Transcription

Question 1

Transcription machinery

Answer 1

• RNA is single-stranded, and built on the template DNA strand
• RNA synthesis is catalyzed by RNA polymerase II – unwinds and separates the DNA strands, and joins together the RNA nucleotides to their DNA counterpart

Question 2

Transcription factors

Answer 2

Proteins that regulate the transcription of DNA template to protein.
* Ensure that the right genes are expressed in the right cells of the body, at the right time
* RNA polymerase II can only attach to the promoter with the help of TFs
* Basal or General transcription factors
* Cell’s transcription toolkit, needed for the transcription of any gene

Question 3

Post-transcription modification (eukaryotes)

Answer 3

• Takes place in the nucleus
• Both ends are altered:
• The 5 end receives a modified nucleotide 5 cap (modified G)
• The 3 end gets a poly-A tail (50-250 Adenine bases)

Question 4

These modifications:

Answer 4

• Seem to facilitate export of mRNA from the nucleus
• Protect mRNA from hydrolytic enzymes – ‘molecular recycling’
• Help ribosomes attach to the 5’ end

Question 5

Post-transcription modification (eukaryotes) – Part 2

Answer 5

• Most eukaryotic genes contain coding and non-coding regions:
• Coding portions (translated into amino acid sequences) = exons
  (expressed regions)
• Non-coding portions (can be long) = introns (intervening regions)
• RNA splicing removes introns and joins exons
• Creates an mRNA molecule with a continuous coding sequence