enzymes

• enzyme 


  speed up chemical reactions by acting as biological catalysts.
• intracellular enzymes 


  within cells
• extracellular enzymes 


  outside cells
• example of a intracellular enzyme

  Catalase is an enzyme that works inside cells to catalyse the breakdown of hydrogen peroxide to harmless oxygen and water. Hydrogen peroxide (H,O,) is the toxic by-product of several cellular reactions. If left to build up, it can kill cells.
• example of extracellular enzymes

  • Amylase and trypsin both work outside cells in the human digestive system.
  • Amylase is found in saliva. It's secreted into the mouth by cells in the salivary glands. It catalyses the hydrolysis of starch into maltose in the mouth.
  • Trypsin catalyses the hydrolysis of peptide bonds - turning big polypeptides into smaller ones (which then get broken down into amino acids by other enzymes). Trypsin is produced by cells in the pancreas and secreted into the small intestine.
• what type of proteins are enzymes

  Enzymes are globular proteins.
• what is an active 


  part of the enzyme where the substrate molecules bind to. The active site has a specific shape, which is determined by the enzyme's tertiary structure
• For the enzyme to work, the substrate has to be complimentary to the enzymes active site. If the substrate shape doesn't match the active site, the reaction won't be catalysed. This means that enzymes are very specific and work with very few substrates- usually only one. When a substrate binds to an enzyme's active site, an enzyme-substrate complex is formed.
• activation energy 


  a certain amount of energy needs to be supplied to the chemicals before the reaction will start.
• Enzymes reduce the amount of activation energy that's needed, making reactions happen at a lower temperature than they could without an enzyme. This speeds up the rate of reaction.
• how enzymes lower activation energy:

  • If two substrate molecules need to be joined, attaching to the enzyme holds them close together, reducing any repulsion between the molecules so they can bond more easilv.
  • If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate. This strain means the substrate molecule breaks up more easily.