Biomolecules — JEE Main practice

39 questions

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Sample questions with solutions

Q1 · 2026

Identify the correct statements.

A. Arginine and Tryptophan are essential amino acids.

B. Histidine does not contain heterocyclic ring in its structure.

C. Proline is a six membered cyclic ring amino acid.

D. Glycine does not have chiral centre.

E. Cysteine has characteristic feature of side chain as $MeS-CH_2-CH_2-$ .

Choose the correct answer from the options given below :

A.
C and D Only
B.
C and E Only
C.
A and D Only
D.
B and E Only

Answer: C

Q2 · 2026

The correct statements are :

A. Activation energy for enzyme catalysed hydrolysis of sucrose is lower than that of acid catalysed hydrolysis.

B. During denaturation, secondary and tertiary structures of a protein are destroyed but primary structure remains intact.

C. Nucleotides are joined together by glycosidic linkage between $C_1$ and $C_4$ carbons of the pentose sugar.

D. Quaternary structure of proteins represents overall folding of the polypeptide chain.

Choose the correct answer from the options given below :

A.
A, B and D Only
B.
A, C and D Only
C.
A and B Only
D.
B and C Only

Answer: C

Statement A: Enzymes, being highly specific biological catalysts, are generally far more effective than acids at lowering activation energy under physiological conditions. For sucrose hydrolysis, the enzyme sucrase substantially reduces the activation energy compared to acid catalysis, making Statement A correct.
Statement B: Denaturation disrupts the weak, non-covalent interactions (hydrogen bonds, hydrophobic interactions) that maintain secondary and tertiary structure, but the strong covalent peptide bonds forming the primary sequence remain unaffected, making Statement B correct.
Statement C: Nucleotides are actually joined by phosphodiester bonds between the 5' phosphate of one nucleotide and the 3'-OH of the pentose sugar of the next nucleotide — not by a glycosidic linkage between $C_1$ and $C_4$ . The glycosidic linkage instead connects the nitrogenous base to $C_1$ of the sugar within a single nucleotide, not between nucleotides. This makes Statement C incorrect.
Statement D: The overall folding of a single polypeptide chain describes the tertiary structure, not the quaternary structure. The quaternary structure instead describes how multiple separate polypeptide subunits assemble together. This makes Statement D incorrect. Hence, only statements A and B are correct, so the answer is option C.

Q3 · 2026

Given below are two statements :

Statement I : Sucrose is dextrorotatory. However, sucrose upon hydrolysis gives a solution having mixture of products. This solution shows laevorotation.

Statement II : Hydrolysis of sucrose gives glucose and fructose. Since the laevorotation of glucose is more than the dextrorotation of fructose, the resulting solution becomes laevorotatory.

In the light of the above statements, choose the correct answer from the options given below :

A.
Statement I is true but Statement II is false
B.
Both Statement I and Statement II are false
C.
Both Statement I and Statement II are true
D.
Statement I is false but Statement II is true

Answer: A

Sucrose has a specific rotation of $[\alpha]_D=+66.5^{\circ}$ , confirming it is indeed dextrorotatory.
Upon hydrolysis, sucrose breaks down into glucose ( $[\alpha]_D=+52.5^{\circ}$ , dextrorotatory) and fructose ( $[\alpha]_D=-92.4^{\circ}$ , strongly laevorotatory). Since fructose's laevorotation magnitude far exceeds glucose's dextrorotation, the resulting mixture is net laevorotatory — this is called inversion of sugar. This confirms Statement I is true.
However, Statement II incorrectly attributes the laevorotation to "glucose's laevorotation being more than fructose's dextrorotation" — but glucose is actually dextrorotatory, not laevorotatory, and it's fructose that is strongly laevorotatory, not dextrorotatory. This reversed attribution makes Statement II false. Hence, Statement I is true but Statement II is false, so the answer is option A.

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