Transcription in Prokaryotes part 2 Flashcards Preview

MOLECULAR BIOLOGY > Transcription in Prokaryotes part 2 > Flashcards

Flashcards in Transcription in Prokaryotes part 2 Deck (21)
Loading flashcards...
1

Define the promoter

A sequence of nucleotides prior to the gene of interest to which the transcriptional machinery binds

2

What two factors control the formation rate of the DNA-RNA pol. complex?

1. Two consensus sequences in the promoter region
2. Proteins that modify the affinity of the RNA pol. for the promoter

3

What are the positions of the two consensus sequences in the promoter region?

position -10 and -35

4

What is the consensus sequence at position -10

TATAAT

5

What is the consensus sequence at position -35

TTGACA

6

Proteins that increase the affinity of the RNA pol. for the promoter are called...

activators

7

Proteins that decrease the affinity of the RNA pol. for the promoter are called...

repressors

8

Define a "down" mutation

decreases transcription efficiency by shifting the sequence further away from the consensus sequence

9

Define an "up" mutation

Increases transcription efficiency by shifting the sequence closer to the consensus sequence

10

What is the general sigma factor?

Sigma 70

11

Sigma factors control promoter recognition for the RNA pol. How?

Sigma factors are responsible for recognizing the DNA sequence the RNA pol binds to. Thus, substitution of a sigma factor causes the RNA pol to recognize a different set of promoters

12

How many different sigma factors did he show us? What was the takeaway from that?

Five.
- Each sigma factor recognizes different sequences at the -10 and -35 positions
- One general sigma factor (sigma 70) used most of the time

13

What are the two types of promoters

1. Typical promoter
- holoenzyme is bound to DNA @ sequences -10 and -35
2. Promoter with activator site
- An activator site, usually upstream (sometimes between -35 and -10), contains a sequence where an activator protein can bind.
-This activator, once bound, interacts with the sigma factor

14

What are the two types of supercoiling?

1. Negative supercoiling (behind site of transcription)
-helix opening facilitated
2. Positive supercoiling (in front of site of transcription
- helix opening hindered

15

Define the role of gyrase with regards to supercoiling

Helps task of RNA pol be creating overall NEGATIVE supercoiling on the DNA strand

16

Define the role of topoisomerase with regards to supercoiling

Returns excessive negative levels of supercoiling to normal coiling levels

17

What are the three types of terminators?

1. Intrinsic terminator
2. Rho-dependent terminator
3. Antitermination

18

List three characteristics of an intrinsic terminator

1. part of the strand being synthesized
2. Two major structural features: hairpin structure and 6 Us near hairpin
3. Once hairpin is formed, it bends around and interacts with RNA pol, halting transcription

19

List some characteristics of Rho-dependent terminators

1. Rho protein is a hexamer, binding to RUT site on freshly synthesized RNA
2. The RUT site they bind to is C-rich, G-poor
3. Rho uses helicase to separate DNA from RNA

20

How does Rho terminate transcription

-while RNA pol is paused at a hairpin, Rho catches up by moving up mRNA.
- Rho then unwinds DNA-RNA hybrid

21

What is antitermination?

A property of RNA pol that allows it to ignore a termination sequence and continue synthesis.
- certain proteins need to bind in order for this result to occur.