Transcription in Prokaryotes

Question 1

What are the products of transcription?

Answer 1

mRNA
rRNA
tRNA
ncRNA

Question 2

What are the requirements for RNA synthesis?

Answer 2

DNA Template
4 NTPs
Mg²⁺ or Mn²⁺
RNA Polymerase

Question 3

What are the enzymes capable of RNA synthesis?

Answer 3

RNA Polymerase (Transcription)
Primase (for DNA replication)

Question 4

RNA is synthesized from its ____-end to its ____-end

Answer 4

__5’__
__3’__

Question 5

RNA is complementary to the ____ strand and identical to the ____ strand (with U replacing T)

Answer 5

__antisense/minus/DNA template__
__sense/plus/coding__

Question 6

What does transcription by RNA polymerase involve?

Answer 6

A Core Enzyme
Several Auxiliary Proteins

Question 7

What are the 5 peptides which forms the core enzyme?

Answer 7

2α
1β
1β’
1ω

Question 8

What are the functions of the five peptides forming the core enzyme?

Answer 8

Enzyme Assembly
Template Binding
5’ → 3’ Polymerase Activity

Question 9

What can the core enzyme not accomplish?

Answer 9

It cannot recognize the promotor region of the DNA template

Question 10

What is a Holoenzyme?

Answer 10

RNA polymerase + Sigma Factor

Question 11

Function of Holoenzyme

Answer 11

Capable of recognizing promotor region on DNA

Question 12

What are the steps of RNA Synthesis?

Answer 12

Initiation
Elongation
Termination

Question 13

Initiation
What happens during initiation?

Answer 13

RNA Polymerase Holoenzyme binds to Promotor Region

Question 14

Initiation
What are the Prokaryotic Promotors?

Answer 14

-35 Sequence - Consensus sequence 35bp left of transcription start site
Pribnow Box - Consensus about 10 bp upstream of transcription start site. It is the site of DNA melting

Question 15

Elongation
Steps of Elongation

Answer 15

DNA Helix unwinds by RNA Polymerase
Synthesis of RNA begins
DNA-RNA hybrid helix is formed in 5’ → 3’ direction
Growing chain dissociates from DNA
DNA Helix rewinds

Question 16

Elongation
Characteristics of RNA Polymerase activity

Answer 16

Does not need primer
Has no exonuclease activity

Question 17

Elongation
Carried out by Core Enzyme or Holoenzyme?

Answer 17

Core Enzyme

Question 18

Elongation
Errors during elongation

Answer 18

RNA Polymerase pauses, backtracks, cleaves transcripts and restarts

Question 19

Termination
Where does Elongation continue until?

Answer 19

Until Termination Signal is reached

Question 20

Termination
Which protein is responsible for Termination?

Answer 20

Rho Factor

Question 21

Termination
Rho Factor function

Answer 21

Separates DNA-RNA hybrid

Question 22

What does pro RNA do after Termination?

Answer 22

Self-complementary pro RNA causes hairpin structure

Question 23

Antibiotics inhibiting RNA Polymerase

Answer 23

Rifampicin