Lecture 11. Bacterial Transcription

Question 1

When can gene expression be regulated?

Answer 1

At the level of transcription or translation or both

Question 2

Non-template strand

Answer 2

Sense strand

Question 3

Template strand

Answer 3

Antisense strand

Question 4

Why is uracil not found in DNA?

Answer 4

Uracil is removed by uracil-DNA glycosylase

Question 5

mRNA (messenger RNA)

Answer 5

Encodes proteins

Question 6

rRNA (ribosomal RNA)

Answer 6

Constituents of ribosomes: role in protein synthesis

Question 7

tRNA (transfer RNA)

Answer 7

Adaptors between mRNA and amino acids: role in protein synthesis

Question 8

How many classes of RNA molecules are synthesised in bacteria?

Answer 8

3

Question 9

How many RNA polymerases are involved in the synthesis of RNA molecules?

Answer 9

1

Question 10

When can translation and transcription take place in a bacteria?

Answer 10

Simultaneously

Question 11

5’ promoter

Answer 11

Attracts and binds RNA polymerase

Question 12

Protein-coding sequences

Answer 12

Often multiple genes - polycistronic - as part of an operator

Question 13

3’ terminator

Answer 13

Signals the stop point for transcription

Question 14

Bacterial core RNA polymerase is composed of what subunits and in what ratio?

Answer 14

α, β, β’, ω - 2:1:1:1

Question 15

Which subunit converts the enzyme to holoenzyme?

Answer 15

σ

Question 16

How does the core RNA polymerase bind to DNA and why does it bind this way?

Answer 16

Non-specifically to allow sliding

Question 17

What subunit binds to the core polymerase and why?

Answer 17

A σ subunit to direct the polymerase holoenzyme to a gene promoter

Question 18

Basis of the DNA footprinting technique that was used to identify promoters

Answer 18

Bind RNA polymerase holoenzyme to DNA in vitro and then add nuclease to degrade all DNA except the stretch bound t the polymerase as it has become protected

Question 19

What are the two regions protected by RNA polymerase and where are they centred?

Answer 19

-10 sequence (-10 bp from the start of transcription)
-35 sequence (-35 bp from the start of transcription)

Question 20

-35 sequence

Answer 20

TTGACA

Question 21

-10 sequence

Answer 21

TATAAT

Question 22

Which strands are the consensus sequences defined on?

Answer 22

Sense strand

Question 23

What are the stages of transcription?

Answer 23

Initiation, Elongation and Termination

Question 24

Initiation

Answer 24

RNA polymerase holoenzyme binds the promoter, opens the DNA double helix and starts to transcribe

Question 25

Elongation

Answer 25

The σ subunit disengages from the holoenzyme, and the core enzyme continues to make new RNA

Question 26

Termination

Answer 26

RNA polymerase core enzyme dissociates from the DNA, and transcription halts

Question 27

Why does E. coli have multiple σ subunits?

Answer 27

Different σ factors recognised different promoters, so they provide specificity

Question 28

Which gene does the σ subunit RpoH control and how many genes are controlled?

Answer 28

Heat shock, ~40

Question 29

Initiation process

Answer 29

The polymerase pulls downstream DNA towards itself scrunching the DNA until success where the -10 region is opened. Converting the closed promoter complex to an open promoter complex. Unlike the action of DNA helicase, this step does not involve the energy of ATP hydrolysis.

Question 30

Rate of elongation

Answer 30

50 nucleotides/sec

Question 31

Error rate of RNA polymerase

Answer 31

One mistake around every 10⁴ - 10⁵ nucleotides

Question 32

The 2 mechanisms involved in the termination of transcription

Answer 32

ρ-independent and ρ-dependent

Question 33

Inhibitor of prokaryotic transcription

Answer 33

Rifampicin