Transcript pH and enzymes in cheese making File

The Chemicals of Living Cells
©The Wellcome Trust
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The chemicals of life
All living organisms are made up of chemical substances
Reactions between these substances keep the organism
alive. They are living processes.
The sum of all the chemical reactions in an organism is
called it metabolism
Enzymes
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Enzymes are special proteins
They are present in the cytoplasm of all cells
They help to speed up the chemical reactions in the cell
There are hundreds of different enzymes but each enzyme
speeds up only one kind of reaction
For example, glucose and fructose might join up slowly to
form sucrose
glucose-
-fructose
With the right enzyme present, the reaction happens faster
glucose-
-fructose
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The molecules fit the shape of the enzyme
enzyme
substrate A
substrate B
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substrates combine temporarily with enzyme
enzyme joins substrates together
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enzyme unchanged
and ready for
next reaction
new compound released
by enzyme
Different types of enzyme reaction
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The last 4 slides show how an enzyme is involved in
combining substrates to create a larger molecule
For example, the enzyme could be building up a sucrose
molecule from glucose and fructose
An enzyme can also help to break a large molecule
into smaller molecules
For example an enzyme can split a sucrose molecule
into the smaller glucose and fructose molecules
A ‘breaking-down’ reaction
the shape of the substrate molecule
fits the enzyme shape
this is called
the active site
of the enzyme
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Intermediate stage (1)
substrate combines
temporarily with enzyme
enzyme will break
molecule here
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Intermediate stage (2)
substrate splits and
separates from enzyme
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Final break-down products
enzyme ready for
next reaction
end-products
Properties of enzymes
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Enzymes can act on only one type of
molecule
They always produce the same end products
Although they take part in the reaction, they are not
used up
Because enzymes are proteins, they are denatured by heat
or some chemicals
Denaturing involves a change of shape in the enzyme
molecule so that it cannot combine with the substrate
Individual enzymes work best at a particular temperature
and pH (acidity or alkalinity)
Enzymes can act on only one type of substrate
this substrate
cannot combine
with this enzyme
this substrate
cannot combine
with this enzyme
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Because enzymes are proteins, they are denatured by
heat or some chemicals
enzyme
denatured
by heat
enzyme +
substrate
denatured enzyme
cannot combine with substrate
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pH = % hydrogen ions
• The pH of a substance is the measure of its acidity.
• pH is measured on a scale from 1 to 14.
pH of substances
o To measure pH an indicator is used. Indicators change
colour depending on the pH of the substance they are
mixed with
pH in food production
 Yeast and bacteria grow and reproduce within specific
ranges of pH
In cheese-making sometimes bacteria are used to help
change the milk into a more solid form (coagulation).
 The bacteria produce lactic acid
 The bacteria can tolerate slightly acidic conditions
 In bread-making yeast produce carbon dioxide (CO2)
during the process of fermentation. CO2 dissolves into
water to form carbonic acid.
 Yeast cells prefer neutral environments to grow and
reproduce