Question

For each question, please explain how you got the answer.

1. The major function of RNA polymerase's sigma factor is
A) recognition of the translational stop sequence
B) recognition of the transcriptional start sequence
C) recognition of the transcriptional stop sequence
D) recognition of the translational start sequence
E) None of these are correct

2. WHere is the amino acid attached to a tRNA molecule?

A) 3′-hydroxyl of an adenine containing residue of 3’ end of tRNA
B) 5′-hydroxyl of a uridine containing residue of 3’ end of tRNA
C) 5′-hydroxyl of a guanine containing residue of 3’ end of tRNA
D) 3′-hydroxyl of a cytosine containing residue of 3’ end of tRNA
E) 2′-hydroxyl of a guanine containing residue of 3’ end of tRNA

3. Functions of RNA polymerase in E. Coli include
A) searching for promoter sites.
B) unwinding short stretches of DNA.
C) detecting termination signals.
D) searching for promoter sites and detecting termination signals.
E) All the answers are correct.

4. Actinomycin D inhibits transcription by:
A) binding to the DNA template by intercalation
B) binding to the RNA polymerase
C) binding to rho protein
D) Binding to the sigma subunit
E) none of the above

Answer 1

​​​​1. Explanation- The major function of RNA polymerase's Sigma factor is to initiate transcription and also direct the binding of RNA polymerase to promoter site. The protein sigma factor is needed in the bacteria for the initiation of transcription. The Sigma factor helps in the binding of RNA polymerase to the promoter site to start transcription. The sigma factor with the RNA polymerase together knows as RNA polymerase holoenzyme. Selection of the promoter site is dependent on sigma factor associated with RNA polymerase.

Thus, the correct option is B. Recognition of the transcriptional start sequence

2. The correct option is A 3'-hydroxyl of an Adenine containing residue of 3' end of tRNA.

Explaination- The tRNA has CCA ( cytosine-cytosine-adenine) tail where 3' hydroxyl group of Adenine attach to the 3' end of tRNA. The amino acid attaches to the 3' end of tRNA, this attachment is catalyses by the enzyme called aminoacyl tRNA synthetase. The aminoacyl-tRNA bonded covalently to 3'-hydroxyl group on CCA tail ( the cytosine-cytosine-adenine sequence in the 3' end of tRNA).

3. The correct option is E. All the answers are correct.

Explaination- RNA polymerase searches for the promoter sites in DNA sequence to start the transcription. RNA polymerase also known as RNAP. The RNAP releases some transcripts in the DNA for detecting the termination signals. The RNAP undwinds the DNA for the purpose of transcription.

4. The correct option is  A. Binding to the DNA template by intercalation.

​​​​​​Explaination- The actinomycin D is an antibiotic which is used to inhibit transcription. Actinomycin D done this by binding at the initiation of transcription of DNA and stop the elongation of RNA by RNA polymerase. Actinomycin D by damaging the DNA inhibit the transcription. The actinomycin D antibiotics are used to kill cancer cells.