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.

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$-\text{COO}^- \rightarrow -\text{COOH}$), 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.

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

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

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

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

Related Formula

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$\text{Alanine} + HNO_2 \rightarrow \text{Lactic acid} + N_2\uparrow + H_2O$
• 2 × Glycine Δ Cyclic diketopiperazine + 2H₂O$2 \times \text{Glycine} \xrightarrow{\Delta} \text{Cyclic diketopiperazine} + 2H_2O$

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