: Denaturation
- Each enzyme has an optimum temperature where its activity is highest.
- Beyond this temperature, high temperatures cause the enzyme to denature, disrupting its structure and active site.
- This denaturation reduces or halts enzyme activity, as the enzyme can no longer bind to the substrate effectively.
- Denaturation occurs when the bonds maintaining the enzyme’s three-dimensional shape are disrupted, altering the active site.
pH And Enzyme Activity
- Enzymes have an optimum pH where the active site is in the best shape for substrate binding.
- pH affects the ionic and hydrogen bonds that maintain the enzyme's structure.
- At the optimum pH, these bonds stabilize the active site in its most functional configuration.
pH deviation: Denaturation
- If pH is too acidic or too basic, these bonds are disrupted.
- The active site changes shape, reducing or eliminating enzyme activity.
- Unlike temperature (denaturation at high levels only), pH can denature enzymes at both extremes.
- Pepsin, a digestive enzyme in the stomach, works best at a highly acidic pH of around 2.
- In contrast, trypsin, found in the small intestine, has an optimum pH of about 8.
- Unlike temperature (denaturation at high levels only), pH can denature enzymes at both extremes.
- This is because temperature is about energy breaking bonds, while pH is about charge disruption affecting bonds.
- So, charge can go wrong in two directions (too many or too few H⁺ ions), but energy only breaks bonds when there's too much of it.
Substrate Concentration And Enzyme Activity
- As substrate concentration increases, enzyme-substrate collisions become more frequent.
- Reaction rate increases because more active sites are occupied.
At low substrate concentrations, most active sites are unoccupied, so increasing the concentration significantly boosts the reaction rate.
Saturation Point: Maximum Activity
- Eventually, a point is reached where all active sites are occupied.
- This is known as the saturation point.
- Further increases in substrate concentration do not increase the rate because enzymes are working at full capacity.
- Imagine a factory with 10 machines (enzymes) and 5 workers (substrates).
- Adding more workers increases productivity until all machines are occupied.
- Beyond that, extra workers have no effect.
Interpreting Graphs
- Temperature vs. activity: Bell-shaped curve. Increases to optimum, then decreases due to denaturation.
- pH vs. activity: Bell-shaped curve. Highest at optimum pH, decreases on either side due to structural changes.
- Substrate concentration vs. activity: Hyperbolic curve. Increases then plateaus at saturation.
- What happens to molecular movement as temperature increases?
- Why does increased molecular movement increase enzyme activity?
- Why can pH cause denaturation at both high and low values, but temperature only causes it at high values?
- Describe the shape of a substrate concentration vs. enzyme activity graph.
