1. Prokaryotic and Eukaryotic Transcription

Question 1

what is the transcription rate

Answer 1

about 1,000 nucleotides per minute

Question 2

Describe the initiation stage of dna transcription in prokaryotes

Answer 2

The RNA polymerase binds to a promotor with a sigma factor to being transcription

Question 3

describe the elongation stage of transcription in prokaryotes

Answer 3

the RNA polymerase transcribes, adding to the 3’ end but sigma isn’t needed anymore. the helix unwinds and winds after the sigma leaves

Question 4

describe the termination stage of transcription in prokaryotes

Answer 4

in prokaryotes we have rho-independent and rho-dependent termination which results in the leaving of the the RNA polymerase.

Question 5

structural differences btwn eukaryotes and bacteria

differences btwn eukary and bacteria in transcription

Answer 5

prokaryotes- lack cell nucleus or membrane bound organelles.
no histones or nucleosomes

• prokary use promoters
• prokary transcription occurs simultaneous to translation

Question 6

describe the promotor sites for bacteria?

Answer 6

promoter sites:
-10 is upstream and is pribnow box or TATATA
-35 is also upstream and has a consensus sequence as well
we also have a initiation site which is +1 downstream

Question 7

when does the prokaryote RNA polymerase release the sigma factor?

Answer 7

usually after about 10 nts are transcribed. just need it for initiation, not for elongation

Question 8

describe rho-independent termination for the prokaryote but also include how it relates to eukaryotes

Answer 8

1. RNA poly meets hairpin which is GC rich and is followed by lots of Us
2. RNA poly transcribes lots of As
3. bond btwn A and U is weak so RNA poly falls off

in eukary: poly III uses this …think “has lots of dependents”

Question 9

describe rho-dependent termination for the prokaryote but also include how it relates to eukaryotes

Answer 9

1. RNA poly meets hairpin of inverted sequence
2. RNA poly slows down …but this is not enough
3. sigma protein scoops in and help kick off the RNA poly

in eukary: poly I uses this (think dependent bc 1)

Question 10

describe the use of operons for tryptophan gene
-describe what happens when tryp is high and low

-describe the options for termination

Answer 10

a) scenario when tryptophan is high:
- you have lots of tryptophan in the cell therefore it will bind to the repressor. This conformation change in the repressor protein increases its affinity for the operon
- tyr-repressor complex binds to the operator and physically blocks the RNA poly from binding

b) when tryphan levels are low:
- we want to continue transcription bc tryp levels are low:
- so before we get to the leader sequence, we have a hairpin from btwn region 1 and 2 and this prevents the 3 and 4 loop from forming
- therefore we have transcription continue

When want to stop transcription:

a)AFTER WE TRANSCRIBED the LEADER sequence…but they they are high so now we want to stop:

• a secondary structure forms btwn region 3 and region 4
• so 3 and 4 binding is actually hallmark for stopping transcription (after it has begun and tryp levels are now high) so when this forms, the RNA poly falls off