JEE Chemistry Biomolecules MCQs Set 28

Answer: (d) a, b

Explanation:
1. The amino group sits on the carbon next to COOH, so it is an α-amino acid.
2. It has two amino groups and one carboxyl group, so it is basic.
3. Lysine is an essential amino acid, so the body cannot synthesise it.
4. Answer: (d)

Teacher's Note:
1. Link each biomolecule with its structure and characteristic reaction; most questions here are direct recall of these links.

Answer: (c) The pentaacetate of glucose does not react with hydroxylamine

Explanation:
1. The oxime formation and bromine water oxidation show a free CHO group (open chain).
2. The pentaacetate not reacting with NH₂OH shows that the CHO group is absent, because it is tied up in the cyclic hemiacetal form.
3. Answer: (c)

Teacher's Note:
1. Link each biomolecule with its structure and characteristic reaction; most questions here are direct recall of these links.

Answer: (b) 5 HCOOH + HCHO

Explanation:
1. Periodic acid cleaves each C–C bond between carbons carrying OH or C=O groups.
2. The CHO carbon and the four CHOH carbons each end up as HCOOH (5 in all).
3. The terminal CH₂OH carbon becomes HCHO.
4. Answer: (b)

Teacher's Note:
1. Link each biomolecule with its structure and characteristic reaction; most questions here are direct recall of these links.

Answer: (a) Thyroxine

Explanation:
1. Thyroxine, secreted by the thyroid gland, is an iodinated amino acid derivative.
2. Deficiency of iodine therefore causes goitre.
3. Answer: (a)

Teacher's Note:
1. Link each biomolecule with its structure and characteristic reaction; most questions here are direct recall of these links.

Answer: (b) Anomers

Explanation:
1. They differ only in the configuration at C-1, the new stereocentre formed on ring closure.
2. Cyclic sugars that differ only at the anomeric carbon are called anomers.
3. Answer: (b)

Teacher's Note:
1. Link each biomolecule with its structure and characteristic reaction; most questions here are direct recall of these links.

Answer: (a) 2,4-DNP

Explanation:
1. Tollens' and Fehling's reagents are given through the free CHO group in the open-chain form.
2. In the cyclic form the carbonyl is a hemiacetal, and the open-chain aldehyde is present in too small an amount to give a 2,4-DNP precipitate (and glucose also fails Schiff's test).
3. Answer: (a)

Teacher's Note:
1. Link each biomolecule with its structure and characteristic reaction; most questions here are direct recall of these links.

Answer: (d) All of these

Explanation:
1. In solution the α-form interconverts with the β-form through the open-chain aldehyde, which is mutarotation.
2. The same small amount of open-chain form reduces Tollens' reagent, yet it is too little to give a 2,4-DNP test.
3. All three statements are correct.
4. Answer: (d)

Teacher's Note:
1. Link each biomolecule with its structure and characteristic reaction; most questions here are direct recall of these links.

Answer: (a) Mercurous and mercuric nitrate in HNO₃

Explanation:
1. Millon's reagent is a solution of mercurous and mercuric nitrates in nitric acid.
2. It tests for the phenolic group of tyrosine in proteins.
3. Answer: (a)

Teacher's Note:
1. Link each biomolecule with its structure and characteristic reaction; most questions here are direct recall of these links.

Answer: (d) α-Amino acids

Explanation:
1. Proteins are hydrolysed by enzymes through proteoses, peptones and peptides.
2. The final stage gives free α-amino acids, which are absorbed.
3. Answer: (d)

Teacher's Note:
1. Link each biomolecule with its structure and characteristic reaction; most questions here are direct recall of these links.

Answer: (d) Proteins (essential amino acids)

Explanation:
1. Kwashiorkor is a form of protein-energy malnutrition in children.
2. It arises from a lack of dietary protein, that is of essential amino acids.
3. Answer: (d)

Teacher's Note:
1. Link each biomolecule with its structure and characteristic reaction; most questions here are direct recall of these links.