SHORT ANSWER AND DISCUSSION PART 1. Knowledge of the structures and chemical pro

Question

SHORT ANSWER AND DISCUSSION PART 1. Knowledge of the structures and chemical properties of the amino acids is crucial to understanding how proteins carry out their biological functions. The structures of the side chains of 19 amino acids are given on the last page of this test (1) On the structure page at the end of the test, name (spelled correctly) the amino acid that contains each side chain shown. (2) By placing its three-letter acronym (e.g. write 'gly' for glycine) in the blank by each description, match the amino acid's R group with the most appropriate description of its properties (a) to (m). Some of the descriptions may be used more than once You probably should read all of the descriptions before you decide on your answers, in case there is a better description for a particular amino acid than the one you are considering. (a) small polar R group containing a hydroxyl group, this amino acid is important in the active site of some enzymes. (b) provides the least amount of steric hindrance. (c) R group has pKa 10.5, making it positively charged at physiological pH. (d) sulfur-containing R group, neutral at any pH. (e) aromatic R group, hydrophobic in nature and neutral at any pH. ( saturated hydrocarbon, important in hydrophobic interactions. (g) the only amino acid having an ionizing R group with a pKa near 7; it is an (h) the only amino acid having a substituted alpha amino group; it influences ) R group has a pka near 4 and thus is negatively charged at pH 7 important group in the active site of some enzymes. protein folding by forcing a bend in the chain. an aromatic R group capable of forming hydrogen bonds, it has a pHa near 10 1 continued on next page 1 continued (k) forms disulfide cross-links between polypeptide chains; the pKa of its functional group is about 10.

Explanation / Answer

2. a) Ser : its serine containing polar OH group in side chain and component of enzymes

b) Gly: glycine being the snallest amino acid provides the least steric hindrence

c) Lys : lysine has side chain pKa 10.5

d) Met: methionine containing S containing R group and neutral at any pH

e) Phe: phenyl alanine containg hydrophobic aromatic ring

f) Val: valine

g) His: histidine

h) Pro: proline

i) Glu : glutamic acid

j) Tyr: tyrosine

k) Cys: cystine

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