Nucleic Acids Practice Questions
20 free Nucleic Acids practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
The building blocks of nucleic acids are called:
- A Amino acids
- B Nucleosides
- C Nucleotides
- D Fatty acids
Correct answer: Nucleotides
Nucleic acids like DNA and RNA are polymers made up of repeating units called nucleotides. Each nucleotide consists of a heterocyclic compound, a monosaccharide, and phosphoric acid.
A nucleoside is formed by the combination of which two components?
- A Nitrogenous base and Phosphate group
- B Pentose sugar and Phosphate group
- C Amino acid and Glucose
- D Nitrogenous base and Pentose sugar
Correct answer: Nitrogenous base and Pentose sugar
A nucleoside consists of a nitrogenous base linked to a pentose sugar (ribose or deoxyribose). When a phosphate group is attached to the nucleoside, it becomes a nucleotide.
Which of the following nitrogenous bases is a Purine?
- A Cytosine
- B Uracil
- C Adenine
- D Thymine
Correct answer: Adenine
Nitrogenous bases are divided into two types: purines and pyrimidines. Adenine and Guanine are substituted purines, characterized by a double-ring structure.
Which pyrimidine is found ONLY in RNA and not in DNA?
- A Thymine
- B Cytosine
- C Guanine
- D Uracil
Correct answer: Uracil
DNA contains the pyrimidines Cytosine and Thymine. In RNA, Thymine is replaced by Uracil, while Cytosine remains common to both.
The sugar found in DNA is a five-carbon monosaccharide known as:
- A 2-deoxyribose
- B Ribose
- C Glucose
- D Fructose
Correct answer: 2-deoxyribose
DNA stands for Deoxyribonucleic Acid because its pentose sugar is 2-deoxyribose. In RNA, the sugar is ribose, which has a hydroxyl group at the 2' carbon.
The famous double-helix model of DNA structure was proposed by:
- A Watson and Crick
- B Miescher
- C Griffith
- D Hershey and Chase
Correct answer: Watson and Crick
James Watson and Francis Crick proposed the double-helix model for the structure of DNA in 1953. Their model was based on X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin.
In the DNA double helix, the two strands are held together by:
- A Covalent bonds
- B Ionic bonds
- C Hydrogen bonds
- D Phosphodiester bonds
Correct answer: Hydrogen bonds
The nitrogenous bases of the two strands pair through hydrogen bonds. Adenine pairs with Thymine (2 bonds), and Guanine pairs with Cytosine (3 bonds).
The 'backbone' of a nucleic acid strand is formed by:
- A Nitrogenous bases
- B Hydrogen bonds
- C Sugar-phosphate
- D Peptide bonds
Correct answer: Sugar-phosphate
The structural framework of a DNA or RNA strand is the sugar-phosphate backbone. The nitrogenous bases are projected more or less perpendicular to this backbone.
Which of the following describes the 'Antiparallel' nature of DNA?
- A One strand runs 5'→3', the other 3'→5'
- B Both strands run in 5' to 3' direction
- C The strands are parallel but far apart
- D The strands rotate in the same direction
Correct answer: One strand runs 5'→3', the other 3'→5'
The two polynucleotide chains of DNA have anti-parallel polarity. This means if one strand has the polarity 5'→3', the other has 3'→5'.
According to Chargaff's rule, in a double-stranded DNA molecule:
- A A + T = G + C
- B A / T = G / C = 1
- C A + G = T + C
- D Both (b) and (c)
Correct answer: Both (b) and (c)
Erwin Chargaff stated that for double-stranded DNA, the ratios between Adenine and Thymine and Guanine and Cytosine are constant and equal to one. Thus, total purines (A+G) equal total pyrimidines (T+C).
The pitch of the DNA helix in the B-form is approximately:
- A 3.4 nm
- B 0.34 nm
- C 2.0 nm
- D 34 nm
Correct answer: 3.4 nm
The pitch (one full turn) of the B-DNA helix is 3.4 nm. There are roughly 10 base pairs in each turn, meaning the distance between consecutive base pairs is 0.34 nm.
Which bond links the 3' carbon of one sugar to the 5' carbon of the next sugar in a nucleotide chain?
- A Glycosidic bond
- B Hydrogen bond
- C Ester bond only
- D Phosphodiester bond
Correct answer: Phosphodiester bond
Nucleotides are linked together through 3'-5' phosphodiester bonds to form a long chain. This linkage involves the phosphate group reacting with the hydroxyl groups of two sugars.
The primary function of DNA in living organisms is to:
- A Act as an enzyme
- B Store and transmit genetic information
- C Provide structural support to the cell
- D Synthesize lipids
Correct answer: Store and transmit genetic information
DNA is the genetic material in the vast majority of organisms. It carries the instructions for the development, functioning, and reproduction of all known living things.
RNA is generally found in which structural form?
- A Double-stranded helical molecule
- B Single-stranded polynucleotide
- C Triple-stranded coil
- D Circular protein ring
Correct answer: Single-stranded polynucleotide
Unlike DNA, RNA is typically a single-stranded molecule. However, it can fold back on itself to form complex secondary structures through internal base pairing.
Adenine and Guanine differ from Cytosine and Thymine in that they have:
- A A single-ring structure
- B A double-ring structure
- C No nitrogen atoms
- D A phosphate attached to the ring
Correct answer: A double-ring structure
Purines (Adenine and Guanine) are larger molecules consisting of a six-membered ring fused to a five-membered ring. Pyrimidines consist of a single six-membered ring.
Which type of RNA brings amino acids to the ribosome during protein synthesis?
- A mRNA
- B rRNA
- C tRNA
- D snRNA
Correct answer: tRNA
Transfer RNA (tRNA) acts as an adapter molecule. It reads the code on the mRNA and brings the corresponding amino acid to the ribosome to build a polypeptide chain.
The bond between the nitrogenous base and the pentose sugar in a nucleotide is a:
- A Phosphodiester bond
- B N-glycosidic bond
- C Peptide bond
- D Hydrogen bond
Correct answer: N-glycosidic bond
A nitrogenous base is linked to the pentose sugar through an N-glycosidic linkage to form a nucleoside. This bond occurs at the 1' carbon of the sugar.
The plane of one base pair stacks over the other in the double helix. This provides:
- A Mutagenic properties
- B Stability to the helical structure
- C Greater flexibility for helical bending
- D Color to the DNA
Correct answer: Stability to the helical structure
In addition to hydrogen bonding, the stacking of base pairs provides stability to the DNA double helix through van der Waals forces and hydrophobic interactions.
DNA is considered 'acidic' in nature because of the presence of:
- A Nitrogenous bases
- B Pentose sugars
- C Phosphate groups
- D Histone proteins
Correct answer: Phosphate groups
The phosphate groups in the backbone of DNA are derived from phosphoric acid and carry negative charges. This gives DNA an overall acidic character and a negative charge.
Nucleic acids are also known as 'polynucleotides' because they are:
- A Long chains of simple sugars
- B Long polymers of nucleotides
- C Made of many nuclei
- D Attached to many proteins
Correct answer: Long polymers of nucleotides
Nucleic acids are high-molecular-weight macromolecules formed by the polymerization of thousands or millions of nucleotide monomers, earning them the name polynucleotides.