Genetics Lecture 4

Question 1

Does RNA polymerase require a template?

Answer 1

No.

Question 2

During transcription, what unwinds the DNA?

Answer 2

RNA polymerase has helicase activity.

Question 3

Define the promoter region for transcription initiation. Where is it found?

Answer 3

Site where RNA polymerase attaches. Immediately precedes the transcription initiation site, upstream of the gene.

Question 4

The first site of transcription begins with +1. Where is the promoter region found?

Answer 4

Negative region.

Question 5

What 3 things collectively make a gene?

Answer 5

The promoter, the RNA coding sequence, and the terminator.

Question 6

What direction does RNA polymerase transcribe?

Answer 6

5’ to 3’.

Question 7

Describe the prokaryotic promoter region, including where they are found and the sequence.

Answer 7

Has 2 conserved regions:
At -35 - TTGACA
At -10 - TATAAT

Question 8

In prokaryotes, how does RNA polymerase attach to the promoter region?

Answer 8

A polypeptide called sigma factor binds to the two promoter regions, RNA polymerase binds at -55 to +20. Holoenzyme untwists the DNA at -10, and the sigma factor dissociates.

Question 9

When RNA polymerase is bound to the DNA, where is the DNA untwisted, and by what? What is it called before and after holoenzyme action?

Answer 9

At -10 region by holoenzyme.

Closed promoter complex before untwisting, and opened promoter complex after.

Question 10

As RNA polymerase moves forward transcribing, does the RNA remain bound to the DNA or does it dissociate?

Answer 10

Dissociates as RNA polymerase moves.

Question 11

Which is faster, DNA polymerase or RNA polymerase, and why?

Answer 11

RNA polymerase is slower as it proofreads as it moves forward.

Question 12

How many kinds of RNA polymerases are in prokaryotes vs eukaryotes?

Answer 12

Prokaryotes have one, eukaryotes have three.

Question 13

What are snRNA?

Answer 13

Small nuclear RNA, that binds to some enzymes like telomerases.

Question 14

What type of RNA makes up the most?

Answer 14

rRNA.

Question 15

Which eukaryotic RNA polymerase transcribes mRNA?

Answer 15

RNA polymerase 2.

Question 16

Where is the core promoter in eukaryotes? What is it called, and what kind of sequence is it?

Answer 16

Within 50bp upstream of +1. An initiator sequence called Inr, and has a TATA box.

Question 17

Eukaryotic promoter regions have an additional 2 boxes in addition to the one found in the core promoter. Where are the two found, what are they called, and what sequence are they?

Answer 17

Promoter-proximal elements
CAAT box at -75
GGGCGG at -90

Question 18

What mediates binding of RNA polymerase in eukaryotes?

Answer 18

Transcription factors.

Question 19

How many copies of mRNA are made, just one or many?

Answer 19

Many.

Question 20

How is transcription terminated in prokaryotes?

Answer 20

Stops as soon as the RNA polymerase reaches the termination sequence.

Question 21

How is transcription terminated in eukaryotes?

Answer 21

Transcription continues for an additional 30bp. Is a special sequence that induces a termination hairpin formation, dissociating RNA polymerase.

Question 22

Which of the two, eukaryotes and prokaryotes, have pre-mRNA?

Answer 22

Just eukaryotes.

Question 23

What does pre-mRNA have at the polar ends that mature mRNA doesnt have? Why is it present?

Answer 23

An untranslated region that acts as a buffer, and later modifed to protect the mRNA from exonucleases.

Question 24

What happens to the 5’ end of pre-mRNA? Whats unusual about it, and what does this facilitate?

Answer 24

A capping enzyme adds 2 methylated guanine molecules, an unusual 5’ to 5’ bond, which exonucleases cant break.
Facilitates ribosomal binding.

Question 25

What happens to the 3’ end of pre-mRNA? What does this facilitate and inhibit?

Answer 25

A polyA tail of 50-250 adenine molecules are added.

Inhibits degradation, and facilitates export from the nucleus.

Question 26

What do introns begin and end with that allows then to be spliced?

Answer 26

Begin with GU, and end with AG.

Question 27

What mediates splicing, and what are they? How many are there? Name them.

Answer 27

Small nuclear ribonucleoprotein particles - SnURPs. Are snRNA associated with proteins.
Are 5 of them
U1, U2, U4, U5, U6.

Question 28

Describe how splicing is carried out.

Answer 28

The SNURPs U1 and U2 recognise the GU and AG of introns and bind to them
The other 3 SNURPs bring the U1 and U2 together. The strands are then joined together.

Question 29

Can translation occur at the same time as transcription in prokaryotes and eukaryotes?

Answer 29

Yes in prokaryotes only.

In eukaryotes, it must finish transcription, be exported, and spliced first.