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Unformatted text preview: 1. CHEMISTRY HTK ASSIGNMENT 13 Draw the complete structure of the peptide: Val—Ser—Ala. Describe i) the Sanger method and ii) the Edman degradation for determining the structure of a polypeptide. Polypeptides may be analysed by complete and partial hydrolysis. Complete hydrolysis shows the mole ratio
of amino acid residues. Partial hydrolysis yields fragments which are useful in structural determination.
Determine the structures of two polypeptides from the following information: a) i) Complete hydrolysis: composition is Ala, Gly, Leu, Ser, Val, Tyr3
ii) Partial hydrolysis: fragments were Leu—Val + Ala—Gly + Val—Ser + Gly—Tyr—Leu +
Val—Ser—Tyr + Tyr—Tyr.
b) i) Complete hydrolysis: composition is Ala, Glyz, Leu, Phez, Tyr, Val.
ii) Partial hydrolysis: fragments were Ala—Phe—Tyr + Leu—Val—Phe + Gly—Gly—Leu +
Val—Phe—Ala. A polypeptide was analysed twice by partial hydrolysis. The first reaction mixture yielded the following
fragments: Arg + Val—Gly—Ser—Lys + Asp—Gln—Tyr—Ala f Ala—-Ser—Phe—Gly———Lys +
Tyr—Gly—Leu. The second reaction mixture yielded the following fragments:
Val—Gly—Ser—Lys—Ala—Ser—Phe + Ala—Arg—Tyr + Gly—Lys—Asp—Gln + Gly—Leu + Tyr. Propose a structure for the original polypeptide. Write equations for the reactions of alanine with: a) sodium hydroxide b) hydrochloric acid
c) nitrous acid d) ethanol and sulphuric acid
e) ammonia 7 f) thionyl chloride _ Write equations, indicating reagents and reaction conditions to show how the following amino acids can be
prepared from the reactants speciﬁed: a) alanine from propionic acid b) phenylalanine from 2-pheny1aceta1dehyde
c) glycine from ethanol d) phenylalanine from toluene e) leucine from isopropyl alcohol a) Starting from methyl bromide, suggest a synthesis of HZNCHZMCOOH using l4C02 as the source of
carbon—14. b) Starting from methyl bromide suggest a synthesis for HZNMCHCOOH using Na14CN as the source of
carbon-14. . l CH3
a) Describe the steps that are followed in order to synthesize a tripeptide, explaining the chemistry involved each step.
b) Write equations showing the steps and intermediates formed during the synthesis of serylalanylvaline. TURN OVER _ 2 _
9. Identify the compound which gave the following spectra:
IR Spectrum ‘ . WAVELENGYH MCDONSI 1 4 s s 7 l v m u I: II u 15
v | | l | , l l ' l IN 100 IIANSMIHANCI (M
Absorbance X 100 NMR Spectrum lnlensily m/e
Solomons and Fryhle, 7th ed., p. 1185-1225 , Nos.: 24.1, 24.6, 24.7, 24.8, 24.9, 24.11, 24.20 ...
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- Spring '08
- Organic chemistry