Question

How does the rna polymerase know which genes to bind to?

Answer 1

RNA polymerase binds to DNA at specific promoter sequences, with the aid of transcription factors that enhance or repress its activity. In prokaryotes, the sigma factor is crucial for promoter recognition. Termination signals in the DNA sequence signal the RNA polymerase to stop transcribing.

Step-by-step explanation:

RNA polymerase recognizes and binds to specific regions on DNA called promoter sequences to initiate transcription. These promoters contain distinct sequences such as the TATA box, GC box, and CAT box in eukaryotes, or the Pribnow box in prokaryotes, and are recognized by transcription factors. Transcription factors play a crucial role by binding to these sequences and enhance or repress the binding of RNA polymerase to DNA. An essential factor in prokaryotes is the sigma (σ) factor, which helps the RNA polymerase to bind to promoters and start transcription.

Once bound, RNA polymerase unwinds the DNA forming a transcription bubble, allowing the synthesis of RNA. Transcription continues until a termination signal is encountered, such as a rho-dependent termination sequence in prokaryotes. The specific binding of transcription factors and accessory proteins determines which genes are transcribed, ensuring that cells can differentially express genes according to their functions and needs.

Answer 2

In DNA, there are certain specific sequences that the RNA polymerase recognizes as the signal that they are to bind at that point and start transcription: promoters. A promoter usually has three parts: the DNA "start site," the "-10 sequence" that appears before the start site, and the "-35 sequence" that appears before the -10 sequence. The coding at the -35 sequence is TTGACA. One can consider these two pre-sites as a notice to watch for the start site, where the actual binding occurs.