Biomolecules – Nucleic Acids: NEET MCQs with Answers

15 free questions on Biomolecules – Nucleic Acids for NEET (UG), starting with previous-year NEET and AIPMT questions. Try each one, then tap Show answer for the answer and a short explanation.

Syllabus covered: Nucleic Acids: structure and function

Practise all 163 Biomolecules – Nucleic Acids questions free Take a free timed test

Question 1

Previous-year question
Which one of the following is a nucleotide? [Re-NEET 2024]
  1. Uridine
  2. Adenylic acid
  3. Guanine
  4. Guanosine
Show answer
Answer: (B) Adenylic acid
Explanation: Adenylic acid (AMP) consists of a nitrogen base, a pentose sugar and a phosphate group, so it is a nucleotide. Uridine and guanosine are nucleosides (base + sugar), while guanine is just a nitrogen base.

Question 2

Previous-year question
Purines found in both DNA and RNA are [NEET 2019]
  1. adenine and thymine
  2. adenine and guanine
  3. guanine and cytosine
  4. cytosine and thymine
Show answer
Answer: (B) adenine and guanine
Explanation: Adenine and guanine are the two purines common to DNA and RNA; thymine occurs only in DNA and uracil replaces it in RNA.

Question 3

Previous-year question
Which biomolecules have a phosphodiester bond? [AIPMT 2015]
  1. Monosaccharides in a polysaccharide
  2. Amino acids in a polypeptide
  3. Nucleic acids in a nucleotide
  4. Fatty acids in a diglyceride
Show answer
Answer: (C) Nucleic acids in a nucleotide
Explanation: In a polynucleotide, successive nucleotides are joined by a phosphate group that is esterified to the sugars of both, forming a phosphodiester bond.

Question 4

Previous-year question
DNA is composed of repeating units of [AIPMT 1991]
  1. Ribonucleosides
  2. Deoxyribonucleosides
  3. Ribonucleotides
  4. Deoxyribonucleotides
Show answer
Answer: (D) Deoxyribonucleotides
Explanation: Nucleic acids are repeating units of nucleotides. DNA is formed of repeating deoxyribonucleotides, which contain deoxyribose sugar, whereas RNA is a mixed polymer chain of ribonucleotides containing ribose sugar.  

Question 5

Previous-year question
The basic unit of nucleic acid is the [AIPMT 1991]
  1. Pentose sugar
  2. Nucleoid
  3. Nucleoside
  4. Nucleotide
Show answer
Answer: (D) Nucleotide
Explanation: Nucleic acids, both DNA and RNA, are linear mixed polymers of nucleotides and are for that reason also called polynucleotides. Each nucleotide consists of a nitrogenous base, a pentose sugar and a phosphate group.

Question 6

Previous-year question
Which is distributed more widely in a cell? [AIPMT 1992]
  1. DNA
  2. RNA
  3. Chloroplasts
  4. Spherosomes
Show answer
Answer: (B) RNA
Explanation: RNA is a single-chain polyribonucleotide that carries coded genetic information from DNA to the cytoplasm and takes part in protein synthesis. It is more common and abundant than DNA, and its six types — ribosomal, transfer, messenger, small nuclear, small cytoplasmic and genetic RNA — are distributed widely through the cell.

Question 7

Previous-year question
Adenine is a [AIPMT 1992]
  1. Purine
  2. Pyrimidine
  3. Nucleoside
  4. Nucleotide
Show answer
Answer: (A) Purine
Explanation: Nitrogenous bases are of two types, purines and pyrimidines. Purines are nine-membered double-ring bases possessing nitrogen at the 1, 3, 7 and 9 positions, and adenine and guanine belong to this group.
Doing well? Create a free account to take timed tests on this topic and see your weak areas.

Question 8

Previous-year question
Which is wrong about nucleic acids? [AIPMT 1993]
  1. DNA is single-stranded in some viruses
  2. RNA is double-stranded occasionally
  3. Length of one helix is 45 Å in B-DNA
  4. One turn of Z-DNA has 12 bases
Show answer
Answer: (C) Length of one helix is 45 Å in B-DNA
Explanation: The statement is incorrect because the pitch of one turn of the helix is 34 Å in B-DNA, 25 Å in A-DNA and 46 Å in the Z-model of DNA. In Z-DNA the sugar moieties are seen in opposite directions, and the 3–5 diester bond forms a zig-zag structure.

Question 9

Previous-year question
The nitrogenous organic base purine occurring in RNA is [AIPMT 1996]
  1. Cytosine
  2. Thymine
  3. Guanine
  4. Uracil
Show answer
Answer: (C) Guanine
Explanation: Purines are nine-membered double-ring nitrogen bases possessing nitrogen at the 1, 3, 7 and 9 positions, namely adenine and guanine. These purines are present in both DNA and RNA, so guanine is the purine among the options offered.

Question 10

Previous-year question
DNA synthesis can be specifically measured by estimating the incorporation of radiolabelled [AIPMT 1997]
  1. Uracil
  2. Adenine
  3. Thymidine
  4. Deoxyribose sugar
Show answer
Answer: (C) Thymidine
Explanation: DNA consists of deoxyribose sugar, phosphate and the bases adenine, guanine, cytosine and thymine, whereas RNA contains uracil in place of thymine. Since thymine is unique to DNA, estimating the incorporation of radiolabelled thymidine measures DNA synthesis specifically.

Question 11

Previous-year question
ATP is a [AIPMT 2000]
  1. Nucleotide
  2. Nucleosome
  3. Nucleoside
  4. Purine
Show answer
Answer: (A) Nucleotide
Explanation: A nucleotide consists of a five-carbon sugar, a phosphate group and a nitrogenous base. ATP contains the five-carbon sugar ribose, three phosphate groups and the nitrogenous base adenine, and it is therefore classed as a nucleotide.

Question 12

Previous-year question
Nucleotides are the building blocks of nucleic acids. Each nucleotide is a composite molecule formed by [AIPMT 2005]
  1. Base-sugar-phosphate
  2. Base-sugar-OH
  3. (Base-sugar-phosphate)ₙ
  4. Sugar-phosphate
Show answer
Answer: (A) Base-sugar-phosphate
Explanation: A single nucleotide is composed of a phosphate group, a five-carbon sugar which may be ribose or deoxyribose, and a nitrogenous base which may be a purine, adenine or guanine, or a pyrimidine, thymine, cytosine or uracil.

Question 13

Previous-year question
One turn of the helix in a B-form DNA is approximately [AIPMT 2006]
  1. 0.34 nm
  2. 3.4 nm
  3. 2 nm
  4. 20 nm
Show answer
Answer: (B) 3.4 nm
Explanation: B-DNA is a helical structure about 20 Å in diameter in which the distance between adjacent base pairs is 3.4 Å and there are ten base pairs in each complete turn. One turn of the helix therefore measures approximately 34 Å, that is, 3.4 nm.

Question 14

Previous-year question
The two polynucleotide chains in DNA are [AIPMT 2007]
  1. Parallel
  2. Discontinuous
  3. Antiparallel
  4. Semiconservative
Show answer
Answer: (C) Antiparallel
Explanation: In 1953 James Watson and Francis Crick proposed that a DNA molecule consists of two polynucleotide chains arranged antiparallel, that is, running in opposite directions with respect to the 5' and 3' ends of their sugar-phosphate backbones.

Question 15

Previous-year question
In the DNA molecule [AIPMT 2008]
  1. The total amount of purine nucleotides and pyrimidine nucleotides is not always equal
  2. There are two strands which run parallel in the 5'→3' direction
  3. The proportion of adenine in relation to thymine varies with the organism
  4. There are two strands which run antiparallel, one in the 5'→3' direction and the other in the 3'→5' direction
Show answer
Answer: (D) There are two strands which run antiparallel, one in the 5'→3' direction and the other in the 3'→5' direction
Explanation: In a DNA molecule the adjacent deoxyribonucleotides in a chain are joined by phosphodiester bridges that link the 5' carbon of one sugar with the 3' carbon of the next. The two polynucleotide strands run antiparallel, so that one has its phosphodiester linkages in the 5'→3' direction and the other in the 3'→5' direction.

Want more Biomolecules – Nucleic Acids questions?

E-GYAN NIDHI has 163 questions on this topic and 63,000+ in total, all free: timed CBT tests, NEET marking and instant analysis.

Register free Free Sunday Mock Test

More topics in Cell Structure and Function

↑