Ch. 17c RNA Processing & Transcription Regulation (Exam 2)

Question 1

What does post-transcriptional gene control mean?

Answer 1

All processes regulating gene expression after the start of transcription

Question 2

What are the 3 main processes of pre-mRNA processing?

Answer 2

1) 5’ capping
2) Polyadenylation
3) Intron splicing

Question 3

What is a 5’ cap?

Answer 3

Modification of the 5’ on the primary transcript (pre-mRNA)

Question 4

What does a 5’ cap create?

Answer 4

7-methylguanylate (m7Gppp) attached to the first nucleotide of the pre-mRNA

Question 5

How does m7Gppp link to the first nucleotide of pre-mRNA?

Answer 5

5’-5’ linkage that links the 5’C of one pentose to another

Question 6

What are 3 purposes of the 5’ cap?

Answer 6

1) Transport of mRNA to cytoplasm
2) Protect against nuclease
3) Start translation

Question 7

M7Gppp is an example of a…

Answer 7

Nucleoside triphosphate

Question 8

What 4 things does the 5’ cap structure influence in mRNA?

Answer 8

1) Stability
2) Splicing
3) Export
4) Translation

Question 9

Pre-mRNA is the primary transcript with the same organization as…

Answer 9

The gene

Question 10

What is splicing?

Answer 10

Removal of introns to turn pre-mRNA into mature mRNA

Question 11

What is the purpose of the pre-mRNA splice sites?

Answer 11

To help direct splicing reactions

Question 12

Where is the 5’ splice site?

Answer 12

On the 5’, left end of the intron

Question 13

What consensus sequence does the 5’ splice site include (HINT: 2 nucleotide bases)?

Answer 13

GU

Question 14

Where is the 3’ splice site?

Answer 14

On the 3’, left end of the intron

Question 15

What consensus sequence does the 3’ splice site include?

Answer 15

AG

Question 16

Is the central region of the intron important for splicing?

Answer 16

Generally, no

Question 17

What does the GU-AG rule describe?

Answer 17

The requirement of these dinucleotides at the 5’ and 3’ splice sites respectively so that they come together after splicing

Question 18

What 3 things does splicing require?

Answer 18

1) 5’ splice site
2) 3’ splice site
3) Branch site

Question 19

What is the purpose of the branch site?

Answer 19

To initiate a nucleophilic attack on the 5’ splice site

Question 20

Splicing requires 2 { } reactions.

Answer 20

Transesterification

Question 21

What happens in the first transesterification reaction?

Answer 21

Nucleophilic attack from branch site OH group cleaves phosphodiester bond at 5’ splice site

Question 22

What happens in the second transesterification reaction?

Answer 22

3’ OH group of 5’ exon does nucleophilic attack at the 3’ splice site

Question 23

What is the major product of transesterification?

Answer 23

Spliced exons

Question 24

What is the minor product of transesterification?

Answer 24

Lariat product

Question 25

What does the lariat product consist of?

Answer 25

Excised intron

Question 26

What does the acronym snRNA stand for?

Answer 26

Small nuclear RNA

Question 27

How many snRNAs does splicing require? What are they?

Answer 27

5; U1, U2, U4, U5, U6

Question 28

What does the acronym snRNP stand for?

Answer 28

Small nuclear ribonucleoprotein particles

Question 29

What is a spliceosome?

Answer 29

Complex of all 5 snRNAs and pre-mRNA

Question 30

What does the complex on the pre-mRNA intron consist of?

Answer 30

1) U1 on 5' splice site 2) SF1 & U2AF on branch point A 3) 3' AG dinucleotide

Question 31

What is the first step of splicing with the spliceosome complex?

Answer 31

Splicing factor 1 (SF1) moves out, and U2 is added in

Question 32

After the U2 snRNP is added to the pre-mRNA, what happens in the second step of splicing?

Answer 32

U4-6 are added on to fully form the spliceosome

Question 33

After the spliceosome fully forms, what is the third step of splicing?

Answer 33

U1 & 4 move out, and the pre-mRNA gets ready for splicing

Question 34

After U1 & U4 are gone from the pre-mRNA, what are the 4th and 5th steps of splicing?

Answer 34

Transesterification

Question 35

After transesterification, what is the 6th step of splicing?

Answer 35

Debranching w/ debranching enzyme to cleave 2'-5' branch point

Question 36

What is the point of cleaving the 2'-5' branch point?

Answer 36

Expelling the lariat

Question 37

What are the 2 purposes of the poly(A) tail after 3' cleavage and polyadenylation?

Answer 37

Nuclear transport & translation

Question 38

How is eukaryotic gene expression controlled?

Answer 38

Initiating transcription by opening up the chromatin

Question 39

On what 3 occasions/circumstances will mRNA be regulated?

Answer 39

1) Transportation to the cytoplasm 2) Translation 3) Degradation

Question 40

Controlling eukaryotic gene expression determines which form of a { } is represented in mRNA.

Answer 40

Gene

Question 41

This chemical reaction, which involves the introduction of an acetyl group, is associated with gene activation...

Answer 41

Acetylation

Question 42

What is the relationship between transcription factor concentration, chromatin condensation, & transcription?

Answer 42

Higher concentration = less condensation = open for transcription

Question 43

In acetylation, acetyl groups are added to the positively-charged side chain of this amino acid...

Answer 43

Lysine

Question 44

Are acetyl groups added to the C-terminal or N-terminal of the core histone?

Answer 44

N-terminal

Question 45

What is the relationship between histone binding strength and transcription activity?

Answer 45

Weaker histone binding = greater transcription activity

Question 46

What are nucleosome remodeling factors?

Answer 46

Protein complexes that facilitate the binding of transcription factors by altering nucleosome structures

Question 47

What is the mechanism of action of nucleosome remodeling factors?

Answer 47

Science isn't sure yet, but these factors appear to allow proteins easier access to nucleosomal DNA without removing histones

Question 48

What hypothesis may answer how the nucleosome remodeling factors help transcription factor binding (HINT: they catalyze something)?

Answer 48

They catalyze the sliding of histone octamers along DNA

Question 49

How does DNA methylation control transcription?

Answer 49

Methylation reduces transcription activity, which means that the chromatin are more condensed

Question 50

How does protein MeCP2 function?

Answer 50

It works with histone deacetylase, which alters nucleosome structure, and inhibits transcription activity i.e. it's a gene repressor