Factors Affecting the Rate of Enzyme Activity (Leaving Cert Biology): Revision Notes

Factors Affecting the Rate of Enzyme Activity

What factors affect the rate of enzyme action?

1. Temperature
2. pH
3. Enzyme inhibitors

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1. Temperature

• All enzymes have an optimum temperature, which is the temperature at which they work best.
• At 0°C, water freezes, and enzyme and substrate molecules cannot move. The enzyme action rate is zero.
• As the temperature rises, molecules move faster. This causes enzymes and substrates to collide more often, which speeds up reactions.
• As temperature increases, the rate of enzyme action also increases.
• Above a certain temperature, the enzyme's shape begins to change. The rate of enzyme action decreases. In humans, this happens above 37°C.
• At very high temperatures, the enzyme's active site changes permanently and the enzyme stops working. This is called denaturation.
• The optimum temperature for plant enzymes is between 25°C and 35°C.

2. pH

• All enzymes have an optimum pH, which is the pH at which they work best.
• The pH scale ranges from 0 to 14.
  • pH below 7: Acidic
  • pH 7: Neutral
  • pH above 7: Alkaline
• Many enzymes work best between a pH of 6 and 8.
• Outside this range, the enzyme becomes denatured. The active site changes shape permanently.
• A buffer solution is used to keep the pH constant in experiments.
• For example, a buffer 5 solution keeps the pH at 5.

3. Enzyme Inhibitors

• Cyanide blocks enzymes involved in respiration.
• Heavy metals like mercury and lead.
• Nerve gases like sarin attack enzymes involved in transmitting nerve impulses.

Experiments

There are three experiments related to this section. Check out our experiment notes:

1. To investigate the effect of pH on enzyme activity
2. To investigate the effect of temperature on enzyme activity
3. To investigate the effect of denaturation by heat on enzyme activity