The Process of Transcription

Question 1

What does RNA pol not need to use but DNA pol does?

Answer 1

RNA pol can start a new RNA chain without using a primer

Question 2

Does the whole strand open during translation?

Answer 2

No the DNA only opens within the RNA polymerase (small section at a time)

Question 3

What end of the mRNA leaves the polymerase first?

Answer 3

The 5’ end leaves while the nucleotides are being added to the 3’ end

Question 4

What is the stretch of DNA that is transcribed into an RNA molecule called?

Answer 4

A transcription unit

Question 5

How many types of RNA polymerase do bacteria have?

Answer 5

Bacteria have one type

Question 6

What does the RNA polymerase do in bacteria?

Answer 6

It synthesizes mRNA as well as other types of RNA

Question 7

How many types of RNA polymerases do eukaryotes have?

Answer 7

Eukaryotes have three different types

Question 8

What RNA pol synthesises mRNA in eukaryotes?

Answer 8

RNA pol II

Question 9

What does RNA pol I and II do in eukaryotes?

Answer 9

They synthesis other types of RNA other than mRNA

Question 10

Write a note on RNA polymerase in prokaryotes.

3

Answer 10

Composed of five polypeptide polymerase core enzymes

a, a’, B, B’ and sigma -> all have unique roles

The subunits assemble each time a gene is transcribed and disassemble once transcription is complete

Question 11

What does the sigma subunit of RNA polymerase do?

2

Answer 11

It’s only involved in transcription initiation

It ensures that mRNA is synthesised from an appropriate site

Question 12

What is RNA polymerase called when it is comprised of all five of it’s subunits?

Answer 12

Haloenzyme

Question 13

What does the sigma factor identify?

Answer 13

It recognises the promoter sequence of DNA

Question 14

When does the sigma subunit release?

Answer 14

When polymerase has synthesised 10 nucleotides

Question 15

Do all sigma subunits respond to the same promoter?

Answer 15

No different sigmas respond to different promoters

Question 16

When does RNA polymerase stop?

Answer 16

When it comes across a terminator or stop site

Question 17

What happens when RNA polymerase comes across a terminator site?
(3)

Answer 17

RNA polymerase halts

The DNA template and the newly made RNA chain is released

RNA pol then reassociates with the sigma factor and searches for another promoter to begin the process of transcription again

Question 18

What are the three main steps in transcription in prokaryotes?

Answer 18

Binding and initiation

Elongation

Termination

Question 19

What must happen at the end of transcription in eukaryotes?

Answer 19

mRNA processing must occur before RNA leaves

Question 20

How does initiation of transcription work in eukaryotes?

4

Answer 20

A collection of proteins called transcription factors are needed

They mediate the binding of RNA pol II to promoter

A promoter DNA sequence (TATA box) is crucial for forming the transcription initiation complex

Complex then moves Pol II to start site of gene and begins to polymerise

Question 21

What are transcription factors?

Answer 21

A collection of proteins that mediate the binding of RNA pol II to promoter

Question 22

What is needed to form the transcription initiation complex?

Answer 22

A promoter DNA sequence known as a TATA box

Question 23

What is the main difference between transcription in Eukaryotes vs Prokaryotes?

Answer 23

RNA pol II in eukaryotes doesn’t need a sigma factor but does need transcription factors