ENZYMES

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• specific sequence of amino acids, with various intermolecular interaction, produces a pocket-like region known as an active site

1. bind with a substrate of complementary shape to result in a biochemical reaction

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   • since the pocket is of a specific shape, it recognises only substrates that can fit in properly to cause a reaction to occur
   1. lock and key mechanism
   2. little helpers
      1. coenzyme

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         • often bind TEMPORARILY to an enzyme to facilitate the catalysis e.g. complex organic compounds of vitamin
      2. prosthetic group

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         • binds PERMANENTLY to an enzyme to facilitate the catalysis e.g. Carbonic anhydrase, a metalloenzyme, contains a Zn2+ ion at the heart of the active site. Cytochrome oxidase, an enzyme involved in respiration thas the haem group
   3. inhibition

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      • occurs when the enzyme is no longer able to catalyse the reaction
      1. competitive

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         • competition of an inhibitor with the shape similar to the substrate to bind to the active site
         1. reversible

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            • can be reversed when the concentration of substrate is increased
      2. non-competitive

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         • a molecule can bind to the site other than active site (allosteric site) of an enzyme causing the shape of active site to alter and does not recognise the substrate anymore
         1. irreversible
   4. factors affecting the catalytic activity
      1. pH

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         • affects the hydrogen & ionic bond interactions between enzymes & substrates, which affects the binding activity also disrupt the shape of enzyme causing it to denature
      2. temperature

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         • the overall speed increases. However, the enzyme structure is disrupted when temperature > optimum temperature (usually 40deg C), the bonds holding the enzyme molecule in its precise shape begin to break.
      3. chemicals

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         • High or low salt concentration affects the charges on the amino acids which may alter the shape of enzyme or causes the enzyme to precipitate presence of urea will disrupt the hydrogen bonding

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• by providing an alternative pathway with a lower activation energy

1. enzyme vs inorganic catalyst
   1. more specific

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      • since its active site can only fit in substrate that has specific size & shape
   2. react at milder conditions

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      • enzymes often work optimally at body temperature (i.e.36.9deg C) and almost neutral pH
   3. capacity for regulation

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      • able to control the regulate the amount of enzymes & substrates while the biochemical reactions are on-going