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NEET Biology: Chemical constitution of DNA and RNA and biological functions of nucleic acids Practice Questions

14 free multiple-choice questions on Chemical constitution of DNA and RNA and biological functions of nucleic acids (Nucleic Acids) for NEET Biology, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.

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  1. Q1. The directionality of a nucleic acid strand, which dictates the orientation of the chain, is defined by which convention?

    • APhosphate to Sugar
    • B5' to 3'
    • CUpstream to Downstream
    • D3' to 5'
    Show answer & explanation

    Correct answer: B — 5' to 3'

    The directionality of nucleic acid strands is conventionally described from the 5' end to the 3' end.

  2. Q2. What is the fundamental chemical difference between DNA and RNA regarding their sugar component?

    • ADNA has phosphate while RNA does not
    • BDNA has ribose while RNA has deoxyribose
    • CDNA has deoxyribose while RNA has ribose
    • DDNA contains only pyrimidines while RNA contains purines
    Show answer & explanation

    Correct answer: C — DNA has deoxyribose while RNA has ribose

    DNA contains deoxyribose sugar, whereas RNA contains ribose sugar.

  3. Q3. Which of the following is a monomer unit of DNA and RNA?

    • AFatty acid
    • BNucleotide
    • CAmino acid
    • DMonosaccharide
    Show answer & explanation

    Correct answer: B — Nucleotide

    Nucleotides are the fundamental building blocks (monomers) of DNA and RNA.

  4. Q4. In the formation of the standard double helix structure of DNA, the hydrogen bonds between complementary base pairs are primarily responsible for which structural feature?

    • ACreating the overall stability of the helix
    • BFacilitating the phosphodiester linkage
    • CDetermining the primary sequence of transcription
    • DDetermining the directionality of the strand
    Show answer & explanation

    Correct answer: A — Creating the overall stability of the helix

    The specific arrangement of hydrogen bonds between complementary bases (A-T and G-C) is crucial for holding the two strands together to form the stable double helix structure.

  5. Q5. The structural backbone of a nucleic acid is formed by the linkage of which functional group between adjacent nitrogenous bases?

    • APhosphate group
    • BHydroxyl group
    • CCarboxyl group
    • DAmino group
    Show answer & explanation

    Correct answer: A — Phosphate group

    The backbone of DNA and RNA consists of alternating sugar and phosphate groups. The phosphate group links the sugar molecules together to form the backbone.

  6. Q6. Which of the following nucleic acids functions primarily as an intermediary in protein synthesis by carrying amino acids from the ribosome?

    • ADNA
    • BTransfer RNA (tRNA)
    • CRibosomal RNA (rRNA)
    • DMessenger RNA (mRNA)
    Show answer & explanation

    Correct answer: B — Transfer RNA (tRNA)

    tRNA (Transfer RNA) plays the crucial role in bringing specific amino acids to the ribosome during translation.

  7. Q7. Which of the following nitrogenous bases pairs with Guanine (G) in the DNA double helix structure?

    • AUracil (U)
    • BCytosine (C)
    • CThymine (T)
    • DAdenine (A)
    Show answer & explanation

    Correct answer: B — Cytosine (C)

    In DNA, Guanine always pairs with Cytosine (G-C pairing).

  8. Q8. The polarity of the sugar molecule in RNA is primarily characterized by the presence of a hydroxyl group (-OH) at which carbon position compared to DNA?

    • AC1
    • BC3
    • CC5
    • DC2
    Show answer & explanation

    Correct answer: B — C3

    Ribose (in RNA) has a hydroxyl group on the 2' carbon, while deoxyribose (in DNA) has a hydrogen atom at that position (hence the 'deoxy').

  9. Q9. The primary role of transfer RNA (tRNA) molecules in protein synthesis is to facilitate which specific process?

    • AStoring genetic information
    • BCatalyzing peptide bond formation
    • CForming the nucleoid region
    • DTransporting specific amino acids to the ribosome
    Show answer & explanation

    Correct answer: D — Transporting specific amino acids to the ribosome

    tRNA molecules act as adaptors, carrying specific amino acids to the ribosome based on the mRNA codon sequence, which is essential for polypeptide chain elongation.

  10. Q10. In RNA molecules, which nitrogenous base is typically found in place of Thymine found in DNA?

    • AGuanine
    • BAdenine
    • CUracil
    • DCytosine
    Show answer & explanation

    Correct answer: C — Uracil

    RNA contains Uracil (U) instead of Thymine (T) in its structure. This substitution is a key chemical difference between DNA and RNA.

  11. Q11. Which type of glycosidic bond links the nitrogenous bases in a nucleic acid structure?

    • APhosphodiester bond
    • BPeptide bond
    • CEster bond
    • DGlycosidic bond
    Show answer & explanation

    Correct answer: D — Glycosidic bond

    Nitrogenous bases in nucleic acids are linked by glycosidic bonds.

  12. Q12. Which component is common to both DNA and RNA molecules, forming the backbone structure?

    • ARibose sugar
    • BThymine base
    • CPhosphate group
    • DDeoxyribose sugar
    Show answer & explanation

    Correct answer: C — Phosphate group

    The backbone of both DNA and RNA is a polymer chain formed by linking the phosphate group of one nucleotide to the sugar of the next nucleotide via phosphodiester bonds. The phosphate group is a universal component of the backbone structure.

  13. Q13. The specific pairing mechanism between complementary nitrogenous bases in a DNA double helix is stabilized by which type of bonds?

    • AIonic bonds only
    • BHydrogen bonds and Van der Waals forces
    • CCovalent bonds only
    • DHydrogen bonds only
    Show answer & explanation

    Correct answer: D — Hydrogen bonds only

    The complementary pairing of A-T and G-C bases in DNA is maintained by specific hydrogen bonds, which hold the two strands together to form the double helix structure.

  14. Q14. Which of the following accurately describes the monomer unit of a nucleic acid chain?

    • APhosphodiester bond
    • BNucleotide
    • CNucleoside
    • DDeoxyribose
    Show answer & explanation

    Correct answer: B — Nucleotide

    The monomer unit that links together to form a polynucleotide chain (DNA or RNA) is the nucleotide, which consists of a nitrogenous base, a pentose sugar, and a phosphate group.

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