Chapter 3

1. Chapter 3 Biological molecules Prepared by Ms Lam and Mr Alex Lim

2. Learning outcomes • State the roles of water in living organisms • List the chemical elements which make up • Carbohydrates • Fats • Proteins • Describe and carry out tests for • Starch (iodine) • Reducing sugars (Benedict’s solution) • Protein (Biuret test) • Fats (ethanol emulsion) • State that large molecules are synthesised from smaller basic units • Glycogen from glucose • Polypeptides and proteins from amino acids • Lipids such as fats from glycerol and fatty acids Prepared by Ms Lam and Mr Alex Lim

3. Importance of Water • Vital constituent of protoplasm (70%) • Best solvent for both organic and inorganic substances Prepared by Ms Lam and Mr Alex Lim

4. Functions of water • Medium in which various chemical reactions occur • Transporting agent • Digested food substances from intestines to other parts of body • Excretory products from tissues to excretory organs • Hormones from glands to regions of body required

5. Functions of water • Essential component of • Digestive juices • Blood • Lubricants in joints • Reactant in photosynthetic • process in green plants • Helps to regulate body temperature when sweat evaporates from skin surface (maintenance of body temperature at 37°C)

6. Summary Prepared by Ms Lam and Mr Alex Lim

7. Sources Water • Can be obtained by drinking it and also by drinking milk, juices and soup • Is lost during urination, perspiration and even breathing • If not replaced, will lead to dehydration, causing muscle cramps and weakness

8. What is biological molecule? Any molecule that is produced by a living organism

9. Carbohydrates Organic compound composed of carbon, hydrogen and oxygen in the ratio of 1:2:1 monosaccharides(simple sugars) or disaccharides (complex sugars) Carbohydrates Many monosaccharides and disaccharides can be linked together to form polysaccharides E.g. Starch (C6H10O5)n Generalized form CnH2nOn

10. Functions of Carbohydrates • Source of energy • Form supporting structures • Converted to other organic compounds • Amino acids and fats • Formation of nucleic acids • Deoxyribonucleic acid

11. Test for reducing sugars • Benedict’s test • To 2 cm3 of glucose solution (or sample to be tested) in a test tube, add 2cm3 of Benedict’s solution • Shake the test tube and immerse it in a beaker of boiling water for 2 minutes • At the end of 2 minutes, observe any change in colour • Negative: Remains blue • Positive: Brick-red precipitate. Sometimes, green, yellow or orange ppt may appear

12. Test for reducing sugars Test for reducing sugars This sugar test is performed by adding a small amount of Benedict’s solution to the sample and bringing the mixture to a boil. If Benedict’s solution remains clear blue, and no precipitate is formed, sugar is absent. The presence of sugar is indicated by the formation of a precipitate from green, through to yellow and orange, to brick red.

13. A B glucose solution + Benedict’s solution distilled water + Benedict’s solution water bath Is there any colour change in tubes A and B ? Ans: Only the mixture in tube A has a colour change.

14. A B glucose solution + Benedict’s solution distilled water + Benedict’s solution water bath What is the sequence of change when there is a colour change ? Ans: The blue solution changes first to green, then to a yellow coloration and eventually a brick-red precipitate is produced.

15. Benedict’s test

16. Glycogen • Storage form of carbohydrate in animals and in fungi • Formed by many glucose molecules • Highly branched chains of glucose units

17. Starch • Storage form of carbohydrate in plants • Form by many glucose molecules • Can be hydrolysed by acid • Bonds broken • Glucose units released

18. Conversion of glucose to starch (in Plants) Why?

19. Conversion of glucose to glycogen (in Human) Why?

20. Iodine test for starch This starch test is performed by adding a few drops iodine solution to the sample. Starch present Starch absent

21. iodine solution distilled water starch solution B A What is the final colour in tube A ? Ans: The solution in tube A changes from brown to blue black.

22. iodine solution distilled water starch solution B A What is the purpose of setting up tube B ? Ans: To act as a control.

23. Cellulose • Main component of cell walls of plants • Inert  only few organisms can digest it • Man cannot digest it • Become bulk of undigested matter • Ease the movement of food and undigested waste along digestive tract

24. Fats • Organic compounds • Carbon, hydrogen, oxygen • Unlike carbohydrates • Contain much less oxygen in proportion to hydrogen

25. Functions of fats • An efficient source and storage of energy • An insulating material to reduce heat loss • Constituent for protoplasm • Solvent for fat-soluble vitamins (A,D,E,K) • Restrict water loss from surface of skin

26. Structure of Fats Fats are compounds that contain carbon, hydrogen and oxygen. A molecule of fat consists of glycerol with chains of fatty acids attached to it. Different kinds of fats have different fatty acids attached to glycerol.

27. Structure of fats

28. Type of fats • Saturated fats • Occurring in animal bodies • Cholesterol found together with saturated fats can get deposited on inside of arteries and lead to heart attacks • Unsaturated fats • Vegetable fats • Do not cause heart diseases • Healthier alternative

29. Fats Oils are fats which are liquid at room temperature. Waxes are fats which are solid at room temperature.

30. Fats • Fats that are solid at room temperature tend to be high in saturated fats. • Saturated fats increase the level of cholesterol in the blood. • Diets rich in cholesterol and saturated fats increases the risk of heart disease. Healthy artery Damaged artery

31. Which substance, oil or water, leaves a permanent translucent spot on the filter paper ? Ans: Oil.

32. Ethanol Emulsion test • Ethanol Emulsion test • On liquids • To 2cm3 of an unknown liquid in a test tube, add 2cm3 of ethanol • Shake the mixture thoroughly • Add 2cm3 of water to the mixture and observe for any changes • Negative: Remain clear and colourless • Positive: Form cloudy white suspension

33. Ethanol emulsion test The presence of fats can be identified with the emulsion test. The test is done by dissolving the sample liquid in ethanol. Water is then added to the mixture. water one drop of sample 2cm3 of ethanol Emulsion formed. Fat is present.

34. Ethanol Emulsion test • Ethanol Emulsion test • On solids • Cut a solid sample into small pieces • To a few pieces of solid sample in a test tube, add 2cm3 of ethanol • Allow the solid particles to settle and decant the ethanol into another test tube containing 2cm3 of water • Observe for any changes to ethanol solution • Negative: Remain clear and colourless • Positive: Form cloudy white suspension

35. 2 drops of cooking oil 2 cm3 of alcohol 2 cm3 of distilled water A after shaking to form a clear solution shake and then allow to stand emulsion 2 drops of cooking oil 2 cm3 of distilled water 2 cm3 of distilled water B oil shaking shake and then allow to stand water Which test tube has an emulsion formed ? Ans: Test tube A.

36. 2 drops of cooking oil 2 cm3 of alcohol 2 cm3 of distilled water A after shaking to form a clear solution shake and then allow to stand emulsion 2 drops of cooking oil 2 cm3 of distilled water 2 cm3 of distilled water B oil shaking shake and then allow to stand water What happens to the other tube ? Ans: The mixture separates into two layers because fats do not dissolve in water.

37. Proteins Proteins are compounds that contain carbon, hydrogen, oxygen and nitrogen.

38. Proteins Proteins are nutrients which are made up of basic units called amino acids. Essential amino acids are necessary to keep the body healthy. There are about 20 different amino acids. 9 of them are essential. different types of amino acids peptide links

39. An amino acid molecules

40. Functions of proteins • Essential for tissue repair • synthesis of cytoplasm, cell membranes and chromosomes • Synthesis of enzymes and some hormones • Formation of antibodies to combat diseases

41. Effects of Protein Deficiency • In children • Lead to a disease called Kwashiorkor • Swollen abdomen • Scaly skin • Permanent growth defects

42. Test for Proteins • Biuret test • To 1 cm3 of an unknown liquid in a test tube, add 1 cm3 of sodium hydroxide solution • Shake thoroughly • Add 1% copper(II) sulphate solution, drop by drop into the mixture, shaking after every drop • Observe for any colour change • Turn Violet: Proteins are present • Turn Pink: Peptones are present • Remain Blue: Proteins are absent

43. Biuret test The presence of proteins can be identified with the Biuret test. The test is done by dissolving the sample liquid in ethanol. Water is then added to the mixture. 2cm3 of sodium hydroxide 1% copper sulphate solution added drop by drop 2cm3 of protein sample Purple solution formed Protein is present

44. copper sulphate solution egg white + sodium hydroxide solution water + sodium hydroxide solution B A What colour changes in tubes A and B ? Ans: Mixture in tube A changes from blue to purple while mixture in tube B remains blue without any change.

45. Biuret Test Prepared by Ms Lam and Mr Alex Lim

46. Balanced Diet • have enough food to supply enough • energy • carbohydrates, fats, proteins • body building materials • proteins • substances to maintain health • vitamins, minerals, water & dietary fibres • malnutrition :not having balanced diets for long time

47. Factors affecting energy requirement • Sex • Age • Occupation • Physical Activities • Stage of individual(pregnancy, breast-feeding)

48. GOOD LUCK FOR EXAMINATIONS!!!!! (don’t depend too much on luck though… work smart and hard too!)