8 3 The diagram shows two amino acids found in the primary sequence of collagen. N C C H H O O H H H N C C CH3 H O O H H H glycine alanine (a) (i) Which is the R-group for alanine? (1) A CH3 B COOH C H D NH2 (ii) Draw the products of a condensation reaction between glycine and alanine. (2) Turn over 9 (iii) Describe the structure of collagen. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 10 (b) Ehlers-Danlos syndrome is a human condition caused by a mutation in a collagen gene. This causes changes to the elasticity and strength of arteries. Mice were genetically modified to have this mutation. The elastic constant and force required to break arteries from genetically modified mice and unmodified mice were measured. The elastic constant is calculated by using the formula: elastic constant = force applied increase in length of artery The results are shown in the table. Artery Elastic constant / N mm−1 Force required to break artery / N unmodified mice 0.26 2.0 genetically modified mice 0.12 1.6 Turn over 11 (i) Calculate the force required to produce an increase in length of 0.5 cm for an artery taken from an unmodified mouse. (1) Answer.............................................................. (ii) People with Ehlers-Danlos syndrome are at risk of developing aneurysms. An aneurysm is an area of artery wall that weakens and can burst. Explain why people with Ehlers-Danlos syndrome have a high risk of aneurysms. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 3 = 10 marks)