Eukaryotic transcription

Question 1

What is the excpetion to the difference between Bacterial and Eukaryotic transcription?

Answer 1

some bacterial mRNAs are modified.Eg rRNA and tRNA are processed from a primary transcript.

Question 2

What is the difference between Bacterial and Eukaryotic DNA transcription, in context of modification of the transcripted mRNA

Answer 2

Bacterial DNA is NOT modified before translation. Eukaryotic transcription also occurs within the nuclear membrane.

Question 3

what does rRNA code for?

Answer 3

the constiuent elements of ribosomes.

Question 4

what does tRNA do?

Answer 4

carry the complemetary amino acid for the codon base sequence on the mRNA molecule.

Question 5

What happens in the modification/processing of mRNA before translation?

Answer 5

Introns(non-coding0 are removed to leave exons(coding) segments of mRNA via splicing.

5’ cap added and the addition of a polyadenylated tail at 3’ end.

Question 6

explain the process of 5’capping during the processing of mRNA

Answer 6

the 5’ triphosphate on the 5’ end of mRNA is modified: one phosphate group is removed and the resulting diphosphate attacks a GTP (guanine triphosphate), forming an unusual 5’-5’ triphosphate linkage.
Therefore no obvious 5’ end for 5’ exonucleases to degrade mRNA.

Question 7

what is the difference between endo and exonucleases

Answer 7

exonucleases - attack form either 5’ or 3’ directions, EG. RNA Pols.

endonuclease - attacks the phosphodiester bonds between nucleotides, eg DNase.

Question 8

Explain the process of adding the poly(A) tail during modification

Answer 8

at the 3’ of the primary mRNA transcript, it is cleaved at the cleavage signal(AAUAAA), by a specific endonuclease. poly(A) tail is then added using ATP.

Question 9

what is the effect of a longer Poly(A) tail?

Answer 9

protects against degradation longer

Question 10

What are the two types if eukaryotic RNA Pol II promoters

Answer 10

TATA box promoters
TATA-less promoter

Question 11

what are the additional variation of eukaryotic RNA pol II promoters

Answer 11

CAAT box sequence or GC box sequence.
between -40 to -150 bs.

Question 12

What are the components and locations of components of the TATA box promoter?

Answer 12

enhancers - several kb away

TATA box/sequence - between -30 to -100 bs from transcriptional start.

Inr- Initiator element, after the TATA box

Question 13

How does bacterial transcription and eukaryotic transcription differ, in context with RNA Polymerase

Answer 13

Bacterial transcription uses the incorporation of a sigma unit to bind specifically to the promoter region.

Eukaryotic transcription recognise promoters using General Transcription Factors which are bound to RNA Pol II/

Question 14

What is the first transcription factor to bind onto RNA Pol II

Answer 14

TFIID - Transcription Factor (RNA Polymerase)II D

Question 15

what is the role of TFIID in the initiation stage of transcription

Answer 15

Forms a complex w RNA Pol II which allows bends DNA and contains TATA-box binding proteins(TBP) to tightly bind to the TATA box of the promoter region.

TFIID acts a recruitment vessel for further transcription factors.

Question 16

What happens during the Initiation stage of eukaryotic transcription

Answer 16

TFIID recruits TFIIA and TFIIB, which bind to TBP

TFIIB recruit TFIIF, RNA Pol II, TFIIE and TFIIH.

All of these transcription factors form the ‘Basal Transcription Apparatus’

Question 17

What are the functions of TFIIH

Answer 17

1. it acts as a helicase, unwinding the DNA double helix
2. It acts a kinase, phosphorylating the CTD( c’ terminus domain), which signifies the switch into elongation.

Question 18

What changes in the Basal transcriptional appartatus’ structure during elongation?

Answer 18

TFIIB, E, H dissociate and RNA synthesis occurs,
After a few nucleotides, RNA Pol II progresses, freeing the promoter and TFIID/A complex for further recruitment.

Question 19

What are the role of enhancers?

Answer 19

they act as a level of transcriptional control across long distances, turning ‘on/off’ genes.

Question 20

What model allows enhancers to interact with RNA Pol II

Answer 20

DNA looping model

Question 21

What are the two types of elements enhancers can have

Answer 21

1. enhancer control elements that bind to activator proteins which then interact with the mediator proteins.

2.silencer control elements that bind to repressor proteins which DONT interact with mediator proteins.

Question 22

which state of transcription do enhancers function

Answer 22

initiation state, with mediator proteins interacting with unphosphorylated CTD of the RNA Pol II.

Question 23

What is the role of the mediator protein with enhancers.q

Answer 23

mediator proteins allow condensed chromatin to remain decondensed to allow the transcription of the gene. turning the gene ‘on’.

Question 24

What is the other method of transcriptional level control.

Answer 24

the Acetylation of histone tails. this allows the chromatin to be loose.

Question 25

Explain the combinatorial control of gene activation.

Answer 25

specific activator proteins are required to bind to enhacer control elements, therefore only specific cells w specific activators present can interact with mediator proteins and allow the gene to be expressed.

Question 26

What is the difference between the nature of bacterial and eukaryotic mRNAs

Answer 26

bacterial mRNAs are polycistronic, code for multiple proteins.
Eukaryotes are monocistronic.

Question 27

In a Eukaryotic Cell are mRNA molecules transcripted and translated simultaneously?

Answer 27

no, eukaryotic transcription in nuclear and translation is cystolic,

Transcription and translation in bacteria CAN happen simultaneuosly due to the lack of compartmentalisation.