MCQ Bank

RNA polymerase incorporates ribonucleotides (rNTPs) at a much lower rate than deoxyribonucleotides (dNTPs) in DNA synthesis contexts. The incorporation rate is approximately 1000-fold lower.

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____________polymerase can initiate a new RNA chain on a DNA template

A) DNA
B) RNA
C)
D)

AI Explanation

RNA polymerase can initiate a new RNA chain directly on a DNA template without requiring a pre-existing primer. This distinguishes RNA polymerase from DNA polymerase, which generally requires a primer.

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There are three human MutS homologs

A) MSH2, MSH3, MSH6
B)
C)
D)

AI Explanation

Humans have three major MutS homologs involved in mismatch repair: MSH2, MSH3, and MSH6. MSH2 forms heterodimers with MSH3 or MSH6 to recognize different types of DNA mismatches.

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____________ nucleotide or nucleoside can be accommodated by group I binding pocket.

A) Adenine
B) Thymine
C) Guanine
D) Uracil

AI Explanation

The group I binding pocket of RNA polymerase accommodates nucleotides or nucleosides containing uracil. Uracil is a pyrimidine base commonly found in RNA.

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Which enzyme prevents the accumulation of supercoils ahead of the replication fork?

A) helicase
B)
C)
D)

AI Explanation

Helicase unwinds the DNA double helix at the replication fork, but it does not prevent supercoil accumulation. The enzyme that actually relieves supercoiling is DNA gyrase/topoisomerase; however, among the given options, helicase is the only listed enzyme.

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Due to presence of introns ________ type of RNA is first generated from DNa

A) Mature mRNA
B) miRNa
C) mRNA
D) Pre mRNa

AI Explanation

Because eukaryotic genes contain introns, transcription initially produces a precursor mRNA (pre-mRNA). Introns are subsequently removed by RNA splicing to generate mature mRNA.

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Hydrolytic deamination of cytosine is estimated to take place about a.... times a day in a mammalian cell

A) 100 to 500
B)
C)
D)

AI Explanation

Hydrolytic deamination of cytosine is a spontaneous DNA-damaging reaction that occurs frequently in mammalian cells. Estimates place the number of such events at roughly 100 to 500 per cell per day.

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Pol I is required for the expression of only one gene, that encoding the_____________precursor

A) rRNA
B) All given
C) mRNA
D) tRNA

AI Explanation

RNA polymerase I is primarily responsible for transcribing the large precursor rRNA in eukaryotic cells. This precursor is processed to produce the major ribosomal RNAs.

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Which of the following is not a base of RNA?

A) Thymine(T)
B)
C)
D)

AI Explanation

RNA normally contains adenine, guanine, cytosine, and uracil. Thymine is primarily a DNA base and is not normally found as a standard RNA base.

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TFIIB protein is a __________polypeptide chain, enters the preinitiation complex

A) double
B) single
C)
D)

AI Explanation

TFIIB is a single polypeptide chain that enters the RNA polymerase II preinitiation complex. It helps position RNA polymerase II correctly at the promoter and contributes to transcription initiation.

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Psoralen can DNA if photo-activated.

A) Alkylate
B)
C)
D)

AI Explanation

Psoralen molecules intercalate into DNA and, upon activation by ultraviolet light, form covalent bonds with pyrimidine bases. This process effectively alkylates DNA and can produce DNA cross-links.

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Q10

The internal guide sequence of group I introns base pairs with ______________.

A) 3’ splice site sequence
B) 5’ and 3’ site
C) 5’ splice site sequence
D) No specific site

AI Explanation

The internal guide sequence (IGS) of group I introns base-pairs with the 5′ splice-site region. This interaction helps position the splice junction correctly for the first transesterification reaction.

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Q10

The bond angles in protein primary structure resulting from rotations at C are labelled (phi) for the

A) N-alpha C
B)
C)
D)

AI Explanation

The phi (φ) angle in a polypeptide backbone describes rotation around the N–Cα bond. In contrast, the psi (ψ) angle describes rotation around the Cα–C bond.

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Q11

A gene coding sequence is a series of __________ nucleotide codons.

A) 2
B) 3
C) 4
D) 5

AI Explanation

A gene coding sequence is read as a series of three-nucleotide codons. Each codon specifies an amino acid or a stop signal during translation.

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Q11

Meselson and Stahl performed a classical experiment to distinguish among three possible models of DNA replication using isotope of

A) N
B)
C)
D)

AI Explanation

Meselson and Stahl used nitrogen isotopes, specifically 14N and 15N, to distinguish conservative, semiconservative, and dispersive DNA replication. The DNA was separated by density using cesium chloride centrifugation.

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Q12

phosphorylation of the CTD leads to an exchange of initiation factors for those factors required for______________

A) termination
B) elongation
C)
D)

AI Explanation

Phosphorylation of the C-terminal domain (CTD) of RNA polymerase II promotes the transition from transcription initiation to elongation. It facilitates the exchange of initiation factors for factors needed during elongation.

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Q12

DNA polymerases introduce about one mis-paired nucleotide per nucleotides.

A) 10^5
B)
C)
D)

AI Explanation

DNA polymerases have high fidelity and initially introduce approximately one mispaired nucleotide per 10^5 nucleotides incorporated. Proofreading and mismatch repair further reduce the final mutation rate.

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Q13

Find the wrong statement in the following:

A) Primary transcripts of intron-containing genes must have their introns removed before they can be translated into proteins.
B) Once transcribed into an RNA transcript, the introns must be removed
C) Introns are very often much longer than the exons they separate
D) The primary transcript only contains exons

AI Explanation

This statement is incorrect because the primary transcript of an intron-containing gene contains both exons and introns. Introns are removed during RNA splicing before the mature mRNA is translated.

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Q13

Overall three dimensional arrangement of all atoms in protein

A) Tertiary structure of protein
B)
C)
D)

AI Explanation

The tertiary structure is the overall three-dimensional arrangement of all atoms in a single polypeptide chain. It results from interactions among amino acid side chains and the backbone.

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Q14

During RNA splicing pre-mRNA is converted into mature mRNA containing __________.

A) Exons
B) 3 codons
C) Introns and Exons
D) Introns

AI Explanation

During RNA splicing, introns are removed and the remaining exons are joined together. The resulting mature mRNA therefore contains the joined exon sequences.