Biological moleculesBiological molecules

Learning objective:Learning objective:

•To consolidate learning of To consolidate learning of biological moleculesbiological molecules

Which molecule, A to E,Which molecule, A to E,(a) is one of the (a) is one of the

monomers which monomers which combine to form combine to form starch; starch;

• DD

(b) contains peptide (b) contains peptide bonds; bonds;

• AA

(c) could be an oil; (c) could be an oil; • BB

(d) is one of the (d) is one of the molecules that form a molecules that form a triglyceride? triglyceride?

• EE

What is the What is the remaining remaining molecule?molecule?

•An amino acidAn amino acid

Carbohydrates• Grasses store carbohydrate as fructans, which are polymers Grasses store carbohydrate as fructans, which are polymers

of a monosaccharide called fructose.of a monosaccharide called fructose.• The diagram shows the structural formula of each of two The diagram shows the structural formula of each of two

fructose molecules.fructose molecules.

• (a) (i) Draw a box round the parts of the two fructose (a) (i) Draw a box round the parts of the two fructose molecules that would be removed when the two molecules molecules that would be removed when the two molecules are joined together. are joined together. (1 mark)(1 mark)

• (ii) Name the process in which monosaccharides join (ii) Name the process in which monosaccharides join together.together.

• CondensationCondensation • (iii) How many carbon atoms does a molecule of (iii) How many carbon atoms does a molecule of

fructose contain?fructose contain?• 66(b) The table shows the percentage of carbohydrates in (b) The table shows the percentage of carbohydrates in

the dry mass of a sample of young grass.the dry mass of a sample of young grass.• (i) The sample of young grass contains 80% water. (i) The sample of young grass contains 80% water.

Calculate the mass of cellulose in 1 kg of this grass. Calculate the mass of cellulose in 1 kg of this grass. Show your working.Show your working.– 25% of 20% of total mass= 5%25% of 20% of total mass= 5%– 5% of 1kg = 50g5% of 1kg = 50g– 50 gains 2 marks.50 gains 2 marks.– 25% × 200, or equivalent, gains 1 mark.25% × 200, or equivalent, gains 1 mark.

• (ii) Cellulose is a constituent of the cell walls of the grass.(ii) Cellulose is a constituent of the cell walls of the grass.• Explain how the structure of cellulose molecules gives Explain how the structure of cellulose molecules gives

strength to the cell walls strength to the cell walls • Long straight chain (of glucose molecules) / 1-4 link in Long straight chain (of glucose molecules) / 1-4 link in

context;context;• Hydrogen bonds hold molecules together;Hydrogen bonds hold molecules together;• able to form (micro)fibrils.able to form (micro)fibrils.• (c) Cows feed on grass, but they do not produce enzymes (c) Cows feed on grass, but they do not produce enzymes

that can digest cellulose or some of the fructans. The that can digest cellulose or some of the fructans. The rumen is large and contains microorganisms which rumen is large and contains microorganisms which secrete enzymes that can break down cellulose and secrete enzymes that can break down cellulose and fructans. Use information from the table in part (b) to fructans. Use information from the table in part (b) to explain the advantage to cows of having such explain the advantage to cows of having such microorganisms in their rumen.microorganisms in their rumen.

• High proportion/'lots'of carbohydrate unused if High proportion/'lots'of carbohydrate unused if cellulose/fructanscellulose/fructans

• not digested / 'lots' of energy wasted.not digested / 'lots' of energy wasted.• (not just: 'grass has a lot of cellulose & fructans')(not just: 'grass has a lot of cellulose & fructans')

Lipids

In humans, triglycerides are stored under the skin in In humans, triglycerides are stored under the skin in the cells of the adipose layer.the cells of the adipose layer.

Triglycerides are compounds of glycerol and fatty Triglycerides are compounds of glycerol and fatty acids.acids.

(a)(a) Explain why the adipose layer is described as a Explain why the adipose layer is described as a ‘tissue’.‘tissue’.

• Cells all the same/similar structure/function.Cells all the same/similar structure/function.

(b) The structural formula of glycerol is: (b) The structural formula of glycerol is:

The structural formula of a fatty acid is: The structural formula of a fatty acid is:

R – COOH.R – COOH.

(i) In the space below, draw the structural formula of a (i) In the space below, draw the structural formula of a triglyceride.triglyceride.

(ii) Name the process in which fatty acids are combined with (ii) Name the process in which fatty acids are combined with glycerol.glycerol.

• Condensation / esterificationCondensation / esterification..(c) (i) Describe the effect on melting point of including (c) (i) Describe the effect on melting point of including

unsaturated fatty acids in a triglyceride.unsaturated fatty acids in a triglyceride.Unsaturated fatty acids/ lower the melting pointUnsaturated fatty acids/ lower the melting point..(ii) Analysis of the triglycerides in adipose tissue shows that (ii) Analysis of the triglycerides in adipose tissue shows that

about 50% of the fatty acids are unsaturated. Suggest the about 50% of the fatty acids are unsaturated. Suggest the advantage of this.advantage of this.

• Triglycerides are oils / melting point below body temperature;Triglycerides are oils / melting point below body temperature;• Explanation of advantage, Explanation of advantage,

– e.g. prevents hard layer of fat forming under skin / mobility e.g. prevents hard layer of fat forming under skin / mobility of lipid / deposition in arteriesof lipid / deposition in arteries..

(d) Triglycerides are broken down in the digestive system.(d) Triglycerides are broken down in the digestive system.(i) Name the enzyme that digests triglycerides.(i) Name the enzyme that digests triglycerides.• LipaseLipase..(ii) Name one organ which produces this enzyme.(ii) Name one organ which produces this enzyme.• Pancreas/salivary glands/small intestinePancreas/salivary glands/small intestine