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Question of 110

Q.a) Write the Haworth structure of sucrose.

(2)
b) i) What are essential amino acids?
(1)
b) ii) Give an example for fibrous proteins.
(1)
c) Name the nitrogenous base present in DNA but not in RNA. (1)
Karnataka PUCKarnataka II PUC Board 2024Subjective· 5mImportance★★★★★
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Figure — Part (a) asks to write the Haworth structure of sucrose, which needs a drawn glucose-fructose ring structure;
Figure — Part (a) asks to write the Haworth structure of sucrose, which needs a drawn glucose-fructose ring structure;

Sucrose is a disaccharide of α\alpha-D-glucose and β\beta-D-fructose joined by a glycosidic linkage; essential amino acids must come from the diet; keratin is a fibrous protein; and thymine is the base present in DNA but not RNA.

a) Haworth structure of sucrose

Sucrose is formed by joining a glucose unit (α\alpha-D-glucopyranose, six-membered ring) and a fructose unit (β\beta-D-fructofuranose, five-membered ring) through a glycosidic linkage between C-1 of glucose and C-2 of fructose. The linkage is α,β\alpha,\beta-1,2 (both anomeric/reducing carbons are involved, so sucrose is a non-reducing sugar).

Haworth (described): a glucopyranose ring (with -CH2OH\text{-CH}_2\text{OH} at C-5 and -OH\text{-OH} groups) linked through an oxygen bridge from its C-1 to the C-2 of an adjacent fructofuranose ring:

α-D-glucopyranose⏟6-membered ring  -O-  β-D-fructofuranose⏟5-membered ring\underbrace{\alpha\text{-D-glucopyranose}}_{\text{6-membered ring}}\;\text{-O-}\;\underbrace{\beta\text{-D-fructofuranose}}_{\text{5-membered ring}}

i.e. α\alpha-D-glucopyranosyl-(1→2)(1\rightarrow2)-β\beta-D-fructofuranoside. …

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