Enzymes & Digestion

• Enzymes

  Catalysts: substances that speed up chemical reactions. The enzyme molecules are temporarily changed during their action and can be used over and over again. So, even a small amount of enzyme is enough

  
• Enzymes


  • Proteins in nature
  • Specific in their action (one enzyme speeds up one reaction only)
  • Temperature sensitive (above 40oC enzymes are denatured, cooling slows down their action and they become inactivated)
  • pH sensitive (each enzyme has its own preferred pH range)
  • Require water to function
  • Produced by living cells

  
• Without enzymes, reactions would not go fast enough for life to exist
• Substrate


  The substance on which the enzyme acts
• Rate of reaction


  Increases with temperature
• Active site


  Enzymes have a 3-D shape with an active site that allows the reactant/substrate molecules to fit in snugly (lock and key mechanism). This is what makes the enzyme specific to one reactant/substrate
• At the end of the reaction the products leave the active site and the enzyme remains unchanged and ready to do the same to another reactant/substrate molecule
• Economic importance of enzymes

  • Used in biological washing powders to break down proteins and fats
  • Used in the food industry to extract fruit juices and break down proteins in baby food
• Human digestion


  1. Physical digestion by chewing in the mouth

  2. Chemical digestion by salivary amylase in the mouth

  3. Swallowing

  4. Peristalsis in the esophagus

  5. Acid production and pepsin enzyme in the stomach

  6. Pancreatic enzymes, bile, and intestinal enzymes in the small intestine

  7. Absorption in the small intestine

  8. Water absorption and storage of undigested matter in the large intestine

  
• Villi


  • Large surface area for absorption
  • Rich blood supply
  • Moist with digestive juices
  • Thin one-cell thick wall
• Absorption of digestive products

  1. Diffusion and active transport across the lining of the villi

  2. Fatty acids and glycerol recombine and enter the lacteals in the villi

  3. Other products enter the capillaries which join to form the hepatic portal vein that carries blood to the liver

  
• Assimilation is the incorporation of absorbed food into various parts of the body
• Large intestine


  • Mainly composed of the colon and rectum
  • Absorbs water from undigested matter
  • Stores faeces composed of indigestible food, bacteria, and dead cells

  
• In herbivores, the caecum and appendix contain bacteria that digest cellulose
• Summary of enzymes and digestive juices

  • Salivary amylase (mouth)
  • Pepsin (stomach)
  • Bile salts (duodenum)
  • Trypsin, pancreatic amylase, lipase (duodenum)
  • Maltase, peptidases, sucrase (duodenum wall)
• The liver


  • Largest organ in the body with over 500 functions
  • Stores and releases glycogen
  • Forms urea from excess amino acids
  • Desaturates fats
  • Stores vitamin B12 and iron
  • Produces heat
• Glycogen conversion to glucose


  Glycogen is converted to glucose under the control of glucagon, a hormone produced by the pancreas
• Formation of urea


  1. Amino acids are taken to the liver in the hepatic portal vein

  2. Nitrogen-containing part of the amino-acids is removed and changed to urea

  3. This process is known as deamination
• Desaturation of fats


  1. Fats are stored in the body in a saturated form

  2. Before saturated fats can be used by the tissues of the body they must be unsaturated and this occurs in the liver

  3. The resulting unsaturated fats can provide energy for the body
• Liver functions


  • Storage of vitamin B12
  • Storage of iron
  • Production of heat
  • Production of blood clotting agents
  • Makes poisons harmless eg alcohol
• Hepatic artery


  Brings oxygenated blood from the aorta
• Hepatic portal vein


  Brings absorbed food from the alimentary canal
• Hepatic vein


  All blood leaving the liver travels along it to the vena cava

  
• Destination of end-products of digestion

  • Glucose
  • Amino acids
  • Fats, fatty acids and glycerol
• Ingestion

  The intake of food through the mouth
• Digestion


  The breakdown of food both physically and chemically into smaller pieces
• Absorption


  Small, soluble products are absorbed through the membranes of the gut cells
• Assimilation


  Absorbed food is used or stored in the body
• Excretion


  Removal of waste products from digestion from the normal body circulation (still retained in the body)
• Egestion


  Indigestible food is eliminated through the anus
• Digestion is the breakdown of food both physically and chemically into smaller pieces
• Chemical digestion is the breakdown of food using enzymes
• Two functions of the epithelium are
• Peristalsis


  The process by which the gut muscles force food along the intestine in one direction
• Sphincter muscles


  • Found in the mouth
  • Found in the anus
• Salivary amylase


  Enzyme found in the mouth, made in the salivary glands
• Functions of saliva


  • Lubricates food
  • Contains enzymes to start digestion
• Swallowing food


  Food is moved from the mouth to the stomach by muscular contractions

  
• Stomach

  A J-shaped bag-like organ
• Chyme


  The semi-digested food mixture in the stomach