The carbohydrates "Ribose" present in DNA, is A. A pentose sugar B. present in pyranose from C. in "D" configuration D. a reducing sugar, when free E. in alpha -anomeric form Choose the correct answer from the options given below:

The specific carbohydrate residue present across backbone units in DNA molecules is beta-2-deoxy-D-ribose. Its spatial parameters satisfy the following conditions: - It is a 5-carbon pentose sugars skeleton structure (A). - It maintains a canonical D configuration pathway sequence (C). - When localized in free, open unlinked molecular solutions, it standardly functions as a reducing carbohydrate assembly agent (D). - It exists predominantly in a furanose cycle form inside DNA, rather than a pyranose ring. Ribose in nucleic acids occurs primarily as a five-membered furanose ring configuration system. Class 12 Chemistry: Biomolecules

The carbohydrates "Ribose" present in DNA, is A. A pentose sugar B. present in pyranose from C. in "D" configuration D. a reducing sugar, when free E. in alpha -anomeric form Choose the correct answer

The specific carbohydrate residue present across backbone units in DNA molecules is beta-2-deoxy-D-ribose. Its spatial parameters satisfy the following conditions: - It is a 5-carbon pentose sugars skeleton structure (A). - It maintains a canonical D configuration pathway sequence (C). - When localized in free, open unlinked molecular solutions, it standardly functions as a reducing carbohydrate assembly agent (D). - It exists predominantly in a furanose cycle form inside DNA, rather than a pyra

The carbohydrates "Ribose" present in DNA, is A. A pentose sugar B. present in pyranose from C. in "D" configuration D. a reducing sugar, when free E. in alpha -anomeric form Choose the correct answer from the options given below:

The specific carbohydrate residue present across backbone units in DNA molecules is beta-2-deoxy-D-ribose. Its spatial parameters satisfy the following conditions: - It is a 5-carbon pentose sugars skeleton structure (A). - It maintains a canonical D configuration pathway sequence (C). - When localized in free, open unlinked molecular solutions, it standardly functions as a reducing carbohydrate assembly agent (D). - It exists predominantly in a furanose cycle form inside DNA, rather than a pyranose ring. Ribose in nucleic acids occurs primarily as a five-membered furanose ring configuration system. Class 12 Chemistry: Biomolecules

The carbohydrates "Ribose" present in DNA, is A. A pentose sugar B. present in pyranose from C. in "D" configuration D. a reducing sugar, when free E. in alpha -anomeric form Choose the correct answer

The specific carbohydrate residue present across backbone units in DNA molecules is beta-2-deoxy-D-ribose. Its spatial parameters satisfy the following conditions: - It is a 5-carbon pentose sugars skeleton structure (A). - It maintains a canonical D configuration pathway sequence (C). - When localized in free, open unlinked molecular solutions, it standardly functions as a reducing carbohydrate assembly agent (D). - It exists predominantly in a furanose cycle form inside DNA, rather than a pyra

The carbohydrates "Ribose" present in DNA, is A. A pentose sugar B. present in pyranose from C. in "D" configuration D…

Year	2026	2025	2024	Total
Questions	9	19	8	36

Q jee_main_2025_08_april_evening Amino Acids

The chemical structure of the amino acid Valine is monitored across different environments: Choose the correct option depicting the structures of products A and B under pH = 2 and pH = 10 conditions respectively.

Valine pH equilibrium conversion layout for Q39 — The flowchart maps the structural modifications of Valine when treated at strongly acidic (pH = 2) versus basic (pH = 10) conditions.

A.
B.
C.
D.

Solution

Core Logic

Amino acids exhibit amphoteric behavior due to the simultaneously present basic amino ( $-NH₂$ $-\text{NH}_2$) and acidic carboxyl ( $-COOH$ $-\text{COOH}$) functional groups:

At pH = 2 (Highly Acidic Medium):

The abundant concentration of hydronium ions ( $H^+$ $H^+$) protonates the carboxylate ion back into its non-ionized acid state ( $-COO^- arrow -COOH$ ), while the amine group remains securely protonated as an ammonium ion ( $-NH₃^+$ $-\text{NH}_3^+$). Hence, product A exists purely as a cation.

At pH = 10 (Highly Basic Medium):

The high concentration of hydroxide ions ( $OH^-$ $OH^-$) abstracts protons from the system, deprotonating the carboxyl group into a carboxylate anion ( $-COO^-$ $-\text{COO}^-$) and neutralizing the ammonium group back into a free amine fraction ( $-NH₂$ $-\text{NH}_2$). Hence, product B exists purely as an anion.

Protonation state structures of Valine across the pH spectrum — The flowchart maps the structural modifications of Valine when treated at strongly acidic (pH = 2) versus basic (pH = 10) conditions.

Pattern Recognition

Acidic environments (low pH) force positive overall charges onto amino structures (cation form). Basic environments (high pH) drive a net negative structure (anion form). This simple rule makes picking Option (1) immediate.

Chapter Mix

Class 12 Chemistry: Biomolecules

Q29 jee_main_2025_29_jan_evening Amino Acids and Proteins

Identify the essential amino acids from below: (A) Valine (B) Proline (C) Lysine (D) Threonine (E) Tyrosine Choose the correct answer from the options given below:

A. (A), (C) and (D) only
B. (A), (C) and (E) only
C. (B), (C) and (E) only
D. (C), (D) and (E) only

Solution

Core Logic

Essential amino acids cannot be synthesized by the body and must be obtained from diet. From the given choices:

Valine (Essential)
Proline (Non-essential)
Lysine (Essential)
Threonine (Essential)
Tyrosine (Non-essential)

Hence, (A), (C), and (D) are the essential amino acids.

Pattern Recognition

Mnemonic for essential amino acids: TV TILL PM MALL (Threonine, Valine, Tryptophan, Isoleucine, Leucine, Lysine, Phenylalanine, Methionine, Arginine, Histidine).

Chapter Mix

Class 12 Chemistry: Biomolecules

Q45 jee_main_2025_28_jan_morning Reactions of Glucose and Starch

Given below are two statements : Statement I : D-glucose pentaacetate reacts with 2, 4-dinitrophenylhydrazine. Statement II : Starch, on heating with concentrated sulfuric acid at

100°C

and 2-3 atmosphere pressure produces glucose. In the light of the above statements, choose the correct answer from the options given below

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

Solution

Core Logic

Statement I is false because glucose pentaacetate fixes the cyclic hemiacetal system structure securely into an unreactive ester configuration. As a result, it cannot revert to an open-chain form containing a free aldehyde group, meaning it does not react with carbonyl reagents like 2,4-DNP.

Statement II is true because starch, a polysaccharide composed of glucose monomer blocks, undergoes acid-catalyzed hydrolysis to yield glucose when heated under pressure.

Pattern Recognition

Sees: Pentacetate reactivity vs polysaccharide hydrolysis. Shortcut: Acetylation locks the cyclic structure of glucose, preventing reactions that require an open-chain carbonyl group (like 2,4-DNP).

Chapter Mix

Class 12 Chemistry: Biomolecules

Q31 jee_main_2025_03_april_morning Carbohydrate Structures

Which of the following is the correct structure of L-fructose?

A. Structure (1)
B. Structure (2)
C. Structure (3)
D. Structure (4)

Solution

Related Formula

D- and L-enantiomers are non-superimposable mirror images of each other at all chiral centers.

Core Logic

D-fructose has the $-OH$ $-\mathrm{OH}$ group at C-5 positioned on the right in its Fischer projection. L-fructose is the exact enantiomer (mirror image) of D-fructose, meaning all chiral centers (C-3, C-4, C-5) have inverted configurations, with the $-OH$ $-\mathrm{OH}$ group at C-5 on the left.

Step 1: Structural Verification

Structure (3) correctly displays the Fischer projection of L-fructose with C-3 $-OH$ $-\mathrm{OH}$ on the right, and C-4, C-5 $-OH$ $-\mathrm{OH}$ groups on the left.

Pattern Recognition

L-isomer is the exact mirror image of the D-isomer across all stereocenters.

Chapter Mix

Class 12 Chemistry: Biomolecules

Q jee_main_2025_04_april_evening Amino Acids and Peptides

A dipeptide, "x" on complete hydrolysis gives "y" and "z". "y" on treatment with aq.

HNO₂

produces lactic acid. On the other hand "z" on heating gives the following cyclic molecule. Based on the information given, the dipeptide X is:

Cyclic molecule from dipeptide residue heating for Q29 - JEE Main 2025 Evening — The image shows a heterocyclic six-membered cyclic molecule containing amide groups, formed by heating amino acid residue z.

A. valine-glycine
B. alanine-glycine
C. valine-leucine
D. alanine-alanine

Solution

Related Formula

Dipeptide X Hydrolysis Amino Acid y + Amino Acid z

Core Logic

Since y reacts with nitrous acid ( $HNO₂$ $HNO_2$) to give lactic acid ( $CH₃-CH(OH)-COOH$ $CH_3-CH(OH)-COOH$), y must be alanine ( $CH₃-CH(NH₂)-COOH$ $CH_3-CH(NH_2)-COOH$).
When glycine ( $NH₂-CH₂-COOH$ $NH_2-CH_2-COOH$) is heated, two molecules undergo intermolecular cyclization to produce a six-membered diketopiperazine ring as shown in the problem diagram. Therefore, z is glycine.

Hence, combining residue y (alanine) and z (glycine), the dipeptide X is alanine-glycine.

Step 1: Stepwise Degradation Overview

Reaction scheme:

Alanine-Glycine linkage $arrow$ $\rightarrow$ Alanine + Glycine
$Alanine + HNO₂ arrow Lactic acid + N₂ + H₂O$
$2 \times Glycine Δ Cyclic diketopiperazine + 2H₂O$

Pattern Recognition

Lactic acid generation from alpha-amino acids via nitrous acid deamination is a definitive chemical fingerprint for alanine. The unsubstituted cyclic diketopiperazine product confirms glycine as the second component.

Chapter Mix

Class 12 Chemistry: Biomolecules

The carbohydrates "Ribose" present in DNA, is A. A pentose sugar B. present in pyranose from C. in "D" configuration D. a reducing sugar, when free E. in α$\alpha$ -anomeric form Choose the correct answer from the options given below:

Solution & Explanation

Core Logic

Pattern Recognition

Chapter Mix

Reference Study Guides

More Biomolecules Previous-Year Questions — Page 4

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Core Logic

Pattern Recognition

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Core Logic

Pattern Recognition

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Solution

Related Formula

Core Logic

Step 1: Structural Verification

Pattern Recognition

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Solution

Related Formula

Core Logic

Step 1: Stepwise Degradation Overview

Pattern Recognition

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The carbohydrates "Ribose" present in DNA, is A. A pentose sugar B. present in pyranose from C. in "D" configuration D. a reducing sugar, when free E. in $α$ $\alpha$ -anomeric form Choose the correct answer from the options given below: