Nucleic Acids Practice Questions
38 free Nucleic Acids practice questions for the Zoology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Nucleic acids are polymers composed of repeating units called:
- A Amino acids
- B Nucleotides
- C Fatty acids
- D Monosaccharides
Correct answer: Nucleotides
Nucleic acids are made up of nucleotide monomers. Each nucleotide consists of a nitrogenous base, a pentose sugar, and a phosphate group.
Which sugar is present in DNA?
- A Ribose (a pentose sugar)
- B Deoxyribose
- C Glucose (a hexose sugar)
- D Fructose (a ketohexose)
Correct answer: Deoxyribose
DNA contains 2'-deoxyribose, a five-carbon sugar that lacks a hydroxyl group at the 2' carbon position. This single oxygen difference from ribose (found in RNA) makes the DNA backbone more chemically stable and less susceptible to hydrolysis.
The backbone of a nucleic acid strand consists of alternating:
- A Alternating sugar and base units
- B Alternating base and phosphate units
- C Alternating sugar and phosphate units
- D Consecutive base and base stacking only
Correct answer: Alternating sugar and phosphate units
The structural backbone of a nucleic acid strand consists of alternating sugar (deoxyribose in DNA, ribose in RNA) and phosphate groups linked by phosphodiester bonds. The nitrogenous bases are attached to the sugars and project inward (in the double helix) or outward from this backbone.
Which type of bond links nucleotides in a nucleic acid strand?
- A Peptide bond (amide linkage)
- B Hydrogen bond (non-covalent)
- C Phosphodiester bond
- D Glycosidic bond (sugar linkage)
Correct answer: Phosphodiester bond
Adjacent nucleotides in a nucleic acid strand are covalently joined by phosphodiester bonds: each phosphate group bridges the 3'-hydroxyl of one sugar to the 5'-carbon of the next, forming the continuous sugar-phosphate backbone. Hydrogen bonds, in contrast, hold the two strands of the double helix together through base pairing.
In DNA, adenine pairs specifically with:
- A Guanine
- B Cytosine
- C Uracil
- D Thymine
Correct answer: Thymine
Adenine forms two hydrogen bonds with thymine in DNA. This base pairing maintains the double helix structure.
Which RNA type carries amino acids to the ribosome?
- A mRNA
- B rRNA
- C tRNA
- D snRNA
Correct answer: tRNA
Transfer RNA transports specific amino acids to the ribosome during protein synthesis. Each tRNA recognizes a codon on mRNA.
Messenger RNA functions primarily to:
- A Structurally build ribosomes alongside rRNA
- B Carry genetic code from DNA to ribosomes
- C Shuttle amino acids to the ribosome
- D Regulate gene expression at the chromatin level
Correct answer: Carry genetic code from DNA to ribosomes
mRNA carries the genetic information transcribed from DNA to ribosomes, where it serves as the template for protein synthesis.
Ribosomal RNA is mainly involved in:
- A DNA transcription
- B DNA strand replication
- C Protein synthesis
- D mRNA splicing reactions
Correct answer: Protein synthesis
rRNA forms the structural and catalytic core of ribosomes and plays a central role in protein synthesis, coordinating the interaction between mRNA codons and tRNA anticodons.
Which property distinguishes DNA from RNA?
- A Presence of phosphate groups
- B Presence of nitrogenous bases
- C Double-stranded structure
- D Polymeric nature
Correct answer: Double-stranded structure
DNA is usually double-stranded, while RNA is typically single-stranded. This structural difference affects their stability and function.
Chargaff's rule states that in DNA:
- A Adenine equals Thymine and Guanine equals Cytosine
- B Adenine equals Guanine and Thymine equals Cytosine
- C Purines always equal pyrimidines in RNA only
- D DNA is inherently single-stranded in cells
Correct answer: Adenine equals Thymine and Guanine equals Cytosine
Chargaff's rules state that in DNA, adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C), so their quantities are always equal. This complementary base pairing supports the double-helix model.
Which base pairing occurs in RNA?
- A A–T
- B G–T
- C A–U
- D C–U
Correct answer: A–U
In RNA, adenine pairs with uracil. Thymine is absent in RNA.
The directionality of a nucleic acid strand is described as:
- A Amino to carboxyl end
- B 5' to 3' direction
- C N-term to C-term
- D Alpha to omega end
Correct answer: 5' to 3' direction
Nucleic acid strands have a 5' to 3' directionality based on the orientation of the sugar-phosphate backbone. This polarity is essential for replication, transcription, and translation.
Which RNA molecule is involved in post-transcriptional modification?
- A Messenger RNA (mRNA)
- B Transfer RNA (tRNA)
- C Small nuclear RNA (snRNA)
- D Ribosomal RNA (rRNA)
Correct answer: Small nuclear RNA (snRNA)
Small nuclear RNA (snRNA) is found in the nucleus and is a core component of spliceosomes, which remove introns from pre-mRNA during post-transcriptional modification.
Which nucleotide base is a purine?
- A Cytosine
- B Thymine
- C Uracil
- D Adenine
Correct answer: Adenine
Adenine is a purine with a double-ring structure. Purines include adenine and guanine.
RNA differs from DNA in being more:
- A Structurally stable over time
- B Strongly hydrophobic in nature
- C Chemically reactive
- D Predominantly double-stranded
Correct answer: Chemically reactive
RNA is more chemically reactive than DNA due to the 2'-hydroxyl group on its ribose sugar, which makes it susceptible to hydrolysis. This also makes RNA less stable than DNA.
Which nucleic acid carries hereditary information in most organisms?
- A Ribonucleic acid (RNA)
- B Deoxyribonucleic acid (DNA)
- C Structural protein complexes
- D Complex polysaccharide chains
Correct answer: Deoxyribonucleic acid (DNA)
DNA (deoxyribonucleic acid) stores and transmits hereditary information in most organisms. Its stable double-stranded structure and proofreading mechanisms ensure accurate transmission of genetic traits during cell division.
Which form of DNA is commonly found in cells?
- A A-DNA
- B B-DNA
- C Z-DNA
- D C-DNA
Correct answer: B-DNA
B-DNA is the most common and stable form of DNA under physiological conditions. It has a right-handed double helix.
The primary function of nucleic acids is to:
- A Store and transmit genetic information
- B Supply chemical energy to cells
- C Provide structural support to membranes
- D Catalyze cellular metabolic reactions
Correct answer: Store and transmit genetic information
The primary function of nucleic acids (DNA and RNA) is to store and transmit genetic information. They control cellular function by directing protein synthesis through transcription and translation.
According to Chargaff's rules, if a double-stranded DNA molecule contains 30% Adenine, what is the percentage of Cytosine present?
- A 20%
- B 30%
- C 40%
- D 70%
Correct answer: 20%
If A=30%, then T=30% (Total 60%). The remaining 40% must be shared equally between G and C, making C=20%.
Which specific chemical group is attached to the 5' carbon of the pentose sugar in a nucleotide?
- A Hydroxyl group
- B Nitrogenous base
- C Phosphate group
- D Carboxyl group
Correct answer: Phosphate group
Nucleotides consist of a sugar, a base, and a phosphate group. The phosphate is esterified to the 5' carbon, while the base is attached to the 1' carbon.
Which of the following nitrogenous bases is a pyrimidine found exclusively in RNA?
- A Thymine
- B Uracil
- C Adenine
- D Guanine
Correct answer: Uracil
Uracil is a pyrimidine that replaces Thymine in RNA. Adenine and Guanine are purines found in both DNA and RNA.
The phosphodiester bond that links two nucleotides in a DNA strand is formed between:
- A The 1' carbon of one sugar and the 5' carbon of the next nucleotide
- B The 3' OH group of one sugar and the 5' phosphate of the next
- C The nitrogenous bases found on opposing strands
- D Two separate phosphate groups at the 5' end
Correct answer: The 3' OH group of one sugar and the 5' phosphate of the next
DNA polymerization occurs in the 5' to 3' direction, where the phosphate at the 5' position of a new nucleotide reacts with the 3'-OH group of the existing chain.
Which form of DNA is a left-handed helix with a 'zigzag' sugar-phosphate backbone?
- A A-DNA
- B B-DNA
- C Z-DNA
- D C-DNA
Correct answer: Z-DNA
Z-DNA is a rare, left-handed double helix. A-DNA and B-DNA are right-handed, with B-DNA being the most common biological form.
The 'cloverleaf' secondary structure is a characteristic feature of which type of RNA?
- A mRNA
- B rRNA
- C tRNA
- D snRNA
Correct answer: tRNA
Transfer RNA (tRNA) folds into a cloverleaf shape due to internal base pairing, which is essential for its role in carrying amino acids to the ribosome.
Which of the following is the primary reason why RNA is more chemically unstable and susceptible to hydrolysis than DNA?
- A The presence of Uracil in place of Thymine
- B It usually exists as a single-stranded molecule
- C It lacks a stable phosphate backbone structure
- D A hydroxyl group at the 2' position of ribose
Correct answer: A hydroxyl group at the 2' position of ribose
The 2'-OH group in ribose makes RNA more chemically reactive and prone to alkaline hydrolysis compared to 2'-deoxyribose in DNA.
In the DNA double helix, how many hydrogen bonds form between Guanine and Cytosine?
- A 1
- B 2
- C 4
- D 3
Correct answer: 3
G-C pairs are held together by three hydrogen bonds, while A-T pairs are held together by two, making G-C rich regions more stable.
What is the primary function of small nuclear RNA (snRNA)?
- A Catalyzing peptide bond formation
- B Carrying genetic code to the cytoplasm
- C Regulating gene expression by RNA interference
- D Processing of pre-mRNA (splicing)
Correct answer: Processing of pre-mRNA (splicing)
snRNAs combine with proteins to form snRNPs, which are the core components of the spliceosome responsible for removing introns from pre-mRNA.
A nucleoside differs from a nucleotide because it lacks which of the following components?
- A Pentose sugar
- B Nitrogenous base
- C Hydrogen bonds
- D Phosphate group
Correct answer: Phosphate group
A nucleoside is composed only of a nitrogenous base and a sugar. Adding a phosphate group converts it into a nucleotide.
Which of the following enzymes is responsible for synthesizing a DNA strand from an RNA template in certain viruses?
- A DNA Polymerase enzyme
- B RNA Polymerase enzyme
- C Primase enzyme complex
- D Reverse Transcriptase
Correct answer: Reverse Transcriptase
Reverse transcriptase is used by retroviruses to convert their RNA genome into DNA so it can be integrated into the host cell's genome.
The melting temperature (Tm) of DNA increases as the content of which base pair increases?
- A G-C
- B A-T
- C A-U
- D G-U
Correct answer: G-C
Because G-C pairs have three hydrogen bonds compared to the two in A-T pairs, more energy (heat) is required to separate strands with higher G-C content.
Which RNA molecule possesses catalytic activity and can function like an enzyme?
- A Ribozyme
- B Messenger RNA
- C Transfer RNA
- D Silencer RNA
Correct answer: Ribozyme
Ribozymes are RNA molecules capable of acting as biological catalysts, such as the rRNA that catalyzes peptide bond formation in the ribosome.
DNA strands are described as 'antiparallel'. This means:
- A One strand runs 5' to 3' and the other runs 3' to 5'
- B They physically rotate in opposite directions
- C They have entirely different nitrogenous bases
- D They cannot be copied or replicated at the same time
Correct answer: One strand runs 5' to 3' and the other runs 3' to 5'
Antiparallel orientation means the two strands of the double helix have opposite chemical polarity, which is essential for base pairing and replication.
Which type of RNA makes up the largest percentage of total RNA within a typical eukaryotic cell?
- A mRNA
- B tRNA
- C miRNA
- D rRNA
Correct answer: rRNA
Ribosomal RNA (rRNA) accounts for about 80% of the total RNA in a cell because ribosomes are present in vast numbers for protein synthesis.
What is the effect of 'Hyperchromicity' in nucleic acids?
- A UV light absorbance increases when DNA is denatured
- B DNA appears to become more colorful under a microscope
- C The DNA molecule shrinks and becomes more compact
- D RNA begins to bind more tightly to the DNA strand
Correct answer: UV light absorbance increases when DNA is denatured
Hyperchromicity is the increase in UV light absorption (at 260 nm) that occurs when double-stranded DNA is denatured into single strands.
Which nitrogenous bases are classified as double-ringed Purines?
- A Adenine and Guanine
- B Cytosine and Thymine
- C Adenine and Uracil
- D Guanine and Cytosine
Correct answer: Adenine and Guanine
Adenine (A) and Guanine (G) are purines, characterized by a six-membered ring fused to a five-membered ring.
In a DNA molecule, the distance between two adjacent base pairs is approximately:
- A 0.34 nm
- B 3.4 nm
- C 2.0 nm
- D 0.20 nm
Correct answer: 0.34 nm
In B-DNA, the rise per base pair is 0.34 nm, with a full turn of 10 base pairs measuring 3.4 nm.
Which of the following is found at the 3' end of a mature eukaryotic mRNA molecule?
- A 7-methylguanosine cap
- B Poly-A tail
- C Promoter sequence
- D Start codon
Correct answer: Poly-A tail
Eukaryotic mRNA is modified with a 5' cap and a 3' poly-A tail (a string of adenine nucleotides) to increase stability and facilitate translation.
The 'Hoogsteen' base pairing is occasionally found in:
- A Standard B-DNA
- B Triple-stranded DNA (Triplex)
- C mRNA-tRNA interactions
- D The primary structure of proteins
Correct answer: Triple-stranded DNA (Triplex)
Hoogsteen pairing is an alternative form of base pairing that allows a third strand to bind in the major groove of a DNA double helix, forming triplex DNA.