Question

1 Explain the meaning of the term mutarotation.

2 Draw the structure of a disaccharide made up of two D-glucose units. The glycosidic bond is

    α-1,6-glycosidic bond.

3 Trehalose is a disaccharide that can be obtained from fungi, sea urchins and insects. Acid hydrolysis of

    trehalose yields only D-glucose. Trehalose is hydrolysed by α-glucosidase and not by β-glucosidase

    enzymes. Methylation of trehalose followed by hydrolysis yields two molar equivalents of

    2,3,4,6-tetra-O-methyl-D-glucopyranose.

1.   From the following experimental data, deduce the structure of trehalose.
2. What will be the effect of trehalose on Fehling’s solution?

4(a) Suggest a test you will use to show that a given food substance contains protein.

2. Show how you will use

1. Modified Gabriel’s Synthsis
2. Streckers’s Synthesis   to prepare phenylalanine in the laboratory.

5 (a) Describe in detail how you will determine the primary structure of protein.

(b) You have been given a mixture of lysine, histidine and cysteine. The isoelectric point of the amino acids are as follows:

Histidine                        7.64

Lysine                             9.74

Cystenie                         5.02

Show how you will separate the mixture into the pure forms. State and describe any instrument that you will use to separate the components in the mixture.

6 (a) A decapeptide has the following amino acid composition:

         Ala₂ , Arg, Cys, Glu, Gly, Leu, Lys, Phe, Val

       Partial hydrolysis yields the following tripeptides:

       Cys-Glu-Leu + Gly-Arg-Cys + Leu-Ala-Ala+ Lys-Val-Phe + Val-Phe-Gly.

       Reaction of the decapeptide with 2,4-dinitrofluorobenzene yields 2,4-dinitrophenylysine. From the

       experimental data, deduce the primary structure of the decapeptide.

   (b) Suggest a scheme you will follow to synthesize the dipeptide Ala-Gly

Answer 1

Mutarotation is the property of the sugar having a hemiacetal group.The alpha and beta anomer (differ in the OH group at the C1 position )of glucopyranose differ from each other in the direction of the plane polarised light rotation. The alpha glucopyranose rotate the plane polarised light to +112 degree and the beta glucopyranose rotate the plane polarised light to +18.7 degree.Now if we place either the alpha or beta anomers of glucopyranose into the solution then rotation changes eventually until reached at 52.7 degree.This is called as mutarotation.The specific rotation of alpha glucopyranose is decreased from 112 to 52.7 whereas that of beta pyranose is increased from 18.7 to 52.7.

The reason for the mutarotation is that the cyclic carbohydrate exist in equilibrium with open straight chain counterpart.When we place the alpha anomer into the solution it will open up to straight chain and then the straight chain will form the close chain but it can form both the alpha and the beta anomer .Therefore eventually the alpha and the beta anomer equilibriate and mixture of both the alpha and the beta produce a mutarotation of 52.7.

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