Transcription

Question 1

The 3 stages of transcription

Answer 1

• Initiation: Enzyme recognises + binds to the promoter + melts DNA
• Elongation: Enzyme moves along the template during elongation + synthesis RNA
• Termination: The enzyme dissociates at termination + releases RNA

Question 2

Difference between bacterial and eukaryotic RNAP

Answer 2

• Bacteria typically have 1 RNAP that catalyses the synthesis of all classes of bacterial RNA, eukaryotes have multiple types of nuclear RNAP, each responsible for synthesis of a distinct subset of RNA
• All are structurally + mechanistically related to each other + to bacterial RNAP

Question 3

Transcription Initiation (Bacterial)

Answer 3

• Eukaryotic RNAP cannot recognise DNA without accessory proteins
• One of the most extensively regulated steps in gene expression
• Steps:
  + Promoter search
  + Closed complex
  + Open complex
  + Abortive initiation
  + Promoter escape

Question 4

Promoter-Polymerase Complex stage

Answer 4

• Before elongation, DNA is in the form of a double helix at the front end of RNAP where it enters the groove on the leading edge
• Holoenzyme + promoter (DNA is still within duplex) is called the closed binary complex
• As the ds’ed region reaches the active site (identified bu Mg2+ ion), it unwinds to a ss’ed form creating a bubble called open-binary complex

Question 5

Ternary complex

Answer 5

• Comprised of RNAP + DNA + 1st 2 nucleotides in RNA product

Question 6

Transcription Elongation (Bacterial)

Answer 6

• The elongation of the newly synthesised RNA strand with the addition of new nucleotides
• Certain DNA sequences/structures + other blockages of elongation can stall the process ie DNA damage

Question 7

Transcription Termination (Bacterial)

Answer 7

• The DNA sequences required for termination are located upstream of the terminator sequence
• Bacteria have 2 types of terminators that have been identified:
  + Intrinsic terminators includes palindromic regions that forms hairpins varying in length from 7-20bp
• Transcription terminates when inverted repeats of a hairpin is followed by a string of uracils
  + Rho factor dependent terminators