Enzymes Revision

Notes on the effect of temperature, pH, concentration and inhibitors

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Enzymes & Temperature
Have Natural Kinetic Energy
When Heated this energy increase
Which enables collisions to happen more frequently
Too much heat makes the enzyme vibrate too much and breaks the hydrogen & Ionic
bonds. Denaturing the Enzyme and rapidly decreasing the rate of reaction until it
Different Enzymes have different optimum temperatures usually between 40 and
Too little heat does not denature the Enzyme.
Katie Blake

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Enzymes & pH
Increasing and decreasing the pH, Increases and decreases the concentration of
Hydrogen Ions around the Enzyme.
This can alter the tertiary structure and change the shape of the active site.
This changes the rate of and enzyme-controlled reaction.
Each enzyme has a different optimum pH.
A pH that is too low, denatures the enzyme
As well as this, a pH that is too high also denatures the enzyme.…read more

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Enzymes and substrate concentration
The rate of an enzyme-catalysed reaction depends on the concentrations of enzyme and
As the concentration of either is increased the rate of reaction increases.
For a given enzyme concentration, the rate of reaction increases with increasing substrate
concentration up to a point, above which any further increase in substrate concentration
produces no significant change in reaction rate.
This is because the active sites of the enzyme molecules at any given moment are virtually
saturated with substrate.…read more

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Enzymes - Inhibitors
An enzyme inhibitor is any substance or molecule that slows down the rate of an
enzyme-controlled reaction, by affecting the enzyme molecule in some way.
Competitive Inhibitors
Have a similar shape to the substrate molecules
They occupy the active site.
Forming an enzyme-inhibitor complex.
This prevents the substrate from binding and stops the reaction.
Non-competitive inhibitors
Attach to the allosteric site of an enzyme.
This distorts the shape of the active site.…read more

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Enzymes - Coenzymes & Prosthetic Groups
Some enzymes only catalyse reactions id another non-protein substance is present. These
are known as Cofactors.
Coenzymes are small, organic, non-protein molecules that bind for a short period of time to
the enzyme.
They Bind either Just before a reaction takes place, or at the same time as the substrate.
They get changed slightly by taking place in a reaction. However they are Recycled back to
take part in the reaction again.…read more

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Interfering with Enzymes - Poisons & Drugs
Many Deadly Poisons Inhibit or over activate the enzymes.
Potassium Cyanide inhibits cell respiration, It in non-competitive. And decreases the
production of ATP, also due to only being able to respire anaerobically lactic acid builds up in
the blood.
Replacement Enzymes are used to treat some medical conditions, i.e. cystic fibrosis. They
are packaged in acid-resistant coating, to avoid being destroyed in the stomach and
swallowed.…read more


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