Question

Propose an explanation for why RNA polymerase is not bound to the promoter in diagram A of model 3.

Answer 1

A lack of RNA polymerase binding to the promoter may be due to the absence of necessary transcription factors such as general transcription factors or sigma factors. Additionally, specific observations that indicate a defect in RNA polymerase I include reduced transcription of ribosomal RNA, nucleolar disorganization, and unaffected mRNA and tRNA levels.

Step-by-step explanation:

The question asks for an explanation for why RNA polymerase is not bound to the promoter in a given diagram. A potential reason RNA polymerase is not bound to the promoter may be because certain transcription factors or sigma factors necessary for binding have not yet associated with the polymerase. In eukaryotes, RNA polymerase II requires general transcription factors to initiate transcription, while in prokaryotes, a sigma factor is often required for RNA polymerase to recognize the promoter.

To support the conclusion that a defect in RNA polymerase I activity specifically causes a protein synthesis deficiency observed in a cell, one could look for:

1. Reduced transcription of ribosomal RNA, which is synthesized by RNA polymerase I.
2. Nucleolar disorganization, since RNA polymerase I activity is associated with nucleolar integrity.
3. Normal levels of mRNA and tRNA, as these are synthesized by RNA polymerases II and III, respectively, and should not be affected by a failure in RNA polymerase I activity.