Final answer:
During 'binding and initiation' of transcription, DNA unwinds, and transcription factors and RNA polymerase bind to the promoter, forming a complex that begins RNA synthesis.
Step-by-step explanation:
Binding and Initiation of Transcription
Drawing upon the given references, during the 'binding and initiation' phase of transcription, several critical steps occur to begin the process of synthesizing RNA from DNA. Firstly, the DNA unwinds at the region where transcription will start, which is characterized by a promoter—a specific sequence of DNA nucleotides. Transcription factors then bind to this promoter, significantly affecting whether the corresponding gene is transcribed frequently or seldom.
The enzyme responsible for synthesizing RNA, called the RNA polymerase, subsequently binds to the promoter's sequence, forming the 'closed complex.' This step is crucial for initializing transcription. Next, the DNA is unwound further leading to the creation of an 'open complex', allowing RNA polymerase to start synthesizing RNA by adding complementary RNA nucleotides to the growing RNA strand using the antisense strand of DNA as a template.
In bacteria, the σ (sigma) subunit of the RNA polymerase plays a critical role in initiation by enabling the polymerase to recognize the promoter sequences. Once the initiation complex, comprised of the RNA polymerase and transcription factors, is bound to the promoter, transcription can begin in earnest.