Lecture 10

Question 1

Difference between prok and euk mRNA?

Answer 1

eukaryotes:

1. 7-methylguanosine cap on the 5’ end
2. Poly-adenylation at the 3’ end

prokaryotes:
1. mRNA is polycistronic or contains multiple gene sequences

Question 2

When does pre-mRNA become mRNA?

Answer 2

modification of the 5 prime end (methylguanosine)

addition of the poly-A tail on the 3 prime end

splicing of the exons and the removal of the introns

Question 3

What RNA processing proteins does RNA poly II have?

Answer 3

1. capping factors
2. splicing factors
3. polyadenylation factors

Question 4

What does phosphatase do?

Answer 4

removes one phosphate from the 5’ end of the RNA

Question 5

What does Guanylyl transferase do?

Answer 5

adds a GMP in a reverse linkage (5’ to 5’ instead of 5’ to 3’)

Question 6

What does Guanine-7-methyl transferase do?

Answer 6

adds a methyl group to the 7 position of the terminal guanine

Question 7

What does 2’-O-methyl transferase do?

Answer 7

adds a methyl group to the 2’-O position to the next to last base on the 5’ end

Question 8

why is the 5’ methyl cap important in mRNA regulation?

Answer 8

It helps with processing, transport, and translation

Question 9

What is the function of the 5’methyl cap?

Answer 9

1. regulates export of mRNA out of the nucleus
2. required for the efficient translation of mRNA into protein
3. prevents 5’ degradation

Question 10

3’ mRNA processing-cleavage

Answer 10

1) Cleavage and polyadenylation specificity factor (CPSF) binds to the hexamer AAUAAA (the polyadenylation signal).
2) Cleavage stimulating factor F (CstF) binds the GU-rich element beyond the cleavage site.
3) Cleavage factors bind to the CA sequence at the cleavage site.

Question 11

how does polyadenylation occur?

Answer 11

1. Poly-A-polymerase (PAP) adds approximately 200 A nucleotides to the 3’ end produced by the cleavage
2. Poly-A Binding Proteins (PABP) binds to the poly-A tail and assist in directing translation by the ribosome
3. The cleaved fragment of the RNA is degraded in the nucleus.

Question 12

What is the function of the 3 prime adenylation?

Answer 12

1. increases the half life of the mRNA
2. protects from enzyme attack
3. transcription termination
4. aids in mRNA export out of the nucleus

Question 13

How is intron removal done?

Answer 13

1. 5 snRNAs and other splicing factors mediate splicing
2. The snRNA’s are U1, U3, U4, U5, U6 (bind with the consensus sequences)
3. U1 and U4 leave, thus activating the splicosome
4. U2, U5 and U6 interact to bring neighboring exons
   into correct alignment allowing for two transesterification reactions to occur

Question 14

What are the consensus sequences?

Answer 14

3 prime = AG

5 prime = GU

Question 15

Systemic Lupus Erythematosus

Answer 15

This is an autoimmune disorder where the body attacks its own U1 RNA component of the splicosome, histone, and topoisomerases

symptoms:
fatigue, arthritis, fever skin rashes and kidney problems

Question 16

How can biodiversity be increased in mRNA?

Answer 16

alternative splicing and RNA editing

Question 17

What is alternative splicing?

Answer 17

Splicing the same mRNA strand in different ways to get a different protein

Question 18

explain negative and positive alternative splicing?

Answer 18

positive - an activator protein binds to the mRNA that supports splicing

negative - a repressor bind to the mRNA that inhibits splicing

Question 19

beta-thalassemia

Answer 19

Many individuals with thalassemia have

mutations in the beta-globin gene that generate additional splice sites within the mRNA

Question 20

Limb Girdle Muscular Dystrophy

Answer 20

Some patients with Limb Girdle Muscular Dystrophy possess a mutation in the calpain-3 gene that generates a new splice site within exon 16

shorter mRNA and thus defective protein

Question 21

Chemical modification of mRNA is known as what?

Answer 21

RNA editing

Question 22

What are the two types of RNA editing?

Answer 22

1. Adenosine to Inosine

2. Cytidine to Uridine

Question 23

cytidine deaminase enzyme?

Answer 23

edits the apolipoprotein B, thus their are two forms

Question 24

adenosine deaminase.?

Answer 24

Editing of the glutamate receptor involves a single base change from A to I (inosine). This editing results in a codon change within the mRNA from glutamine to arginine

This editing is required for proper brain development

this editing impacts calcium permeability

Question 25

mutation in intron 1 splice acceptor site?

Answer 25

shorter length mRNA

Question 26

mutation in intron 1 intorduces a splice acceptor site?

Answer 26

longer mRNA

Question 27

Mutation in intron 2 splice donor site?

Answer 27

longer mRNA