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Enxymes are biological catalysts which help speed up useful chemical reactions in the body.

Enzymes are all proteins; all proteins are made up of amino acids- these are folded into unique shapes which enzymes need to do their job.

proteins also act as structural components of tissue; eg hormones and antibodies.


  1. chemical reactions: joined together or split apart
  2. substrate: a molecule that is changed in a reaction
  3. every enzyme has an active site which a substrate joins.
  4. enzymes only usually speed up one reaction this is because a substrate has to be the correct shape to fit into an active site.
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Enzymes and the right temperature

changing the temperature tends to speed up a reaction howver cells get damaged past a certain limit.

  • bonds holding the enzyme together begin to denature if the tempertaure gets too high.
  • enzymes in the body usually work best around 37 degrees
  • PH also interferes with the reaction of enxymes as if it is too high or low the cell will become damaged or denatured
  • optimum PH (state at which enxymes work best): often neutral PH7 however some enzymes like pepsin which breaks down protein in the stomach works best aroun ph2 (well suited to acidic conditions).
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enzymes and digestion

digestive enzymes break down big molecules into smaller ones.

  1. starch proteins and fats (big molecules) are too big to pass through the digestive system
  2. sugars, amino acids, glyceral and fatty acids are smaller molecuse so can pass through the digestive system.

bile neutralises the stomach acid and emulsifies fats.

  • bile (produced in the liver) stored in the gall bladder and released in the small intestine
  • hydrochloric acid in the stomach makes the ph too acidic for enzymes in the small intestine to work.
  • Bile is alkaline so neutralises the acid and makes conditions in the small intestine best for enzymes to work at.
  • it emulsifies fats breaking it down into tiny droplets giving a much bigger surface area of fat for the enzymes to work on making digestion faster.
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