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Rates of Reaction

Catalysts  -  Enzymes  -  Temperature and pH.

What is an Enzyme?

Enzymes are catalysts that are produced by living cells.
An enzyme is a protein molecule.

Enzymes are very specific catalysts. This means that
one particular enzyme will act as a
catalyst for one particular reaction but nothing else.

What are the Optimum Conditions for an Enzyme?

An enzyme will work best at a particular temperature and pH,
called its optimum conditions. Enzymes usually work
best in warm conditions (around 35 to 40 °C) unlike chemical
catalysts which often work best when they are very hot.

What is Enzyme Activity?

Enzyme activity is a measure of how well (how efficiently)
an enzyme works as a catalyst. A graph of
enzyme activity plotted against temperature is shown below. 

The enzyme in the graph above works most efficiently as
a catalyst at 40 °C . This is the optimum temperature
for this enzyme. Above 40 °C the enzyme begins to work
less efficiently as a catalyst because the shape of the
enzyme molecule starts to change and it is said to denature.

A graph of enzyme activity against pH would have
a similar shape but the peak (the optimum conditions)
would be at a different pH for different enzymes.

Pepsin in the stomach works best at pH = 2.
Amylase in the mouth works best at pH = 7.

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