Regulation of Gene Expression in Eukaryotes

Question 1

How many RNA polymerases do eukaryotes have?

Answer 1

3

Question 2

What is the function of RNA polymerase II?

Answer 2

Transcribes DNA to pre-mRNA

Question 3

Does transcription need a primer to be initiated?

Answer 3

No

Question 4

What is the function of a promoter in eukaryotes?

Answer 4

Determines the site of transciption initiation and directs binding of RNA polymerase II

Question 5

What are untranslated regions (UTRs)?

Answer 5

Transcribed non-protein coding sequences at mRNA 5’ and 3’ ends

Question 6

Where do activators bind?

Answer 6

To distal control elements

Question 7

What is TBP and what is its purpose?

Answer 7

TATA binding protein, it recruits basal transcription factors which in turn recruit RNA polymerase II

Question 8

When does a transcription bubble form?

Answer 8

After recruitment of helicase

Question 9

What is required for RNA polymerase II to recognise and bind to promoters?

Answer 9

Basal trancription factors

Question 10

What is pre-mRNA made up of?

Answer 10

Introns, exons, and untranslated regions

Question 11

How many maturation processes does pre-mRNA undergo?

Answer 11

3

Question 12

What does a splicesome recognise?

Answer 12

gu…ag sequence within pre-mRNA introns

Question 13

Outline the maturation processes of pre-mRNA

Answer 13

• 5’ met-7G CAP addition
• Pre-mRNA splicing
• 3’ cleavage and polyadenylation

Question 14

What is the advantage of 5’ to 3’ processing?

Answer 14

Promotes mRNA stability and translational efficiency

Question 15

What is alternative splicing?

Answer 15

Mutiple mRNAs can be produced from a single gene resulting in multiple protein isoforms and mutiple interactions

Question 16

How does alternative splicing work?

Answer 16

Joining of different exon combinations (the exons must be sequential)

Question 17

Where are mature mRNA molecules exported from and to?

Answer 17

From the nucleus, to the cytoplasm

Question 18

Are transcription and translation linked in eukaryotes?

Answer 18

No

Question 19

What features of translation are conserved between prokaryotes and eukaryotes?

Answer 19

Codon degeneracy and tRNA charging

Question 20

What does eIF stand for?

Answer 20

Eukaryotic initiation factor

Question 21

What does a eukaryotic ribosome dissociate into?

Answer 21

40s and 60s subunits

Question 22

Do eukaryotes have shine dalgarno sequences?

Answer 22

No

Question 23

How are the 40s and 60s ribosomal subunits kept separate?

Answer 23

eIF3 and eIF6

Question 24

Describe the steps involved in the assembly of the pre-initiation complex at the TATA box

Answer 24

• TATA binding protein is recruited and binds to the core promoter
• TBP recruits basal transcription factors
• These in turn recruit RNA polymerase II
• DNA helicase is then recruited and a transcription bubble is formed

Question 25

Which eIFs are involved in the separation of ribosomal subunits?

Answer 25

eIF3 (binds to 40s subunit) and eIF6 (binds to 60s subunit)

Question 26

Which subunit is involved in the formation of the pre-initiation complex?

Answer 26

40s subunit

Question 27

What eIF is met-tRNAi associated with?

Answer 27

eIF2

Question 28

What form is the met-tRNAi in the pre-initation complex?

Answer 28

GTP form

Question 29

What eIFs are used to help recruit rRNA to the correct position on 40s ribsomal subunit?

Answer 29

eIF1, eIF1A, and eIF5

Question 30

In the initial step of initiation; what happens?

Answer 30

The pre-initiation complex binds to methyl CAP-binding complex

Question 31

What is scanning in the context of initation?

Answer 31

The process by which the pre-initation complex moves along mRNA looking for a start codon

Question 32

What is a Kozak sequence?

Answer 32

* The sequence which must surround the start codon for a pre-initation complex to recognise the AUG * AUG must have a purine at a -3 position * AUG must have a G at a +4 position

Question 33

What occurs when the pre-initation complex finds an AUG in a Kozak sequence?

Answer 33

* It pauses * Hydrolyses GTP and GDP to lock it in place * Allows initation factors around the complex to be released * This allows the 60s subunit to rejoin the complex

Question 34

How is the 60s subunit attached to the 40s subunit?

Answer 34

Brought in by eIF-5B•GTP which is hydrolysed when the subunit binds

Question 35

Which site is the first tRNA put in?

Answer 35

P site

Question 36

Which eEF is responsible for releasing and recycling eEF-1α•GDP?

Answer 36

eEF-1βγ

Question 37

What is the first step in translation elongation in eukaryotes?

Answer 37

eEF-1α•GTP brings a charged aa-tRNA to the A site, the eEF is then hydrolysed

Question 38

What mediates the formation of a peptide bond between the C-terminus of aa in the P site and the N terminus of the aa in the A site?

Answer 38

28s rRNA of the 60s subunit

Question 39

Which eEF is involved in the repositioning of the tRNAs?

Answer 39

eEF2•GTP

Question 40

Outline how translational termination in eukaryotes occurs

Answer 40

* Stop codons recruit eRF1 which binds to the A site and is joined by eRF3•GTP * Hydrolysis occurs to produce eRF3•GDP which causes the peptide chain to be released and the ribosome to dissociate