Topic 9.7

1. Digestion-Part One Topic 9.7

2. Contents Digestion – Part One Energy from food The digestive system Teeth Enzyme properties Digestive enzymes Summary

3. minerals fats water fibre vitamins carbohydrates proteins Energy from food: The 7 food groups represent large chemicals. These chemicals are often chains of smaller, more useful chemicals, joined together.

4. One example is carbohydrates. Carbohydrates are made of long chains of identical small sugar molecules. sugar molecule carbohydrate Energy molecules in food

5. ENERGY Small sugar molecules The small sugar molecules are very useful. The body has to break these large food molecules up into single or small chain sugar molecules. These are used to make…

6. How can we release energy from food? Problem One - releasing smaller sugars Physical means like slicing and cleaving food does not break down the long chain molecules and release the sugars. This is because we can’t release sugars from carbohydrates by physically breaking them up.

7. The chain of sugars is held together by… chemical bonds Chemical bonds require a chemical technique if they are to be broken. Chemical breakdown

8. Problem with food size Problem 2 - The food we start with is often large in size. Being large, the food tends to be unable to dissolve. We say it is large and insoluble.

9. The food needs to be soluble so that it can dissolve in the blood and thus, be transported around the body. The smaller the food, the more likely they will dissolve. So the digestive system has to cope with both these problems. Soluble product Digestion Blood vessel Food solubility

10. Contents Digestion – Part One Energy from food The digestive system Teeth Enzyme properties Digestive enzymes Summary

11. The digestive system: The digestive system, being an organ system, is made of a group of organs all working together. Each organ has a particular function and only by working together will they get the job done.

12. Mouth Anus What happens to the food in our bodies? External digestive system The only visible parts of the digestive system are the entry and exit points. The sound of a rumbling stomach and the fact that food looks very different when it leaves, compared to when it enters mean that the body must be doing something to the food during its journey.

13. What happens to the food in our body? It is digested. This means it is broken down. This digestion happens in 2 ways. As we know all food has a physicalshape and is made of chemicals. These chemicals are held together by chemical bonds.

14. physical chemical Chemical and physical digestion • Our digestive system uses both: • chemical digestion • physical digestion • As we move through the digestive system, we will see one or both of these methods in action at any one time. The shape of the food must be physically changed so that it can fit through the small diameter of the digestive system. This allows useful chemicals to be released and dissolve in the blood. To be broken down chemically, the bonds must be broken.

15. Open wide In we go! Digestion is the chemical and physical breakdown of large insoluble molecules into small soluble molecules. Let’s take a close look at how this happens…

16. The digestive tract All food enters our digestive system through the mouth and waste material leaves through the anus. The digestive system is really one long tube with an opening at each end. Stretched out it is a 9m tube! mouth anus

17. But how does a 9m tube fit into a space, which is less than a metre long? Our guts It is extremely folded! In addition, the tube passes through organs on its route from the mouth to the anus.

18. Digestive system diagram

19. Physical digestion The mouth is where digestion begins. Here we find both chemical and physical methods of digestion. We will consider physical digestion first. If you look in the mirror and smile, you immediately notice your teeth. You will also realise that your teeth are different shapes. You have 4 basic types of teeth; each type is designed for a different role.

20. Contents Digestion – Part One Energy from food The digestive system Teeth Enzyme properties Digestive enzymes Summary

21. central incisor latent incisor canine 1st premolar 2nd premolar 1st molar 2nd molar 3rd molar Teeth: Each is designed to do a different job. premolar molar canine incisor

22. Diagram of a tooth

23. Tooth size and shape The shape and size of each tooth is related to the function they have in digesting food. If we look at the teeth of other animals many of them too have these 4 types of teeth. However, the number of each type, their size and their shape differ between species. This is because other organisms have different diets.

24. Canine Sharp pointed teeth, which are used to bite and tear food. Incisors Small rectangular shaped teeth, which are found between the canines. They are used for cutting food. Premolars Found behind the canines and are used to grind soft food. Molars Found behind the premolars and are used to grind hard food. Mammalian tooth types

25. Action in the mouth Together, these teeth can break up most foods that we put into our mouths. The mechanical act of chewing food is part of physical digestion. Once the teeth have digested the food, it may be small enough to be swallowed. However, some food can be sharp and it would be uncomfortable to swallow. The food also needs chemically breaking down. Therefore, the mouth produces a substance that solves both of these problems at the same time.

26. Saliva These glands (a special type of tissue) produce saliva, a sticky liquid. • As mentioned, the saliva has two jobs. • Being a liquid, it softens the food and allows the digested food to be rolled into a ball just before it is swallowed. • It also contains a chemical known as an enzyme.

27. Contents Digestion – Part One Energy from food The digestive system Teeth Enzyme properties Digestive enzymes Summary

28. Enzyme properties: What is an enzyme? Enzymes are chemicals, which act to speed up chemical reactions. They are produced from glandular tissue, which is found all over the body. In order to understand how an enzyme works, you have to think of it as having a particular shape. Somewhere on the surface of the enzyme is an important region known as the active site.

29. We will use the shape below to represent on particular enzyme. Active site enzyme In order for an enzyme to be able to speed up or catalyse a reaction, it must attach to the chemicals that are reacting. It does so using its active site. What’s so special about enzymes?

30. The red areas on these two reacting chemicals represents the areas where the active site of the enzyme will attach. The enzyme will attach to both at the same time. + Specificity of enzymes Enzymes are very specific. Enzymes can only speed up certain reactions. If the shape of the reacting chemicals does not match the shape of the active site, the enzyme will not be able to work.

31. You probably have a certain place to work, or you work at a certain time, you may like listening to music whilst you work or else you can only work if it is completely silent. The environment matters Therefore, enzymes are specific to certain reactions. Enzymes are also very particular about the environment that they work in. To understand this, think of how you do homework.

32. Different enzymes work best in different conditions. If the condition is wrong, their active site can change shape. Say one particular enzyme works best in acidic conditions (pH less than 7). If the pH rises and the conditions become alkaline, the enzyme changes shape and stops working. It can no longer fit with the reacting particles of the chemical reaction. pH< 7 pH 10 Enzymes and pH

33. Food groups and enzymes The bulk of the food that enters the digestive system is from the three main food groups: proteins carbohydrates fats Therefore, it is not surprising that the digestive system has enzyme-producing glands that relate to these three types of food. Remember that the shape of the chemicals within the different food groups will be different. Therefore the shape of the enzymes that digest these chemicals will also be different.

34. Contents Digestion – Part One Energy from food The digestive system Teeth Enzyme properties Digestive enzymes Summary

35. sites of enzyme attack sugar Digestive enzymes: Carbohydrates are chains of identical sugar molecules. The enzyme that digests carbohydrates must be able to break the chemical bonds between the individual sugar molecules. The product of the chemical breakdown of carbohydrates is sugar. The sugar is known as glucose. Enzymes that digests carbohydrates are known as carbohydrases.

36. Enzyme driven reaction The digestion of carbohydrates can be represented by the following equation. carbohydrase Carbohydrates Sugars carbohydrase

37. Imagine a bead necklace made up of over 20 different kinds of bead. sites of enzyme attack amino acids Proteins and amino acids As with carbohydrates, proteins are made of chains of chemicals. However, instead of the chain containing identical molecules, in protein these molecules are different. Protein is made up of chains of amino acids. There are over 20 different kinds of amino acid.

38. The enzymes that digest proteins must be able to break the chemical bonds between the different amino acids. Enzymes that digest protein are known as sites of enzyme attack amino acids proteases. The digestion of proteins can be represented by the following equation. protease Protein Amino Acids Enzymes for digesting proteins

39. Fats are made up of a molecule of glycerol phosphate attached to three fatty acid molecules. The enzymes that digest fats must be able to break the chemical bonds between the glycerol phosphates and the fatty acids. Fats are also known as lipids. fatty acids site of enzyme attack glycerol phosphate Fat in our food

40. Fat digestion can be represented by the following equation: lipase Fat Fatty Acids + Glycerol Phosphate Enzymes for digesting fat The enzymes that digest fats must be able to break the chemical bonds between the glycerol phosphates and the fatty acids. Fats are also known as lipids. Enzymes that digest fat (lipid) are known as lipases.

41. Carbohydrase in saliva Of these three enzymes, the only one that is released within the mouth is carbohydrase. This is partly because the conditions within the mouth are suitable for carbohydrase action. It works best within an alkaline (pH > 7) environment. The carbohydrase in saliva in combination with other digestive carbohydrases added later from the pancreas and the small intestine complete carbohydrate digestion.

42. Digestive action of the mouth - summary Carbohydrates Fats Proteins physical digestion chemical digestion The food could now pass down either the trachea (windpipe) or the gullet/oesophagus. chemically and physically digested physically digested sugars

43. Contents Digestion – Part One Energy from food The digestive system Teeth Enzyme properties Digestive enzymes Summary

44. Multiple-choice quiz