Answer the following: Give one example each of fibrous protein and globular protein. The structures…
Answer the following:
(i)[1.0]
Give one example each of fibrous protein and globular protein.
(ii)[1.0]
The structures of two amino acids, glycine and alanine, are given below. Draw the peptide linkage between these two amino acids.
(iii)[1.0]
Justify that glucose is an aldose form of sugar, with the help of a chemical reaction.
Answer
Answer (i)
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Fibrous protein: Keratin (or collagen, myosin)
Globular protein: Insulin (or albumin, haemoglobin)
Answer (ii)
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The peptide linkage is the amide bond ($-\text{CO}-\text{NH}-$) formed between the carboxyl group of glycine and the amino group of alanine with elimination of a water molecule:
$\text{H}_2\text{N}-\text{CH}_2-\text{CO}-\text{NH}-\text{CH}(\text{CH}_3)-\text{COOH} + \text{H}_2\text{O}$
The characteristic linkage is:
$-\text{C}(=\text{O})-\text{NH}-$
Answer (iii)
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Glucose contains an aldehydic group ($-\text{CHO}$), as proven by its oxidation with a mild oxidizing agent such as bromine water ($\text{Br}_2 / \text{H}_2\text{O}$) to form gluconic acid (a six-carbon monocarboxylic acid), showing that the carbonyl group is an aldehyde:
$\text{CHO}-(\text{CHOH})_4-\text{CH}_2\text{OH} + [\text{O}] \xrightarrow{\text{Br}_2 / \text{H}_2\text{O}} \text{COOH}-(\text{CHOH})_4-\text{CH}_2\text{OH}$
From ISC 2026 Chemistry Paper 1, question 14.