Digestive Enzymes

• Enzymes catalyse (speed up) chemical reactions.
• Enzymes are large protein molecules and they have a groove on their surface called the active site.
• The active site of an enzyme is where the substrate attaches

  
• The enzyme breaks down the substrate into the products.
• If the substrate does not fit into the active site, the enzymes cannot break it down.
• Enzymes are specific. The substrate must fit perfectly into the active site of the enzyme (the lock and key theory).
• Proteins are broken down by enzymes called proteases.
• Proteins are long chains of chemicals called amino acids
• When we digest proteins, the protease enzymes convert the protein back to the individual amino acids, which are then absorbed into the bloodstream.
• When the amino acids are absorbed by the body cells, they are joined together in a different order to make human proteins.
• Starch consists of a chain of glucose molecules.
• Carbohydrates are broken down by enzymes called carbohydrase. I the case of starch this is called amylase.
• When carbohydrates like starch are digested we produce simple sugars.
• Amylase if found in the saliva and pancreatic fluid.
• A lipid molecule consists of a molecule of glycerol attached to three molecules of fatty acids.
• Lipid molecules are digested by the enzyme lipase. This produces glycerol and fatty acids.
• We find lipase in the pancreatic fluid and the small intestine.
• Bile is made in the liver and it is stored in the gall bladder.
• Bile helps to speed up the digestion of lipids but bile is not an enzyme.
• Bile converts large lipid droplets into smaller droplets.

  
• Bile emulsifies the lipid.
• Bile massively increases the surface area of the droplets by slipping them up.
• Once the droplets have a larger surface area, this increases the rate of lipid breakdown by lipase.
• Bile is alkaline. This allows it to neutralise stomach acid, creating alkaline conditions in the small intestine.