Rates of Reaction

Catalysts - Enzymes - Temperature and pH.
What is an Enzyme?

An enzyme is a protein molecule.
are used by living cells as catalysts.
Enzymes are very specific catalysts.
This means that one particular enzyme will act as a
catalyst for one particular reaction but nothing else.

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

A graph of enzyme activity plotted against temperature
is shown below. Enzyme activity is a
measure of how well an enzyme works as a catalyst.
Graph showing Enzyme Activity against Temperature

Above 40 °C, the enzyme begins to stops working.
Above this temperature the
shape of the enzyme changes 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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