Biology 4-7

Additional biology 4-7



Enzyme Structure

Enzymes- protein molecules made up of chains of amino acids.

  • They turn larger molecules into smaller ones
  • They do not get used up as they work
  • They are specific to a certain type of molecule
  • They change shape as they work.

They act as biological catalysts so they can speed up chemical reactions.

Activation energy- the minimum amount of energy particles must have to be able to react.

The reaction is more likely to happen if:

  • reacting particles bump into each other
  • increase the energy of the particle collisions
  • reduce the activation energy needed
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How an enzyme works

  • Enzymes are made of long chains

  of amino acids. The chains are 

folded to form the active site.

  • The substrate (reactant)

 binds to the enzyme to form an

enzyme-subtrate complex.

  • When the reaction is complete the

products are released and the enzyme

can be used again.

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Factors affecting enzyme action

  • Enzyme activity is affected by temperature and pH.
  • Effect of temperature on enzymes: the rate of enzyme controlled reactions increases with an increase in temperature.
  • Substrate particles are more likely to collide with enough energy to react.
  • After temperatures of about 40'C, the protein structure of the enzyme is affected by the temperature.
  • The long amino acid chains begin to unravel and the shape of the active site changes.
  • The enzyme is denatured
  • It can no longer act as a catalyst, so the rate of reaction drops dramatically.
  • Most human enzymes work best at  37'C
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Effect of pH on enzymes: A change in pH affect the forces between the different parts of the protein molecule which hold the folded chains in place.

  • If the pH changes, it interferes with the bonds/forces holding the enzyme together, changing the shape of the molecule and denaturing it.
  • All enzymes have an optimum pH, eg.
  • pepsin: used to break down proteins in the stomach and works best at pH 2.
  • amylase: found in the small intestine and works best at pH 8.
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Aerobic respiration

  • Aerobic respiration involves chemical reactions which use oxygen and sugar and release energy.
  • Glucose + oxygen → Carbon dioxide + water (energy)
  • Most reactions in aerobic respiration happen inside the mitochondria.
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