Week 3 - Lac Operon

Question 1

Process of transcription

Answer 1

Initiation -> elongation -> termination

Question 2

Eukaryotic transcription

Answer 2

initiation: RNAP binds to promotor forming closed complex
- RNAP forms open complex which is associated with melting of DNA to form transcription bubble
- short transcript will form and then will pause (poised complex)
- RNAP released from poised complex = elongation
elongation - RNAP transcribes gene
termination - RNAP and transcript released so RNAP can resume transcription somewhere else
- signal sent to transcript when polyA site has passed where transcript is cute and polyA site is added to end of transcript
- nuclease rapidly degrades elongating transcript faster than it is elongating

Question 3

what is the transcription bubble?

Answer 3

Where nucleotides are actively added the growing chain

Question 4

Prokaryotic transcription

Answer 4

initiation: RNAP binds to promotor forming closed complex
- there is an additional sigma subunit on RNAP complex which is the promoter seq the complex recognizes –> sigma subunit makes close contact with DNA
- open complex formed through change in conformation, DNA bubble created and sigma subunit revealed
- RNAP in posed complex
- elongation: to get transcription, RNAP needs to be released (POINT OF REGULATION OF GENE EXPRESSION)
- operons often have many cistrons that will give rise to different proteins
- terminator: transcript and RNAP will be released from gene

Question 5

sigma subunit

Answer 5

• allows RNAP to recognize promoter
  no sigma subunit: core enzyme –> no promoter recognition
  sigma subunit present: holoenzyme –> recognizes promoter

Question 6

sigma70

Answer 6

major RNAP contain sigma70 in E.coli

Question 7

simga32

Answer 7

required for heat shock response
- Heat shock genes expressed when temp. rises

Question 8

what are the points of regulation of gene/protein expression in prokaryotes and why?

Answer 8

Elongation and termination because bacterial transcripts are polycistronic

Question 9

terminator

Answer 9

• releases RNAP and transcript from gene

Question 10

If there is a terminator in between cistrons, will the second cistron be expressed?

Answer 10

No only the cistron before terminator 1 will be expressed because if transcription terminates at t1, translation can also not occur

Question 11

what are the points of regulation of gene expression in eukaryotes and why?

Answer 11

Formation of a transcription complex on the promoter
- mediated by presence of regulatory TFs (not basal TFs) on regulatory seq.

Question 12

basal TFs

Answer 12

helps RNAP2 form a poised complex

1. factors to bring RNAP2 to promoter
2. factors to allow RNAP2 to elongate

Question 13

TATA binding protein

Answer 13

binds to the TATA box
- TBP bound to other general TFs assisted bringing RNAP2 close to DNA to bind to promoter

Question 14

TFIIH

Answer 14

important role in released RNAP2