Enzymes
Science Practicals: GCSE, topic 1.1.5
Enzymes
Enzymes increase the speed of reactions. They are often called biological catalysts. The active site of an enzyme is very important:
Active site
- To catalyse (speed up) a reaction, the reacting chemical (substrate) must bind to the enzyme's active site.
- The active site will only fit specific substrates.
Lock and key
- The active site is like a lock and the substrate is like a key.
- In the same way, there is usually only one enzyme for every substrate (or one key for each lock).
Factors Affecting the Rate of Enzyme Action
The factors that affect the rate (speed) of enzyme action are:
Temperature
- Increasing the temperature of a working enzyme initially increases the reacting activity.
- Enzymes have an optimum temperature. Once this temperature is reached, the activity decreases.
- Past a certain temperature, the active site changes shape, and the enzyme is denatured (loses its catalytic activity).
pH (measure of acidity)
- Enzymes have an optimum pH (measure of acidity).
- If the pH changes away from the optimum pH, then the enzyme activity decreases.
- If the pH is too low or too high, then the enzyme is denatured and will not function.
Substrate concentration
- Increasing the substrate concentration will increase the rate of activity to a certain point until it levels off.
- This is because if there are more substrate molecules available for the enzyme to bind to, the rate increases.
- But once there are enough substrate molecules for all the enzymes to bind to, increasing the substrate concentration any more will have no effect on the rate of activity.
Test yourself on Enzymes
What is another name for an enzyme?
Which of the following describe an enzyme's active site?
What happens to enzymes when pH is very high?