Biomolecules: JEE Advanced PYQ, 2007–2026

Q1 · Chemistry · Biomolecules

Most water-soluble vitamins are excreted in urine and are not stored in the body, whereas fat-soluble vitamins are stored in the liver and adipose tissue. Which of the following vitamins is water-soluble and yet stored in the liver?

• AVitamin B₁₂
• BVitamin A
• CVitamin C
• DVitamin B₆

Q2 · Chemistry · Biomolecules

Both D-glucose and D-fructose give a positive Tollens' test, but only D-glucose is oxidised by bromine water to gluconic acid. Which explanation accounts for this difference?

• AIn the basic medium of Tollens' reagent, fructose isomerises through an enediol to glucose and mannose, which have an –CHO group. Bromine water is not basic enough to bring about this change, and a ketone group is not oxidised by it.
• BFructose has a free –CHO group in its open chain, but bromine water is too weak an oxidant to oxidise it, whereas Tollens' reagent is strong enough.
• CTollens' reagent is a stronger oxidant than bromine water and directly cleaves the C1–C2 bond next to the ketone group in fructose, giving a silver mirror.
• DFructose exists only as the cyclic furanose form, whose free hemiketal –OH reacts with Tollens' reagent, while bromine water reacts only with open-chain forms.

Q3 · Chemistry · Biomolecules

D-Glucose is oxidised separately with (i) bromine water and (ii) concentrated nitric acid. How many –COOH groups does the main product of each reaction contain, in the order (i), (ii)?

• A1 and 2
• B2 and 1
• C1 and 1
• D2 and 2

Q4 · Chemistry · Biomolecules

Which of the following sets lists one hormone each from the steroid, polypeptide and amino-acid-derivative classes, in that order?

• ATestosterone, glucagon, thyroxine
• BGlucagon, estradiol, adrenaline
• CCortisol, thyroxine, insulin
• DProgesterone, oxytocin, cortisol

Q5 · Chemistry · Biomolecules

Thyroxine, the principal hormone of the thyroid gland, is best described as:

• Aa steroid synthesised from cholesterol
• Ban iodine-containing derivative of the amino acid tyrosine
• Ca long polypeptide chain of more than fifty amino acid residues
• Dan iodine-containing derivative of the amino acid tryptophan

Q6 · Chemistry · Biomolecules

Three patients show the following deficiency symptoms: Patient 1 has convulsions, Patient 2 has pernicious anaemia, and Patient 3 has increased blood clotting time. Which option correctly names the vitamins deficient in Patients 1, 2 and 3 respectively, and correctly states how many of these three vitamins are fat-soluble?

• AB₆, B₁₂, K; one of the three is fat-soluble
• BB₆, B₁₂, K; two of the three are fat-soluble
• CB₁, B₁₂, K; one of the three is fat-soluble
• DB₆, B₁₂, E; one of the three is fat-soluble

Q7 · Chemistry · Biomolecules

A patient shows convulsions that are traced to a vitamin deficiency. Which option names the deficient vitamin and a dietary source that supplies it?

• AVitamin B₆ (pyridoxine) – yeast, egg yolk, cereals and gram
• BVitamin B₁₂ (cobalamin) – meat, fish, egg and curd
• CVitamin B₁ (thiamine) – yeast, milk, green vegetables and cereals
• DVitamin K – green leafy vegetables

Q8 · Chemistry · Biomolecules

A dilute solution of a globular protein is heated until it turns cloudy and a white coagulate separates, as when egg white is boiled. The protein is not treated with any acid, base or enzyme. Which of the following correctly describes the change?

• AHydrogen bonds and other weak interactions that maintain the secondary and tertiary structures are disrupted, but the amino acid sequence and the peptide bonds are unchanged.
• BThe peptide bonds are hydrolysed by the heat, so the protein breaks down into free α-amino acids that are insoluble in water.
• COnly the quaternary structure is lost, while the α-helix and β-sheet regions and the tertiary fold stay intact.
• DThe primary structure is altered because the sequence of amino acids is scrambled by heating, so the protein can never regain its original sequence.

Q9 · Chemistry · Biomolecules

Fructose is a ketohexose, yet it reduces Tollens' reagent. Which of the following best explains this?

• AIn the alkaline medium of the reagent, fructose undergoes enediol rearrangement to form aldohexoses such as glucose, which are then oxidised.
• BThe ketonic C=O group of fructose is oxidised directly by Tollens' reagent to a –COOH group at the same carbon.
• CThe primary –CH₂OH group of fructose is oxidised by the reagent to –CHO, which then reduces silver ions.
• DThe cyclic hemiketal form of fructose opens to give a free –CHO group at C1 directly, without any rearrangement.

Q10 · Chemistry · Biomolecules

A synthetic double-stranded DNA fragment is 6 base pairs long. Assume each of its 12 nucleotides was built from a free nitrogenous base, 2-deoxyribose and phosphoric acid, using only condensation steps. These are: base + sugar → nucleoside, nucleoside + phosphoric acid → nucleotide (one phosphate ester each), and nucleotide + nucleotide → phosphodiester link within a strand. How many water molecules are released in building the fragment? (Hydrogen bonds between the strands release no water.)

• A36
• B35
• C34
• D22