AS Biology Enzymes

Enzymes are biological catalysts that speed up chemical reactions such as digestion and respiration. They can be intracellular or extracelluar in places like the digestive system or blood
1. Reduce amount of activation energy needed , therefore usually lowering the temperature needed and speeding the rate of reaction up
  1. Substrates binding to an active site forms enzyme- substrate complex's that then lower the activation energy
    1. Joins two substrate molecules by an enzyme which reduces repulsion allowing them to bond more easliy
    2. Fitting into active sites puts strain on substrate bonds which means it can be broken down quicker in breakdown reactions
Globular proteins with active sites specific to the shape of their substrates , these are determined by the tertiary structure. Enzymes only work when the substrate fits and binds into the active site , they are largely specific
Enzyme action models
1. Lock and Key model
  1. Substrate fits into enzyme like a key fits into a lock
2. Induced fit model
  1. Substrate has to be the right shape but also makes the active site change to the right shape as well.
Factors affecting enzyme activity
1. Increased temperature makes molecules vibrate more and collisions will increase (speeding up the rate of reaction). However above a certain temperature the bonds break that hold the enzyme together and the active site changes shape meaning the substrate no longer fits and the enzyme denatures
2. Enzymes have an optimum pH depending on where they work in the body. H+ and OH- ions can interfer with bonds keeping the tertiary structure in place , changing the active site and denaturing the enzyme.
3. Enzyme concentration and substrate concentration increasing can increase collisions and rate of reaction as more active sites are likely to be filled. There is a saturation point where there are no more active sites or substrates to fill them available.
4. Experiments to measure enzyme controlled reactions
  1. Measuring how fast the product appears by using catalase to break down hydrogen peroxide into water/oxygen and measure gas given off
  2. Disappearance of substrate by breaking starch into maltose using amaylase
Enzyme inhibitors
1. Competitive inhibitors are shaped like the substrate, they compete with the substrate molecule to bind to the active site. No reaction occurs though, they just block the active site so the reaction is slowed down.
2. Non competitive inhibitors bind to the enzyme but not on the active site. It causes the substrate to change shape , so no competition is needed because the substrate can no longer fit
3. Inhibitors are reversible or irreversible , covalent bonds mean it is irreversible and weak hydrogen bonds mean its reversible
  1. Cyanide is an irreversible inhibitor of cytochrome C oxidase used in respiration and Malonate/ Arsenic have similar effects
  2. Drugs work by inhibiting enzymes too. Antiviral drugs inhibit reverse transcriptase which is a catalyst for DNA replication. Antibiotics also inhibit transpeptidase which prevents proteins forming on cell walls and allows cells to burst to kill bacteria
Cofactors and Coenzymes
1. Non protein substances that allow enzymes to work in binding substrate and enzyme together. Manganese ions are an example , they aren't part of the reaction so they don't get used up
2. The organic molecules (coenzymes) actually take part in the reaction and act as chemical groups/carriers that are recycled through the reactions

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AS Biology Enzymes

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	Created by Megan Tarbuck almost 9 years ago