Chapter 14, Problem 1TYU

In eukaryotic cells, transcription cannot begin until

1. A.    the two DNA strands have completely separated and exposed the promoter.
2. B.     several transcription factors have bound to the promoter.
3. C.     the 5’ caps are removed from the mRNA.
4. D.    the DNA introns are removed from the template.

Summary Introduction

Introduction:

DNA (deoxyribonucleic acid) consists of genetic instructions that are necessary for the development and functioning of living cells and it can be transmitted from parents to offspring. Transcription is the process that involves the synthesis of RNA (ribonucleic acid) from DNA.

Answer to Problem 1TYU

Correct answer:

In eukaryotic cells, transcription cannot begin until several transcription factors have bound to the promoter. Therefore, option (B) is correct.

Explanation of Solution

Reason for the correct statement:

There are certain differences between prokaryotic transcription and eukaryotic transcription. In the case of prokaryotic transcription, the transcription can begin without the involvement of transcriptional factors. However, in eukaryotic transcription, the transcription is initiated only when several transcription factors bind to it. These transcription factors get dissociated once the transcription is initiated.

Option (B) is given as “several transcription factors have bound to the promoter”.

“The transcription cannot begin until transcription factors have bound to the promoter in eukaryotic cells” is the right answer.

Hence, option (B) is correct.

Reasons for the incorrect statements:

Option (A) is given as “the two DNA strands have completely separated and exposed the promoter”.

In transcription, the double-stranded DNA will separate only after the binding of RNA polymerase to the promoter region. RNA polymerase will attach to DNA only in the presence of transcriptional factors. Therefore, option (A) is the wrong answer.

Option (C) is given as “the 5' caps are removed from the $\text{mRNA}$”.

The $\text{mRNA}$ (messenger RNA) is the final product of transcription. Thus, the removal of 5’ caps from the $\text{mRNA}$ does not initiate transcription. Therefore, option (C) is the wrong answer.

Option (D) is given as “the DNA introns are removed from the template”.

The introns are the non-coding nucleotide sequences, which are spliced before the formation of the final product of mRNA. The transcription process does not require the removal of introns from the template for the initiation of the process. Therefore, option (D) is the wrong answer.

Hence, options (A), (C), and (D) are incorrect.

Conclusion

Transcription cannot begin until the transcription factors have bound to the promoter in the eukaryotic cells.