Transcription In Eukaryotes

Question 1

3 similarities between transcription in prokaryotes and eukaryotes

Answer 1

1. Both require DNA template
2. RNA polymerase responsible for transcription in both
3. Informtaion from DNA copied onto RNA

Question 2

Where is the TATAA box located

Answer 2

-25 region and -75 region is CAAT box

Question 3

Where is RNAP 1 located and what is its function

Answer 3

Located in the nucleolus
Responsible for rRNA transcription, processing and assembly
Synthesizes all rRNA molecules except 5S rRNA molecule

Question 4

RNAP II location and function

Answer 4

Nucleus and sysnyhesises protein coding RNA. mRNA
Transcribing majority of eukaryotic Gene’s
And also genes for several regulatory RNAs , microRNAs and long coding RNAs

Question 5

RNAP III location and function?

Answer 5

Nucleus
5S pre rRNA
Pre tRNA
small nuclear pre RNAs(responsible for spilling and regulation transcription factors)

Question 6

What is the transcription pre initiation complex?

Answer 6

Refers to the complete assembly of transcription factors and RNA polymerase bound to the promoter region

Question 7

TFIID binds to prompter region first. Why?

Answer 7

Presence of tata binding protein subunit which binds to to the tata box along with TFIID

Question 8

After TFIID binds, which other 5 transcription factors bind and in what order

Answer 8

TFIIB, TFIIE, TFIIH, TFIIA, TFIIF(comes along with RNAP II)

Question 9

How many protein subunits has RNAP II

Answer 9

12

Question 10

Transcription bubble consists of about how many bp

Answer 10

25

Question 11

Distinguish between introns and exons

Answer 11

Introns are the non coding regions of genes and exons are the coding regions of genes

Question 12

Why is freshly formed mrna called pre mRNA.

Answer 12

Because processing is yet to occur

Question 13

What is processing?

Answer 13

Removing introns and joining exons together

Question 14

There are structures added to the ends of the mRNA. What are they

Answer 14

Polyadenyl tail in a process called polyadenylation to the 3’ end and Guanine cap to the 5’ end

Question 15

When does polyadenylation begin

Answer 15

Begins as the gene terminates

Question 16

How is transcription terminated in RNAP 1

Answer 16

the rRNA genes transcribed contain a sequence of specific 11 BP which are recognized by Transcription Termination Factor 1. Binds the DNA at that sequence preventing further transcription and causing RNA and RNAP1 to disengage

Question 17

How is transcription terminated in RNAP II

Answer 17

Genes Lacks specific sequence that direct RNAP II to terminate at specific places
Can transcribe up to 1000 bp past actual end of gene
Transcript cleaver at internal site before RNAP II finishes transcribing
Releases upstream portion of mRNA
Remainder of transcript is digested by a 5’ exonuclease (Xrn2) in humans while transcription still taking place
Exonuclease catches up with RNAP by digesting overhanging RNA and helps disengage RNAP II

Question 18

READ SLIDE 28 AND 29

Answer 18

.

Question 19

Why are death cap mushrooms deadly

Answer 19

They produce a toxin, amanitin which inhibits RNAP II

Question 20

What is Rifampicin

Answer 20

It is an antibiotic which inhibits RNAP in bacteria

Question 21

Poly A tail function?

Answer 21

Makes RNA more stable and prevents its degradation
Additionally, the poly-A tail allows the mature messenger RNA molecule to be exported from thenucleusand translated into aproteinbyribosomesin thecytoplasm.

Question 22

Which enzyme is responsible for the addition of the 3’ poly A signal

Answer 22

The Poly(A) polymerase enzyme

Question 23

What is the function of the G cap

Answer 23

The 5’ cap is added to the first nucleotide in the transcript during transcription. The cap is a modified guanine (G) nucleotide, and it protects the transcript from being broken down. It also helps the ribosome attach to the mRNA and start reading it to make aprotein.

Question 24

Enhancer?

Answer 24

Anenhanceris a DNA sequence that promotestranscription.

Question 25

Silencer?

Answer 25

Enhancers have the ability to greatly increase the expression of genes in their vicinity. More recently, elements have been identified that decrease transcription of neighboring genes, and these elements have been called silencers.

Question 26

For protein encoding Gene’s, the cleavage site which determines the end of the emerging pre mrna occurs where?

Answer 26

Between an upstream AAUAAA sequence and a downstream GU rich sequence separated by about 40 to 60 nucleotides in the emerging RNA

Question 27

Which proteins bind to the AAUAAA sequence and the GU rich sequence respectively

Answer 27

The CPSF protein and the Cstf protein. They form the base of a protein complex that form in this region before CPSF cleaves the nascent pre mrna at a site 10 to 30 nucleotides downstream the AAUAAA site