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7 - Surname Given name Number p 8 8 Homocysteine is an...

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Unformatted text preview: Surname: Given name: Number: p. 8 8. Homocysteine is an amino acid, although it is not normally found in proteins. Currently, there is great interest in this compound, because of evidence that it can irritate blood vessels, leading to blockages in the arteries (atherosclerosis). Elevated blood levels of homocysteine may predict a person’s risk of heart attack. Homocysteine is a thiol (mercaptan) and its structure is just like that of cysteine, except that it has two methyl groups (beta and gamma) in the side chain, rather than one. a) Draw the complete structure of homocysteine. (2 marks) i J l [I O Lisfi‘lv ' o“ b) Homocysteine is formed in the body by the metabolism of another amino acid (one of the twenty found in proteins). Suggest which amino acid is the precursor of homocysteine. (I mark) ' r , .. L/ 9. Invertase, the enzyme that catalyzes the hydrolysis of sucrose (“cane sugar”) to give fructose and glucose, was one of the first enzymes discovered. In 1890, O’Sullivan and Tompson published a study of invertase, and they reported that “invertase, when in the presence of cane sugar, will stand without injury a temperature fully 25 ° higher than in its absence.” Subsequently, many other enzymes have been shown to show the same behaviour: they undergo denaturation at elevated temperatures when they are incubated in the presence of their substrates. Explain briefly why this is so. (2 marks) ...
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