Q17.2-2CC - Campbell Biology

Question

What enables RNA polymerase to start transcribing a gene at the right place on the DNA in a bacterial cell? In a eukaryotic cell?

Step-by-Step Solution

Answer

In the prokaryotic cell, RNA polymerase binds to the promoter segment directly and initiates the process of transcription. 

In a eukaryotic cell, transcription factors bind to the promoter region, followed by the binding of the RNA polymerase to the promoter region to initiate the transcription process.

Step 1: Description of RNA polymerase

RNA polymerase is the enzyme that synthesizes DNA from the RNA strand. It mediates the critical process in gene expression, such as transcription. 

Step 2: RNA polymerase binding in the bacterial cell

Bacteria are single-celled prokaryotic organisms. The transcription process occurs more simply in bacteria compared to eukaryotes. 

The RNA polymerase enzyme recognizes the promoter region directly and binds to it to begin the transcription process. There is no requirement for transcription factors in the prokaryotic cells. 

Step 3: RNA polymerase binding in the eukaryotic cell

Eukaryotic cells have complex organization compared to prokaryotic cells. The transcription factors are the assisting elements that facilitate the binding of the RNA polymerase with the promoter sequence. In this process, there is no direct binding involved.

The transcription factors have eligibility to control the rate of the transcription process.

Hence, the RNA polymerase itself searches for the promoters and binds to them in the case of the bacterial cell. In the eukaryotic cell, the transcription factors enable the binding of the promoter with the RNA polymerase.