A-LevelBiologyBiological molecules9700/23 · May/June 2024 · Q210 Marks

Collagen is a fibrous protein that is found in many tissues in animals.

(a)Describe the structure of a collagen molecule and the structure of a collagen fibre. collagen molecule collagen fibre[5]
(b)Some amino acids in collagen can be modified to improve the stability of the protein. For example, the amino acid lysine can be modified to form hydroxylysine. Fig. 2.1 shows a disaccharide bonded to the amino acid hydroxylysine in a collagen molecule. The disaccharide is made from two monosaccharides, which are indicated by the labels D and E in Fig. 2.1. [Figure 2.1]
(b)(i)Give the precise name of the monosaccharide labelled D in Fig. 2.1.[1]
(b)(ii)On Fig. 2.1, label the glycosidic bond with the letter G. Write your answer on Fig. 2.1.[1]
(b)(iii)On Fig. 2.1, draw a circle around the R group of hydroxylysine and label the circle with the letter R. Write your answer on Fig. 2.1.[1]
(c)Osteogenesis imperfecta is a disease that results from a deficiency in collagen. Suggest how a named tissue or structure is affected in a person who has this disease.[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

[5] max 1 in molecule section if mps from collagen fibre included as features of a molecule
max 1 in fibre section if mps from molecule included as features of collagen fibre or if polypeptide described in molecule section and all features in fibre section are descriptive for a collagen molecule
any five from:
molecule (to max 4)
1 three, helical / AW, polypeptides / chains I quaternary structure or triple helix;
2 (helical chains) tightly wound ;
3 hydrogen bonds between, polypeptides / chains ;
4 (generally) every third amino acid (in each, polypeptide / chain) is glycine ;
fibre (to max 4)
5 cross links / covalent bonds, between molecules ;
6 molecules arranged in parallel ;
7 molecules (in fibril / fibre) are, staggered / ends not aligned / AW ;
8 AVP; e.g. detail of H bonds collagen fibre can be composed of collagen fibrils made of (parallel) collagen molecules glycosylated (amino acids in polypeptide) / hydroxylated
[1] a-glucose / alpha glucose ;
[1] label to glycosidic bond labelled G ;
[1] NH2CH2CHCH2CH2 circled and labelled R ;
[2] correct named tissue or structure;
e.g. blood vessels / cartilage / bone / ligaments / skin / tendons
(is/are) weaker / deformed / easily broken / AW ; A description of how function is affected

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