Topic 2 Molecular Genetics: Transcription

Question 1

• Transcription serves to create RNA molecules from a DNA template in the nucleus. This process has three main steps

Answer 1

Note

Question 2

• RNA polymerase attaches to the promoter region on DNA and unzips the DNA into two strands. A promoter region for mRNA transcription often contains a repeating sequence of A and T nucleotides called the TATA box.
• The most common sequence of nucleotides at the promoter region is called the consensus sequence - variations from it cause less tight RNA polymerase binding, and therefore a lower transcription rate
• Note that the promoter is the site on DNA where RNA polymerase binds to initiate transcription, but it is not the start site; it’s actually just upstream of the start site!

Answer 2

1. Initiation

Question 3

• The TATA box is in eukaryotes, while in prokaryotes, it is termed the ‘Pribnow box’ (think P for P, Prokaryote Pribnow)

Answer 3

Note

Question 4

• RNA polymerase continues unzipping DNA and assembles RNA nucleotides using one strand of DNA as a template. Only one strand is transcribed, from the template = (-) antisense strand, while the other strand is the coding (+) sense strand for protection against degradation

Answer 4

2. Elongation

Question 5

• occurs when RNA polymerase reaches a special sequence, often AAAAAA in eukaryotes

Answer 5

3. Termination

Question 6

• Transcription is occurring in the 3’ to 5’ direction of the DNA template strand (but synthesis of the RNA strand is, as always, 5’ to 3’)
• Note that RNA polymerase doesn’t have proofreading ability, therefore RNA synthesis has a much greater error level than that of DNA synthesis

Answer 6

Note