Molecular Biology (5)

Question 1

Name the stages of prokaryotic transcription

Answer 1

Initiation
Elongation
Termination

Question 2

How many RNA polymerases do prokaryotes have and is a primer required?

Answer 2

1

No

Question 3

What are the components of E. coli RNA polymerase holoenzyme?

Answer 3

Core polymerase

Sigma factor

Question 4

What are the subunits of the E. coli core polymerase and what are their roles?

Answer 4

α2ββ'ω
α - scaffolding
β - active site
β' - DNA binding
ω - unknown

Question 5

What is the role of the sigma factor in E. coli RNA polymerase holoenzyme?

Answer 5

Promoter recognition for transcription initiation

Question 6

How many subunits does E. coli sigma factor consist of?

Answer 6

4

Question 7

Which is the most common type of sigma factor?

Answer 7

σ70

Question 8

What does the 3D structure of DNA polymerase resemble?

Answer 8

Hand

Question 9

What does the 3D structure of RNA polymerase resemble?

Answer 9

Crab claw

Question 10

Where are the key regions of the bacterial transcription promoter site?

Answer 10

-10 and -35

Question 11

What is the consensus sequence at -35 nucleotides?

Answer 11

TTGACA

Question 12

What is the consensus sequence at -10 nucleotides?

Answer 12

TATAAT (TATA box sequence)

Question 13

What is the effect of the -10/-35 region being closer to the consensus sequence?

Answer 13

Stronger RNA polymerase binding

Question 14

Which sigma factor binds to the -10 region?

Answer 14

σ2

Question 15

Which sigma factor binds to the -35 region?

Answer 15

σ4

Question 16

What is the significance of the -10 region?

Answer 16

Initial site of DNA melting in active site

Question 17

Where, when, and why does the α subunit bind?

Answer 17

UP element - upstream of -35 region
For genes regularly transcribed - e.g. housekeeping genes
Gives stronger RNA polymerase binding

Question 18

Where does transcription termination occur?

Answer 18

Hairpin loops - from short inverted RNA sequences

Question 19

Name the types of transcription termination

Answer 19

Rho-dependent

Rho-independent

Question 20

What are the intrinsic terminators involved in rho-independent transcription termination and why?

Answer 20

8 A-T bps - following hairpin loop

Weak - RNA easily released from polymerase

Question 21

What is the role of the operator within the promoter region of an operon?

Answer 21

Binds repressor molecule - no transcription

Question 22

What is the role of the activator region of an operon, and where is it located?

Answer 22

Binds activator molecule - upregulates transcription

Upstream of -35 site

Question 23

What does lacZ encode and what is the product’s role?

Answer 23

β-galactosidase - cleaves lactose into glucose and galactose

Question 24

What does lacY encode and what is the product’s role?

Answer 24

β-galactosidase permease - pumps lactose into cell

Question 25

What does lacA encode and what is the product’s role?

Answer 25

β-galactoside transacetylase - not needed for lactose breakdown

Question 26

What is the CAP region of the lac operon?

Answer 26

Activator region

Binds CAP protein