11.3 transcription (eukaryotic)

Question 1

What are the stages of transcription in eukaryotic cells?

Answer 1

initiation, elongation, and termination (the same)

Question 2

What additional challenges do eukaryotic cells face?

Answer 2

• large number of RNAs that need to be tightly regulated
• the condensed structure of the DNA (chromatin)

Question 3

What makes eukaryotic promoters complicated?

Answer 3

• Very complicated, have lots of regulatory domains
• Regulatory sequences are different for every gene, so it is difficult to build consensus sequences to help us identify these promoters

Question 4

Eukaryotic promoters

Answer 4

• typically there is a core promoter, which can overlap the transcriptional start site.
• there are both upstream and downstream promoter elements
• numerous upstream regulatory elements

Question 5

What is the one consensus sequence that can be found in most promoter regions?

Answer 5

• the TATA box
• consensus: TATAAA

Question 6

How many RNApol do prokaryotes have?

Answer 6

1, with multiple sigma factors

Question 7

How many RNAPs do eukaryotes have?

Answer 7

• 3
• 1 is the main, which transcribes ribosomal rnas
• 2 produces mRNAs and ncRNAs
• 3 produces 5s rRNA, tRNAs and ncRNAs

Question 8

What is the difference in eukaryotics at the promoter region?

Answer 8

• in eukaryotics, it is not just RNA pol that sits down
• instead there are series of proteins called transcription factors that bind to the regulatory elements in a very conserved mechanism
• then RNApol is recruited to the site, creating a complex known as the basal transcription apparatus

Question 9

What is the mediator complex?

Answer 9

• Mediator binds to various regulatory sequences, many of which are distal from the transcriptional start site
• mediator is required for transcription and is involved in unpacking the chromatin to decondensed chromatin that is ready for transcription

Question 10

How was mediator discovered?

Answer 10

• very difficult to study because it is very dynamic and has transient, unessential interactions
• found by roger kornberk

Question 11

Elongation in eukaryotes

Answer 11

• once the basal transcription apparatus leaves the start site, all the transcription factors are released and then transcription can proceed

Question 12

Difference in termination, stem loop mechanism

Answer 12

• different RNAPs use different termination mechanisms
• similar to prokaryotes, a stem-loop structure interferes w RNAP. Common mechanism in tRNAs and ncRNAs

Question 13

Transcription termination in mRNAs

Answer 13

• exonucleases recognize and cleave a polyadenylated sequence in the RNA
• works faster than poly, so the exonuclease bumps the poly off