Digestive Enzymes

• Large food molecules are digested by enzymes into smaller molecules and these products of digestion are then absorbed into the bloodstream.
• Enzymes catalyse (speed up) chemical reactions.
• The active site is where the substrate attaches to.
• The enzyme now breaks down the substrate into the products.
• If the substrate does not fit perfectly into the active site, the enzyme cannot break down this substrate.
• Enzymes are specific. The substrate must fit perfectly into the active site (the lock and key theory).
• Proteins are broken down by enzymes called proteases and we find these in the stomach, pancreas and small intestine.
• Proteins are long chains of chemicals called amino acids.
• When we digest the 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 (type of carbohydrate) consists of a chain of glucose molecules.
• Carbohydrates are broken down by enzymes called carbohydrases. In the case of starch this is called amylase.
• When carbohydrates like starch are digested, we produce simple sugars.
• Amylase is found in the saliva and pancreas.
• 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.
• • Bile is made in the liver and it is stored in the gallbladder.
  • 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. This massively increases the surface area of the lipid droplets.
• This increases the rate of lipid breakdown by lipase.
• • Bile is also alkaline. This allows it to neutralise stomach acid, creating alkaline conditions in the small intestine.
  • This increases the rate of lipid digestion by lipase.