Problem 2
Show how the open form of D-ribose undergoes conversion to the furanose form, and comment on why the latter is classed as a hemiacetal.
Problem 3
(a) Draw the structure of the pyranose form of D-glucose and comment on what is meant by the anomeric centre. (b) Give a mechanism by which the open form of D-glucose converts to its furanose form, and suggest why this is less favourable than formation of the pyranose form.
Problem 5
Classify the following sugars as tetroses, pentoses or hexoses, and as aldoses or ketoses: (a) glucose, (b) fructose, (c) ribose, (d) mannose, (e) galactose, (f) threose.
Problem 6
Classify the following sugars as monosaccharides, disaccharides or polysaccharides: (a) cellulose, (b) lactose, (c) galactose, (d) amylose, (e) sucrose, (f) ribose, (g) fructose.
Problem 7
Explain what you understand by the following notations: (a) \(\mathrm{D}\) - and \(\mathrm{L}\) -forms of a particular sugar, (b) \(\alpha\) - and \(\beta\) -D-glucose, (c) \((R)-\) and \((S)\) glyceraldehyde.
Problem 8
(a) Draw the structure of and name the only achiral amino acid. (b) Does nature tend to use \(\mathrm{D}\) -, \(\mathrm{L}\) - or racemic amino acids? (c) Draw the structure of \((R)\) -cysteine. (d) Give the names of the amino acids for which the following are abbreviations: Val, Gly, Asp, Cys, Glu, His.
Problem 9
(a) What is meant by the zwitterionic form of an amino acid? (b) How will the structure of L-valine respond to changes in \(\mathrm{pH}\) if the \(\mathrm{p} K_{\mathrm{a}}\) of the \(\mathrm{CO}_{2} \mathrm{H}\) group is \(2.32,\) and the \(\mathrm{p} K_{\mathrm{b}}\) of the \(\mathrm{NH}_{2}\) group is \(4.38 ?\)
Problem 10
(a) In the synthesis of a dipeptide, where and why must activating and protecting groups be introduced before condensation of the two amino acids? (b) Give a scheme that shows the formation of Gly-Leu starting from suitably protected precursors, and ending with Leu at the \(C\) -terminus.
Problem 12
Comment on the following features of proteins: (a) primary structure, (b) secondary and tertiary structure, (c) quaternary structure, (d) fibrous protein, (e) globular protein.
Problem 14
(a) Distinguish between a nucleoside and a nucleotide. (b) Explain what is meant by the notation \(5^{\prime}\) -AGAGAGAGAGAAAAA-3'. (c) What is the complementary nucleic acid strand to the one given in part (b)? Give reasoning for your answer.
