Enzymes

• The major nutrients required for a healthy diet are carbohydrates, proteins and lipids.
• The digestive system breaks down large molecules of food, which are then absorbed into the bloodstream.
• Carbohydrates are vital for energy in humans and are stored as fat if eaten in excess.
• In plants, carbohydrates are important for photosynthesis.
• Proteins are one of the three main food groups, needed by the body for cell growth and repair.
• Fats or oils, composed of fatty acids and glycerol, must be broken down to be absorbed into the body.
• Enzymes are proteins that have a complex 3D shape and each enzyme has a region called an active site.
• The active site of each enzyme is a different shape, a perfect match to the shape of the substrate molecule, or molecules.
• One enzyme is therefore specific to one substrate's chemical reaction, or type of chemical reaction.
• The lock and key theory compares the specificity of enzymes with a key and its lock.
• Physical factors affect enzyme activity, for example, at low temperatures, the number of successful collisions between the enzyme close enzyme A protein which catalyses or speeds up a chemical reaction

  and substrate close substrate A substance on which enzymes act

  is reduced because their molecular movement close molecular movement The movement of molecules resulting from their kinetic energy

  decreases.
• The human body is maintained at 37°C as this is the temperature at which the enzymes in our body work best.
• Higher temperatures disrupt the shape of the active site, which will reduce its activity, or prevent it from working.
• Enzymes therefore work best at a particular temperature.
• Extreme pH levels can denature enzymes and permanently change their shape.
• For example, pancreatic protease (trypsin) has an optimum pH of 7.5-8.0.
• Enzymes have a unique shape held together by weak forces between the amino acid molecules in the chain.
• Enzymes are proteins made up of amino acid molecules.
• High temperatures can break these forces and change the shape of the enzyme, affecting its activity.
• Amino acids in an enzyme molecule can carry a positive or negative charge, which contributes to the folding of the enzyme and its shape.
• Enzymes are sensitive to pH, and changing the pH can also change the shape of the enzyme and its active site.
• Enzymes have different optimum pH levels, and different parts of the digestive system produce enzymes with different optimum pHs.