Final answer:
Transcription begins at the promoter, a specific DNA sequence where transcription machinery binds to initiate the process. This sequence includes special regions like the TATA box in prokaryotes and can involve additional regulatory sequences like the CAAT and GC boxes in eukaryotes. Option a.
Step-by-step explanation:
Transcription starts near a site in DNA known as the promoter. This is the specific sequence of DNA to which the transcription machinery, including RNA polymerase and various transcription factors, binds in order to initiate transcription.
The promoter is typically located upstream of the gene it regulates. Within the promoter, there are regions that are conserved among prokaryotic species, such as the -10 and -35 regions.
In bacteria, the -10 region is known as the TATA box, with the consensus sequence TATAAT, while the -35 sequence is TTGACA and is bound by the sigma subunit of RNA polymerase. This binding is crucial for the polymerase to properly initiate transcription of the gene.
In eukaryotes, promoters are larger and more complex, including additional elements like the CAAT box and the GC box, which can be bound by specific transcription factors to regulate gene transcription.
Transcription factors that bind to these elements near the promoter influence the transcription of the gene through a regulatory mechanism known as cis-acting elements.
SO Option a is correct.