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  2. ENZYMES • Enzymes are proteins • They are biological catalysts • Catalysts are substances which speed up the rate of a chemical rxn without being used up. Hence they will be available for other rxns.

  3. Human saliva contains an enzyme called amylase. This enzyme helps to turn starch into a sugar called maltose. • When you swallow a mouthful of food, the amylase stops working because it is much too acid in the stomach (pH 2). • Amylase works best in neutral or slightly alkaline conditions, i.e. at about pH 7. • When your food gets into the small intestine, more amylase is made by the pancreas and this turns the remaining starch into maltose. • Another enzyme (maltase) turns all this maltose into glucose. Glucose is then absorbed into the blood.

  4. TYPES OF ENZYMES amylase

  5. Digestive enzymes are enzymes that break down food into usable material. The major different types of digestive enzymes are: • Amylase – breaks down carbohydrates, starches, and sugars which are prevalent in potatoes, fruits, vegetables, and many snack foods • lactase – breaks down lactose (milk sugars) • sucrase – digests complex sugars and starches • maltase – digests disaccharides to monosaccharides (malt sugars)

  6. Protease – breaks down proteins found in meats, nuts, eggs, and cheese • pepsin – breaks down proteins into peptides • peptidase – breaks down small peptide proteins to amino acids • trypsin – derived from animal pancreas, breaks down proteins • Lipase – breaks down fats found in most dairy products, nuts, oils, and meat

  7. Some enzymes that digest food in the gut(substances in bold are end products that can be absorbed into the blood)

  8. HOW ENZYMES WORK • Enzymes have an active site. This is part of the molecule that has just the right shape and functional groups to bind to one of the reacting molecules. • The reacting molecule that binds to the enzyme is called the substrate. • An enzyme-catalysed reaction takes a different 'route'. The enzyme and substrate form a reaction intermediate. • Its formation has a lower activation energy than the reaction between reactants without a catalyst.

  9. A simplified equation: • Route A: reactant 1 + reactant 2   product     • Route B: reactant 1 + enzyme     intermediate   intermediate + reactant 2     product + enzyme • So the enzyme is used to form a reaction intermediate, but when this reacts with another reactant the enzyme reforms.

  10. Animation: •

  11. energy Reaction profiles: uncatalysed and enzyme-catalysed Uncatalysed reaction Enzyme-catalysed reaction Intermediate – formed between enzyme and one or more reactant molecules reactants exergonic reaction products Course of reaction

  12. energy no enzyme present enzyme present Intermediate : enzyme/reactant 1 + reactant 2 reactant 1 + reactant 2 + enzyme products + enzyme Course of reaction

  13. FACTORS AFFECTING ENZYME ACTIVITY TEMPERATURE • As the temperature rises, reacting molecules of substrate & enzyme have more and more kinetic energy. This increases the chances of a successful collision and so the rate increases. • There is a certain temperature at which an enzyme's catalytic activity is at its greatest. This optimal temperature is usually around human body temperature (37.5 oC) for the enzymes in human cells. • Above this temperature (usually over 40oC)the enzyme structure begins to break down/lose their shape (denature) since at higher temperatures intra- and intermolecular bonds are broken as the enzyme molecules gain even more kinetic energy.

  14. This can be seen when an egg is boiled. • Egg white is protein, & turns from a clear runny liquid into a white solid as the heat denatures the protein. • NB: Some bacteria may have an optimum temperature of 10 oC or 75 oC (those in hot springs) • Enzymes from plants have optimum temperatures around 28 – 30 oC

  15. Graph showing the Effect of temperature on enzyme activity

  16. pH • Each enzyme works within quite a small pH range. There is a pH at which its activity is greatest (the optimal pH). • Most human enzymes are their correct shape ~ pH of 7 • This is because changes in pH can make and break intra- and intermolecular bonds, changing the shape of the enzyme thus the active site can no longer fit the substrate and, therefore, its effectiveness.

  17. Pepsin has an optimum pH of 2 since it works best in acidic conditions of the stomach.

  18. SUBSTRATE CONCENTRATION • The rate of an enzyme-catalysed reaction depends on the concentrations of enzyme and substrate. As the concentration of either is increased the rate of reaction increases (see graphs). • For a given enzyme concentration, the rate of reaction increases with increasing substrate concentration up to a point, above which any further increase in substrate concentration produces no significant change in reaction rate.

  19. This is because the active sites of the enzyme molecules at any given moment are virtually saturated with substrate. The enzyme/substrate complex has to dissociate before the active sites are free to accommodate more substrate. (See graph) • Provided that the substrate concentration is high and that temperature and pH are kept constant, the rate of reaction is proportional to the enzyme concentration. (See graph)

  20. DIET • Animals are heterotrophic i.e. they depend on other organisms for food. • Term dietrefers to food an animal eats daily. • What is a balanced diet? • One that contains carbohydrates, lipids, proteins, vitamins, mineral salts, fibre/roughage and water in the correct amounts and proportions.

  21. VITAMINS & MINERALS • Vitamins – organic substances which help control metabolism • A few are produced by our bodies whereas the rest come from the food we eat. • Some (like Vitamin K) are produced by bacteria in our intestines. Vitamin K helps blood to clot. • Some minerals are important for growth & repair of our bodies, others control metabolism.

  22. We need small amounts of minerals from our food for good health. • Calcium is an important mineral. It is needed for strong bones & teeth & for blood to clot. • An adult needs about 1.1g of Ca a day. • An adult needs 16mg of iron a day. • See tables on pages 64 & 66 – Atwaroo and pages 72 & 73 in Chinnery • (NB Vitamins are organic substances made by plants & animals while minerals are inorganic elements that come from soil & water & are absorbed by plants & animals e.g. calcium)

  23. WATER • Our body has about ⅔ (~70%) water. • Why is it important? • It is important for chemical rxns (solvent). • It is the solvent in which waste matter is transported & passed out of the body in solution. • Water in blood and lymph fluids is used to transport materials around our bodies. • It keeps the body cool.

  24. We need ~2 ½ litres of water daily. • If we don’t get enough water we become dehydrated and cellular processes can’t occur. • How do we gain & lose water? • We can only survive a few days w/o water.

  25. FIBRE • What is the source of fibre? • Fibre in our diets come from plants. • Soluble fibre dissolves in water • Insoluble fibre does not dissolve but holds water & swells up with water. • Soluble fibre comes from fruit pulp, vegetables, oat bran & dried beans • Insoluble water comes from cellulose of plant cell walls & husks that cover wheat, rice & other grains.

  26. Insoluble fibre adds to the bulk of undigested food passing through intestines & maintains peristalsis by giving muscles something to push against. • Fibre can also reduce the amount of fat absorbed from food & this in turn reduces the risk of bowel cancers. • A lack of fibre causes constipation which can lead to bowel cancer in the long term.


  28. How much food do we need in a balanced diet? • Every day, a person uses energy (E). • The amount used depends on age, gender, where you live and activities done. • Food supplies us with energy. • The amount of E in food is measured in kilojoules (kJ). • Men need more E than women. • Kids & young adults need a lot of E. Why?

  29. People who exercise or are active need more than those with sedentary lifestyles. • People who live in cold climates burn more E and thus eat more than those in warmer climates. Why? • See charts on page 67 Atwaroo and pages 70 & 71 (Table 5.1) in Chinnery

  30. The 5 food groups & recommended daily intake of each

  31. The average daily energy requirements are 2000 kcal for women and 2500 kcal for men

  32. Effects of an unbalanced diet • Malnutrition means bad nourishment. • It results from an unbalanced & unhealthy diet. • Who are malnourished? What does it mean? • When don’t get enough food, or not getting enough variety of food or eating too much food.

  33. Gout is a condition characterized by an abnormal metabolism of uric acid. People with gout either produce too much uric acid, or more commonly, their bodies have a problem in removing it.

  34. Vegetarian diets • Eat mainly foods from plants. • This diet is chosen for many reasons: against cruelty to animals, religion, think it is healthier. • Must ensure that they have a balanced diet. Why? • This diet has more fibre, less saturated fat & cholesterol & less high-energy food. • Less likely to be overweight • Have lower risk of heart disease, diabetes and some types of cancers

  35. Vegans don’t eat any food derived from animals including honey. • Special care should be taken if children are being brought up on a vegetarian diet. Why? • Parents must ensure that the child has a wide range of foods in the diet with plenty of protein, minerals and vitamins.

  36. DIGESTION • Absorption – small molecules are absorbed into the blood. • Digestion – break down of large molecules into smaller ones • Ingestion – food is taken into the alimentary canal • Egestion – food could not be digested or absorbed is removed from the body.

  37. Mechanical vs. chemical digestion • Mechanical – large pieces are broken up by teeth into smaller bits and by churning of alimentary canal. • Chemical – once the food is broken up, the large molecules are further broken up into small ones i.e. there is a chemical change from one molecule to the next. Enzymes are involved in this process.

  38. ROLE OF TEETH • Read sections on teeth in Atwaroo and Chinnery. • Learn different types of teeth & their functions. • Draw diagram of tooth and annotate parts of teeth. • Summarise role of teeth in notebook. • Learn importance of dental hygiene.

  39. THE DIGESTIVE SYSTEM • Name the parts of the digestive system. • Do you know what they do? • Where does digestion begin? • Where does it end?

  40. THE DIGESTIVE SYSTEM • The alimentary canal is a long muscular tube which runs from the mouth to the anus. • This along with the liver and pancreas makes up the digestive system. • The wall of the alimentary canal contains muscles which contract & relax to make food move along. • This movement along the canal – peristalsis.

  41. The alimentary canal contains special muscles which hold food in one part of the canal until it is ready to move to another part of the canal. These muscles are called sphincter muscles. • Movement along the canal is aided by the secretion of mucus which are made by goblet cells.

  42. IN THE MOUTH • Digestion begins in the mouth • After the food is broken up by the teeth, the food is mixed with saliva & formed into a bolus/ball. • The saliva contains water, mucus & amylase enzyme. • The water dissolved the food allowing us to taste it. • The mucus binds the chewed food together & helps it to slide easily down the oesophagus

  43. Amylase begins to digest starch to maltose. Hence, this is the first area for carbohydrate digestion. • The tongue helps roll the bolus which exits the mouth into the oesophagus via swallowing.

  44. Draw diagram of digestive system and annotate parts. • IMPORTANT: Take note of any enzymes in each organ and their functions in your annotations. • Note functions of liver in both books (pg 78 & 79 Atwaroo & 83, 148, 149 in Chinnery) and write summary in notebook.