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Biological molecules

Biological molecules. Learning objective: To consolidate learning of biological molecules. Which molecule, A to E, (a) is one of the monomers which combine to form starch; D (b) contains peptide bonds; A (c) could be an oil; B (d) is one of the molecules that form a triglyceride? E.

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Biological molecules

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  1. Biological molecules Learning objective: To consolidate learning of biological molecules

  2. Which molecule, A to E, (a) is one of the monomers which combine to form starch; • D (b) contains peptide bonds; • A (c) could be an oil; • B (d) is one of the molecules that form a triglyceride? • E • What is the remaining molecule? • An amino acid

  3. Carbohydrates • Grasses store carbohydrate as fructans, which are polymers of a monosaccharide called fructose. • The diagram shows the structural formula of each of two fructose molecules. • (a) (i) Draw a box round the parts of the two fructose molecules that would be removed when the two molecules are joined together. (1 mark)

  4. (ii) Name the process in which monosaccharides join together. • Condensation • (iii) How many carbon atoms does a molecule of fructose contain? • 6 (b) The table shows the percentage of carbohydrates in the dry mass of a sample of young grass. • (i) The sample of young grass contains 80% water. Calculate the mass of cellulose in 1 kg of this grass. Show your working. • 25% of 20% of total mass= 5% • 5% of 1kg = 50g • 50 gains 2 marks. • 25% × 200, or equivalent, gains 1 mark.

  5. (ii) Cellulose is a constituent of the cell walls of the grass. • Explain how the structure of cellulose molecules gives strength to the cell walls • Long straight chain (of glucose molecules) / 1-4 link in context; • Hydrogen bonds hold molecules together; • able to form (micro)fibrils. • (c) Cows feed on grass, but they do not produce enzymes that can digest cellulose or some of the fructans. The rumen is large and contains microorganisms which secrete enzymes that can break down cellulose and fructans. Use information from the table in part (b) to explain the advantage to cows of having such microorganisms in their rumen. • High proportion/'lots'of carbohydrate unused if cellulose/fructans • not digested / 'lots' of energy wasted. • (not just: 'grass has a lot of cellulose & fructans')

  6. Lipids In humans, triglycerides are stored under the skin in the cells of the adipose layer. Triglycerides are compounds of glycerol and fatty acids. • Explain why the adipose layer is described as a ‘tissue’. • Cells all the same/similar structure/function.

  7. (b) The structural formula of glycerol is: The structural formula of a fatty acid is: R – COOH. (i) In the space below, draw the structural formula of a triglyceride.

  8. (ii) Name the process in which fatty acids are combined with glycerol. • Condensation / esterification. (c) (i) Describe the effect on melting point of including unsaturated fatty acids in a triglyceride. Unsaturated fatty acids/ lower the melting point. (ii) Analysis of the triglycerides in adipose tissue shows that about 50% of the fatty acids are unsaturated. Suggest the advantage of this. • Triglycerides are oils / melting point below body temperature; • Explanation of advantage, • e.g. prevents hard layer of fat forming under skin / mobility of lipid / deposition in arteries. (d) Triglycerides are broken down in the digestive system. (i) Name the enzyme that digests triglycerides. • Lipase. (ii) Name one organ which produces this enzyme. • Pancreas/salivary glands/small intestine

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