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.

1Biology

1.1Practicals

1.1.1Microscope & Bacteria

1.1.2Bacteria

1.1.3Osmosis Tests

1.1.4Osmosis & Food Tests

1.1.5Enzymes

1.1.6Enzymes 2

1.1.7Photosynthesis & Plant Responses

1.1.8Photosynthesis Experiments

1.1.9Reaction Time

1.1.10Quadrats

1.1.11Decay

2Chemistry

2.1Practicals

2.1.1Salts

2.1.2Neutralisation

2.1.3Titration

2.1.4Electrolysis

2.1.5Electrolysis 2

2.1.6Rate of Reaction

2.1.7Rate of Reaction 2

2.1.8Chromatography

2.1.9Identifying Gases

2.1.10Identifying Gases 2

2.1.11Identifying Ions

2.1.12Carbonates, Halides & Sulfates

2.1.13Flame Emission Spectroscopy

2.1.14Water Purification

2.1.15Water Purification 2

3Physics

3.1Practicals

3.1.1Specific Heat Capacity

3.1.2Thermal Capacity & Insulation

3.1.3Latent Heat

3.1.4Resistance & Current

3.1.5Resistance & Current 2

3.1.6Density

3.1.7Density 2

3.1.8Force & Extension - Springs

3.1.9Waves - Ripple Tank

3.1.10Light

3.1.11Light Reflection & Refraction

3.1.12Radiation

3.1.13Radiation 2

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