Transcription in Prokaryotes Questions and Answers

Q: Polycistronic transcription units are common in :

Polycistronic transcription units are common in both Archaea and Bacteria (spelt Archae in the paper).Prokaryotes group genes into operons, transcribed from one promoter into a single mRNA that carries several coding sequences, each with its own ribosome-binding site. This is standard in bacteria (the lac operon) and equally common in archaea, whose genes are also organised into operons.Eukaryotes generally transcribe each gene separately into a monocistronic mRNA, with rare exceptions such as trypanosomes and nematodes. So 'Eukarya' is wrong, and options naming only one prokaryotic domain are incomplete.

Q: Which component of prokaryotic RNA polymerase facilitates the recognition of promoter sequences ?

Promoter recognition depends on the σ subunit.Bacterial RNA polymerase holoenzyme is the core enzyme (two α, β, β' and ω) plus a sigma factor. The sigma factor recognises the -35 and -10 promoter sequences and positions the polymerase to start transcription; after initiation it is released. Different sigma factors, such as σ70 and σ32, direct the enzyme to different sets of genes.The α subunits assemble the core and contact some regulators, β carries the catalytic site, and there is no λ subunit of RNA polymerase.

Q: Which of the following sigma subunit of prokaryotic RNA Polymerase is responsible for transcription of housekeeping genes ?

Housekeeping genes are transcribed with Sigma 70.In E. coli, sigma 70 (RpoD) is the primary sigma factor. It directs RNA polymerase holoenzyme to promoters with the -35 (TTGACA) and -10 (TATAAT) consensus sequences, which drive most genes needed for normal growth.The others are alternative sigma factors used for special programmes. Sigma 32 (RpoH) transcribes heat shock genes. Sigma 54 (RpoN) recognises -24/-12 promoters, for example for nitrogen-assimilation genes, and needs an activator protein. Sigma 28 (FliA) transcribes flagellar and chemotaxis genes.

Q: What will be the possible RNA sequence from complete transcription of a DNA molecule with the sequence in one of the strand is 5' - AGCTGCAATG -3' ?

The transcript is 5' - AGCUGCAAUG -3'.Taking the given strand as the coding (sense) strand, the RNA is copied from the complementary template strand and so has the same sequence and the same 5' to 3' direction as the coding strand, with uracil in place of thymine: AGCTGCAATG becomes AGCUGCAAUG.Options containing T are DNA, not RNA, and one of them gives 5' at both ends, which is impossible. The remaining option, UCGACCUUAC, is neither the coding sequence nor the correct antiparallel complement of either strand.

Polycistronic transcription units are common in :

A.Archae
B.Bacteria
C.Eukarya
D.Both Archae and Bacteria

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: D

Polycistronic transcription units are common in both Archaea and Bacteria (spelt Archae in the paper).

Prokaryotes group genes into operons, transcribed from one promoter into a single mRNA that carries several coding sequences, each with its own ribosome-binding site. This is standard in bacteria (the lac operon) and equally common in archaea, whose genes are also organised into operons.

Eukaryotes generally transcribe each gene separately into a monocistronic mRNA, with rare exceptions such as trypanosomes and nematodes. So 'Eukarya' is wrong, and options naming only one prokaryotic domain are incomplete.

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Which component of prokaryotic RNA polymerase facilitates the recognition of promoter sequences ?

A.α subunit
B.β subunit
C.σ subunit
D.λ subunit

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: C

Promoter recognition depends on the σ subunit.

Bacterial RNA polymerase holoenzyme is the core enzyme (two α, β, β' and ω) plus a sigma factor. The sigma factor recognises the -35 and -10 promoter sequences and positions the polymerase to start transcription; after initiation it is released. Different sigma factors, such as σ⁷⁰ and σ³², direct the enzyme to different sets of genes.

The α subunits assemble the core and contact some regulators, β carries the catalytic site, and there is no λ subunit of RNA polymerase.

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Which of the following sigma subunit of prokaryotic RNA Polymerase is responsible for transcription of housekeeping genes ?

A.Sigma 32
B.Sigma 54
C.Sigma 70
D.Sigma 28

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: C

Housekeeping genes are transcribed with Sigma 70.

In E. coli, sigma 70 (RpoD) is the primary sigma factor. It directs RNA polymerase holoenzyme to promoters with the -35 (TTGACA) and -10 (TATAAT) consensus sequences, which drive most genes needed for normal growth.

The others are alternative sigma factors used for special programmes. Sigma 32 (RpoH) transcribes heat shock genes. Sigma 54 (RpoN) recognises -24/-12 promoters, for example for nitrogen-assimilation genes, and needs an activator protein. Sigma 28 (FliA) transcribes flagellar and chemotaxis genes.

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What will be the possible RNA sequence from complete transcription of a DNA molecule with the sequence in one of the strand is 5' - AGCTGCAATG -3' ?

A.5' - UCGACCUUAC -3'
B.5' - AGCUGCAAUG -3'
C.5' - TCGACGTTAC -5'
D.5' - AGCTGCAATG -3'

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: B

The transcript is 5' - AGCUGCAAUG -3'.

Taking the given strand as the coding (sense) strand, the RNA is copied from the complementary template strand and so has the same sequence and the same 5' to 3' direction as the coding strand, with uracil in place of thymine: AGCTGCAATG becomes AGCUGCAAUG.

Options containing T are DNA, not RNA, and one of them gives 5' at both ends, which is impossible. The remaining option, UCGACCUUAC, is neither the coding sequence nor the correct antiparallel complement of either strand.

Discuss in Forum

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