Enzymes and digestion

• Enzymes are proteins that function as biological catalysts, speeding up the rate of reactions without being used up, including carbohydrase (amylase), lipase and protease.
• The lock and key model is used to illustrate substrate specificity.
• Temperature, pH, enzyme concentration and inhibitors affect the action of enzymes, with low temperature causing reduced rates of collision between substrate and enzyme, the maximum rate of reaction as the optimum, and denaturation occurring increasingly at levels above the optimum, which is explained as an irreversible change to the shape of the active site that inhibits enzyme action.
• Inhibitors are molecules that fit the active site but are not broken down.
• Enzymes are needed to break down (digest) large, insoluble molecules into small, soluble ones that can then be absorbed into the bloodstream and they have commercial and economic uses, including biological washing powders.
• The ileum is adapted for absorbing digested nutrient molecules due to its large surface area (length, folds and villi), good blood supply, and thin and permeable membranes.
• The structure of a villus is adapted to absorb digested food molecules efficiently due to it having a large surface area - which facilitates absorption, a lacteal leading to the lymph system - which carries away fatty acids, and a thin permeable membrane which allows easy diffusion of molecules into the blood capillaries
• The five stages of digestion are ingestion, digestion, absorption, and egestion
• amylase breaks down carbohydrates, such as starch into glucose. protease breaks down protein into amino acids, lipase breaks down fat into fatty acids and glycerol.