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Enzymes (biological catalysts)

Enzymes are biological catalysts that control and direct all the

reactions that occur in plant cells. They may be defined as organic catalysts

produced by living cells but independent on the cells in their action i.e. they

can catalyze reactions in vitro (in tubes).

Zymase

Glucose  Alcohol + CO2

Yeast

Substrate mix. of enzymes End product

Enzyme structure:

1. Enzymes are generally globular proteins with characteristic three
dimensional shapes.

2. The active site is the binding site for the enzyme’s substrate, so
anything that alters the shape of the active site will affect enzyme
activity The specific action of an enzyme with a single substrate can
be explained using a Lock and Key analogy (Figure 10). In this
analogy, the lock is the enzyme and the key is the substrate. Only the
correctly sized key (substrate) fits into the key hole (active site) of
the lock (enzyme).

3. Enzymes classified according to their structure into:
i. Apoenzmes (simple enzymes) which are composed of protein
only.
ii. Holoenzmes (complex enzymes) which are composed of
protein portion (apoenzymes) and a relatively small organic
and / or inorganic molecules known as cofactor.

4. Most enzyme are holoenzymes.

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