1.4 enzymes and digestion

• A protein molecule is made of a long chain of amino acids
• The long chains of amino acids gets folded to produce a new protein to give it a unique shape
• Proteins produce hormones, enzymes, antibodies and structural tissues and muscles
• In living organisms, chemical reactions which take place are called metabolic reactions
• To make a chemical reaction more susceptible to occur, we can stir or shake the mixture, heating the mixture or using a catalyst
• A catalyst is a substance which changes the rate of chemical reactions (by usually speeding them up)
• An enzyme is a biological catalyst made of proteins, they speed up metabolic reactions
• Enzymes are involved in speeding up reactions, breaking down reactions and changing one molecule into another.
• One region is called the active site, where the substrate slots into the enzyme
• The lock and key theory is a model of enzyme action that describes how the active site of an enzyme fits the substrate
• The substrate and the active site have a complimentary shape. The substrate fits into the active site like and 'key and lock'
• Once the product has been released from the active site, the enzyme can be used again
• When there is excess substrate in a reaction with a high enzyme concentration, the rate of an enzyme controlled reaction increases as more active sites become available. However, when the the concentration of substrate is limited, an increase in enzyme concentration no longer has any effect. So, the rate of reaction no longer increases, therefore it plateaus.
• In a mixture, the enzyme and substrate molecules will be moving around randomly. When they both collide, a reaction can occur. The warmer the solution, the more collisions can form since the kinetic energy builds up. Therefore, the rate of the reaction increases.
• The optimum temperature range for most enzymes is between 30-50 degrees Celsius. This is because at higher temperatures, the bonds holding the tertiary structure together start to break down. At lower temperatures, the enzyme becomes less flexible so the substrates cannot fit into the active site.
• The denaturation of enzymes is the process by which the shape of its active site is changed.
• The optimum temperature/pH/enzyme concentration is the point where the enzyme works at its fastest rate.
• When the value of temperature/pH is adjusted slightly in an enzyme's environment, this can affect the rate of reaction or can denature an enzyme.
• Thermostable means an enzyme which can withstand high temperatures without being denatured.
• Biological washing powders use enzymes to remove stains efficiently as enzymes can break down large insoluble BIOLOGICAL stains (such as sweat, grass, food) into small soluble molecules so they can be washed out easily. This can save electricity too as the enzymes do not need high temperatures to work at.
• Digestions means breaking down large, insoluble molecules into small soluble molecules so they can be absorbed into the blood easier.
• Amylase is an enzyme which is found in the mouth and pancreas and it breaks down starch molecules into small glucose molecules.
• Lipase is an enzyme which is found in the pancreas and it breaks down lipid molecules into fatty acids and glycerol.
• Protease is an enzyme which is found in the stomach and pancreas and it breaks down protein molecules into amino acids.
• The digestive system's organs are the mouth (buccal cavity), salivary glands, oesophagus, stomach, pancreas, liver, gallbladder, small intestine, large intestine, rectum, anus and appendix.
• The small intestine consists of the duodenum (30cm) and ileum (4-5m)
• Ingestion means to put food into the mouth
• Physical digestion consists of mechanical chewing using the teeth. Chemical digestion is the secretion of salivary amylase to start the breaking down of starch to sugars
• Peristalsis is known as the wave like contractions of the stomach and oesophagus.
• Gastric juice consists of hydrochloric acid (to kill bacteria) and protease (to break down proteins)
• Bile is produced in the liver and it neutralises stomach acids (since bile is alkaline) and it helps to emulsify fats
• Emulsification is the process of breaking down fats into smaller droplets.
• Pancreatic juice is made up of amylase, protease and lipase
• Egestion means the removal of faeces from the body through the anus.
• The ileum is adapted for food absorption because of its thin walls, large surface area, rich blood supply, and folded wall
• Villi are finger-like folds in the ileum to increase its surface area. Microvilli are additional folds on the villi to increase the surface area furthur.
• A villus is adapted to its function by a lacteal, which is a lymph vessel which transports fatty acids and glycerol into the blood. Each villus contains a extensive capillary network , which sugars and amino acids are directly absorbed into the blood. Finally, each villus lining is one cell thick, which provides a higher rate of absorption.
• Sugars, amino acids, vitamins and mineral ions are carried away from the blood to the liver for initial processing.
• The fatty acids and glycerol (digested lipids) are carried in the lymphatic system and then through to the circulatory system.