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

Learning outcomes 1)State the roles of water in living organisms 2)List the chemical elements which make up Carbohydrates Fats Proteins 3)Describe and carry out tests for Starch (iodine) Reducing sugars (Benedict’s solution) Protein (Biuret test) Fats (ethanol emulsion) 4)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

Importance of Water 1)Vital constituent of protoplasm (70%) 2)Best solvent for both organic and inorganic substances Prepared by Ms Lam and Mr Alex Lim

Functions of water 1)Medium in which various chemical reactions occur 2)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

Functions of water 3)Essential component of – Digestive juices – Blood – Lubricants in joints 4)Reactant in photosynthetic process in green plants 5)Helps to regulate body temperature when sweat evaporates from skin surface ( maintenance of body temperature at 37°C)

Summary Prepared by Ms Lam and Mr Alex Lim

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 Sources

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

Carbohydrates Organic compound composed of carbon, hydrogen and oxygen in the ratio of 1:2:1 monosaccharides (simple sugars) or disaccharides (complex sugars) Many monosaccharides and disaccharides can be linked together to form polysaccharides E.g. Starch (C 6 H 10 O 5 ) n Generalized form C n H 2n O n Carbohydrates

Functions of Carbohydrates 1)Source of energy 2)Form supporting structures 3)Converted to other organic compounds – Amino acids and fats 4)Formation of nucleic acids – Deoxyribonucleic acid

Test for reducing sugars Benedict’s test – To 2 cm 3 of glucose solution (or sample to be tested) in a test tube, add 2cm 3 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

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.

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

Benedict’s test

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

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

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

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

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

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

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

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

Fats Organic compounds – Carbon, hydrogen, oxygen Unlike carbohydrates Contain much less oxygen in proportion to hydrogen

Functions of fats 1)An efficient source and storage of energy 2)An insulating material to reduce heat loss 3)Constituent for protoplasm 4)Solvent for fat-soluble vitamins (A,D,E,K) 5)Restrict water loss from surface of skin

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.

Structure of fats

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

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

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

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

Ethanol Emulsion test – On liquids To 2cm 3 of an unknown liquid in a test tube, add 2cm 3 of ethanol Shake the mixture thoroughly Add 2cm 3 of water to the mixture and observe for any changes – Negative: Remain clear and colourless – Positive: Form cloudy white suspension

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 2cm 3 of ethanol one drop of sample Emulsion formed. Fat is present.

Ethanol Emulsion test – On solids Cut a solid sample into small pieces To a few pieces of solid sample in a test tube, add 2cm 3 of ethanol Allow the solid particles to settle and decant the ethanol into another test tube containing 2cm 3 of water Observe for any changes to ethanol solution – Negative: Remain clear and colourless – Positive: Form cloudy white suspension Ethanol Emulsion test

Which test tube has an emulsion formed ? Ans: Test tube A. 2 drops of cooking oil 2 cm 3 of alcohol 2 cm 3 of distilled water after shaking to form a clear solution shake and then allow to stand emulsion oil water shake and then allow to stand shaking 2 drops of cooking oil 2 cm 3 of distilled water A B

What happens to the other tube ? Ans: The mixture separates into two layers because fats do not dissolve in water. 2 drops of cooking oil 2 cm 3 of alcohol 2 cm 3 of distilled water after shaking to form a clear solution shake and then allow to stand emulsion oil water shake and then allow to stand shaking 2 drops of cooking oil 2 cm 3 of distilled water A B

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

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

An amino acid molecules

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

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

Test for Proteins Biuret test – To 1 cm 3 of an unknown liquid in a test tube, add 1 cm 3 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

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. 2cm 3 of sodium hydroxide 2cm 3 of protein sample 1% copper sulphate solution added drop by drop Purple solution formed Protein is present

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. copper sulphate solution egg white + sodium hydroxide solution water + sodium hydroxide solution A B

Biuret Test Prepared by Ms Lam and Mr Alex Lim

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

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

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