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Project Report on pH - Acidity and Basicity
pH measures the Acidity and Basicity of a solution. It is a measure of the
Hydrogen Ion (H+) concentration, and therefore a good indicator of the
Hydroxide Ion (OH-) concentration. It ranges from pH1 to pH14. Lower pH values
mean higher H+ concentrations and lower OH- concentrations.
Acid solutions have pH values below 7, and Basic solutions (alkalis are
bases) have pH values above 7. De-ionised water is pH7, which is termed
H+ and OH- Ions are charged and therefore interfere with Hydrogen and
Ionic bonds that hold together an enzyme, since they will be attracted or
repelled by the charges created by the bonds. This interference causes a
change in shape of the enzyme, and importantly, its Active Site.
Different enzymes have different Optimum pH values. This is the pH value
at which the bonds within them are influenced by H+ and OH- Ions in such a way
that the shape of their Active Site is the most Complementary to the shape of
their Substrate. At the Optimum pH, the rate of reaction is at an optimum.
Any change in pH above or below the Optimum will quickly cause a decrease
in the rate of reaction, since more of the enzyme molecules will have Active
Sites whose shapes are not (or at least are less) Complementary to the shape
of their Substrate.
Small changes in pH above or below the Optimum do not cause a permanent
change to the enzyme, since the bonds can be reformed. However, extreme
changes in pH can cause enzymes to Denature and permanently lose their
Enzymes in different locations have different Optimum pH values since
their environmental conditions may be different. For example, the enzyme
Pepsin functions best at around pH2 and is found in the stomach, which
contains Hydrochloric Acid (pH2).
Changing the Enzyme and Substrate concentrations affect the rate of
reaction of an enzyme-catalyzed reaction. Controlling these factors in a cell
is one way that an organism regulates its enzyme activity and so its
Changing the concentration of a substance only affects the rate of
reaction if it is the limiting factor: that is, it the factor that is stopping
a reaction from preceding at a higher rate.
If it is the limiting factor, increasing concentration will increase the
rate of reaction up to a point, after which any increase will not affect the
rate of reaction. This is because it will no longer be the limiting factor and
another factor will be limiting the maximum rate of reaction.
As a reaction proceeds, the rate of reaction will decrease, since the
Substrate will get used up. The highest rate of reaction, known as the Initial
Reaction Rate is the maximum reaction rate for an enzyme in an experimental
Increasing Substrate Concentration increases the rate of reaction. This is
because more substrate molecules will be colliding with enzyme molecules, so
more product will be formed.
However, after a certain concentration, any increase will have no effect
on the rate of reaction, since Substrate Concentration will no longer be the
limiting factor. The enzymes will effectively become saturated, and will be
working at their maximum possible rate.
Increasing Enzyme Concentration will increase the rate of reaction, as
more enzymes will be colliding with substrate molecules.
However, this too will only have an effect up to a certain
concentration, where the Enzyme Concentration is no longer the limiting
Project report Chemical Reactions of Enzymes
Project Report on pH - Acidity and Basicity of Enzymes
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