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AS Biology 1.4 Enzymes and Metabolism
Most enzymes are proteins, which are capable of catalysing (speeding up) biochemical reactions and
are therefore called biological catalysts. Enzymes act on one or more compounds (called the
substrate) they may break a single substrate molecule down into simpler substances, or join two or…

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Lock and Key theory

Induced Fit

Substrate forces itself into the active site. When the products leave, the active site returns to normal.

The Turnover Number is the amount of reactions an enzyme can catalyse in a certain amount of time.

The Activation energy is the energy needed to start…

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Different enzymes work the best at different pHs, called the optimum pH. E.g. pepsin has
optimum Ph around 2.
Small changes in pH can alter enzyme activity. Large changes in pH prevent enzyme activity.

3. Substrate Concentration
1. Substrate concentration is proportional to rate of
reaction, the more substrates the…

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prevents the substrate from binding to the enzyme. E.g. cyanide is a non ­ competitive inhibitor of
cytochrome oxidase.

Increasing substrate concentration has no affect on the rate of reaction. This is because the inhibitor
binds to a different site to the substrate. E.g. cyanide as a non competitive inhibitor…

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The reading on the display is proportional to the oxygen taken up and the glucose concentration.

When a reaction occurs the electrodes pick up slight electrical changes and convert this to an electric
current. This is then amplified and displayed.


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