Biomolecules JEE Main previous year questions with solutions

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1. Q1JEE Main 2026 (08 Apr, Shift 2)Carbohydrates
   The incorrect statement from the following with respect to carbohydrates is:
   1. A.All monosaccharides are reducing sugars.
   2. B.The monosaccharide units obtained from hydrolysis of oligosaccharides are always the same.
   3. C.Starch and cellulose are typical examples of polysaccharides, which are very high molecular weight compounds of more than ten monosaccharide units.
   4. D.Open chain and cyclic structures co-exist at equilibrium that are responsible for certain properties as in the case of $D-(+)$-glucose.
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   Answer: (B)

   Statement (A) is correct because all monosaccharides contain a free aldehyde or ketonic group (or exist in equilibrium with it) and act as reducing sugars. Statement (B) is incorrect because the hydrolysis of oligosaccharides can yield either the same or different monosaccharide units. For example, sucrose is an oligosaccharide (disaccharide) that yields one molecule of glucose and one molecule of fructose upon hydrolysis, whereas maltose yields two molecules of glucose. Statement (C) is correct as polysaccharides like starch and cellulose are high molecular weight polymers containing more than ten monosaccharide units. Statement (D) is correct because in an aqueous solution, $D-(+)$-glucose exists in an equilibrium between its open-chain form and its cyclic hemiacetal forms ($\alpha$ and $\beta$ anomers), which explains its mutarotation and other properties. Answer: The monosaccharide units obtained from hydrolysis of oligosaccharides are always the same.
2. Q2JEE Main 2025 (07 Apr, Shift 1)Disaccharides and Polysaccharides
   Given below are two statements: Statement I : D-(+)-glucose $+\mathrm{D}-(+)$ fructose $\xrightarrow{-\mathrm{H}_2 \mathrm{O}}$ sucrose Statement II : Invert sugar is formed during sucrose hydrolysis. In the light of the above statements, choose the correct answer from the options given below -
   1. A.Both Statement I and Statement II are true.
   2. B.Statement I is false but Statement II are true.
   3. C.Statement I is true but Statement II is false.
   4. D.Both Statement I and Statement II are false.
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   Answer: (B)

   On hydrolysis of sucrose gives D-(+)-glucose and D-(-)-fructose while in St. (1) D-(+)-fructose is given evince St-(1) is incorrect. St. II - It is correct because sucrose on hydrolysis gives invert sugar
3. Q3JEE Main 2024 (30 Jan, Shift 2)Nucleic Acids
   The total number of correct statements, regarding the nucleic acids is _________. A. RNA is regarded as the reserve of genetic information. B. DNA molecule self-duplicates during cell division C. DNA synthesizes proteins in the cell. D. The message for the synthesis of particular proteins is present in DNA E. Identical DNA strands are transferred to daughter cells.
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   Answer: 3

   A. RNA (ribonucleic acid) is not typically regarded as the reserve of genetic information in the same way that DNA (deoxyribonucleic acid) is. While RNA does play important roles in gene expression, protein synthesis, and regulation of cellular processes, it is DNA that is traditionally considered the primary repository of genetic information in cells. B. DNA molecule self-duplicates during cell division. (True) DNA (deoxyribonucleic acid) self-duplicates during cell division through a process called DNA replication. DNA replication is a fundamental process that ensures each daughter cell receives an identical copy of the genetic information from the parent cell. C. While DNA contains the genetic instructions necessary for synthesizing proteins, it does not directly synthesize proteins itself. Instead, the process by which proteins are synthesized from the genetic information encoded in DNA involves several steps and intermediates, collectively known as the central dogma of molecular biology. D. The message for the synthesis of particular proteins is present in DNA. (True) The message for the synthesis of particular proteins is present in DNA in the form of a specific sequence of nucleotide bases. This sequence is transcribed into mRNA, which carries the genetic information to the ribosomes for translation into a specific sequence of amino acids, ultimately leading to the synthesis of a particular protein. E. Identical DNA strands are transferred to daughter cells. (True) Identical DNA strands are transferred to daughter cells through the processes of DNA replication, chromosome segregation, and cell division. These processes ensure that each daughter cell receives a complete and identical set of genetic information from the parent cell.
4. Q4JEE Main 2023 (30 Jan, Shift 2)Properties and Preparation of Amino Acids
   A short peptide on complete hydrolysis produces $3$ moles of glycine $\left(G\right)$, two moles of leucine $\left(L\right)$ and two moles of valine $\left(V\right)$ per mole of peptide. The number of peptide linkages in it are _____ .
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   Answer: 6

   Peptide linkage is also known as peptide bond. It is an amide formed between $-COOHand-{NH}_{2}$ group by elimination of a water molecule. It is represented as $-CO-NH-$. Number of peptide linkages $=($Total amino acids $-1)$ Now, given that short peptide on hydrolysis give seven amino acids. $=7-1=6$
5. Q5JEE Main 2022 (29 Jul, Shift 1)Proteins
   In a linear tetrapeptide (Constituted with different amino acids), (number of amino acids) - (number of peptide bonds) is
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   Answer: 1

   A tetrapeptide is a peptide, classified as an oligopeptide, since it only consists of four amino acids joined by peptide bonds. A peptide bond, also referred to as an amide bond, is formed between the α-nitrogen atom of one amino acid and the carbonyl carbon of a second. Example of tetrapeptide is: $Tuftsin\left\{(L-threonyl)-(L-lysyl)-(L-prolyl)-(L-arginine)\right\}$is a peptide related primarily to the immune system function As we can see in this example No. of Amino Acids $=4$ No. of Peptide bonds $=3$ Hence, (number of amino acids) - (number of peptide bonds) $=1$