Answer: (a) The statement that RNA Polymerase II in E. coli engages in a "one-dimensional search for promoters" means that the polymerase molecule moves along the DNA strand in a linear, sequential manner, scanning the DNA for specific promoter sequences that indicate the start of a gene. This process is called a "one-dimensional search".
(b) An alternative to the one-dimensional search would be a "three-dimensional search," where the polymerase could potentially jump between different DNA strands or traverse through the 3D space to locate promoters more efficiently. The sigma factor plays a crucial role in promoter identification and in transcription in bacteria like E. coli.
(c) The sigma factor plays a crucial role in promoter identification and in transcription in bacteria like E. coli.
Explanation: "The sigma factor plays a crucial role in promoter identification and in transcription in bacteria like E. coli:
Promoter Identification: The sigma factor is a subunit of bacterial RNA polymerase. It helps recognize and bind to specific DNA sequences known as promoter regions. Promoters are crucial because they indicate where transcription should initiate. The sigma factor facilitates the recognition of promoter sequences, enabling RNA polymerase to bind at the correct site on the DNA.
Transcription Initiation: Once the sigma factor guides RNA polymerase to the promoter site, the polymerase initiates transcription by unwinding the DNA and synthesizing an RNA strand complementary to the template DNA strand. The sigma factor helps stabilize the initial binding of RNA polymerase to the promoter and assists in the formation of the transcription initiation complex."