Kalvi.NEET

Nucleic Acids

நியூக்ளிக் அமிலங்கள்

NCERT Class 11 · Biomolecules · 8 NEET questions

DNA is not just a molecule; it is the ultimate biological blueprint. If you confuse the pentose sugar in DNA with that of RNA, you have already lost the mark. Precision in molecular structure is the only way to secure your seat.

The idea

Nucleic acids are polynucleotides formed by the polymerization of nucleotides. Each nucleotide consists of a nitrogenous base, a pentose sugar (ribose or deoxyribose), and a phosphate group. The nitrogenous bases are classified as purines (adenine, guanine) and pyrimidines (cytosine, thymine, uracil). These monomers link via phosphodiester bonds to form the genetic backbone.

Why it matters

They are responsible for the storage, transmission, and expression of genetic information in all living organisms.

NEET lens

NEET focuses on the structural differences between DNA and RNA, specifically the 2'-OH group in ribose. Expect questions on the types of nitrogenous bases and the nature of the phosphodiester linkage. Memorize the purine-pyrimidine pairing rules. Do not confuse the sugar structure; it is a high-frequency trap.

Clinical significance

Nucleic acid integrity is vital for cellular function. Mutations in DNA sequences lead to genetic disorders like Sickle Cell Anemia or Cystic Fibrosis. When DNA repair mechanisms fail, uncontrolled cell division results in oncogenesis.

Introduction

Nucleic acids (DNA and RNA) are polymers of nucleotides. DNA stores genetic information; RNA carries and translates it into protein.

Core concept

Nucleotide: nitrogenous base + pentose sugar + phosphate. DNA: deoxyribose sugar, bases A/T/G/C, double-stranded, 3'-5' antiparallel. RNA: ribose sugar, bases A/U/G/C, single-stranded. Base pairing: A-T (2 H bonds), G-C (3 H bonds) in DNA. A-U (2 H bonds) in RNA.

Go deeper

Chargaff's rules: [A] = [T], [G] = [C] in double-stranded DNA. This was key evidence for Watson-Crick double helix model. GC pairs stronger than AT (3 vs 2 H bonds) → GC-rich DNA has higher melting temperature.

From Class 10

DNA and RNA are the molecules of heredity and protein synthesis. Together they are called nucleic acids.

Previous year NEET questions (8)

  1. NEET 2023

    Given below are two statements: Statement I: A unit formed by the attachment of a base to 1' position of sugar is known as nucleoside. Statement II: When nucleoside is linked to phosphorous acid at 5'-position of sugar moiety, we get nucleotide.

    1. Statement I is false but Statement II is true.
    2. Both Statement I and Statement II are true.
    3. Both Statement I and Statement II are false.
    4. Statement I is true but Statement II is false.
    Show answer

    Answer: (D) Statement I is true but Statement II is false.

  2. NEET 2023

    Statement I: RNA mutates at a faster rate. Statement II: Viruses having RNA genome and shorter life span mutate and evolve faster.

    1. Statement I false but Statement II is true.
    2. Both Statement I and Statement II are true.
    3. Both Statement I and Statement II are false.
    4. Statement I is true but Statement II is false.
    Show answer

    Answer: (B) Both Statement I and Statement II are true.

  3. NEET 2023

    When nucleoside is linked to phosphoric acid at 5'-position of sugar moiety, we get:

    1. Polynucleotide
    2. Nucleoside
    3. Protein
    4. Nucleotide
    Show answer

    Answer: (D) Nucleotide

  4. NEET 2019

    Purines found both in DNA and RNA are

    1. Adenine and thymine
    2. Adenine and guanine
    3. Guanine and cytosine
    4. Cytosine and thymine
    Show answer

    Answer: (B) Adenine and guanine

  5. NEET 2017

    Which of the following RNAs should be most abundant in animal cell?

    1. rRNA
    2. tRNA
    3. mRNA
    4. miRNA
    Show answer

    Answer: (A) rRNA

  6. NEET 2016

    The CORRECT statement regarding RNA and DNA, is ________.

    1. the sugar component in RNA is arabinose and the sugar component in DNA is ribose
    2. the sugar component in RNA is 2'-deoxyribose and the sugar component in DNA is arabinose
    3. the sugar component in RNA is arabinose and the sugar component in DNA is 2'-deoxyribose
    4. the sugar component in RNA is ribose and the sugar component in DNA is 2'-deoxyribose
    Show answer

    Answer: (D) the sugar component in RNA is ribose and the sugar component in DNA is 2'-deoxyribose

  7. NEET 2015

    Which one of the following is not applicable to RNA?

    1. Chargaff's rule
    2. Complementary base pairing
    3. 5' phosphoryl and 3' hydroxyl ends
    4. Heterocyclic nitrogenous bases
    Show answer

    Answer: (A) Chargaff's rule

  8. NEET 2015

    Which of the following biomolecules does have a phosphodiester bond?

    1. Amino acids in a polypeptide
    2. Nucleic acids in a nucleotide
    3. Fatty acids in diglyceride
    4. Monosaccharides in a polysaccharide
    Show answer

    Answer: (B) Nucleic acids in a nucleotide

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