Lecture 17

Question 1

Where is polymerase I most active?

Answer 1

nucleolus

Question 2

What is RNA polymerase I responsible for?

Answer 2

• makes ribosomal RNA genes (rRNA)

Question 3

What is RNA polymerase III responsible for?

Answer 3

• makes rRNA and tRNA

Question 4

What is RNA polymerase II responsible for?

Answer 4

• makes mRNA

- makes ribosomal proteins

Question 5

What is the role of exosomes?

Answer 5

Degrades abnormal RNA

Question 6

What does miRNA do?

Answer 6

Inhibits translation of mRNA

Question 7

What are the steps of 5’cap on eukaryotic mRNAs?

Answer 7

1) phosphohyrolase removes the gamma phosphate from the pre-mRNA
2) GTP gets cleaved, losing two phosphates and subsequently binds to the beta phosphate on pre-mRNA
3) Guanine from GTP gets methylated from S-adenosine-methionine

Question 8

What is unusual about the 5’cap on eukaryotic mRNA? Why is this important?

Answer 8

Its a 5’ to 5’ linkage as opposed to 5’ to 3’.

- this inhibits ribonuclease activity

Question 9

What is the recognition sequence for poly-adenylation?

Answer 9

• AAUAAA

Question 10

What mediates poly adenylation?

Answer 10

PAP (polyA polymerase)

Question 11

Where does the recognition sequence for poly-adenylation actually appear on the DNA sequence?

Answer 11

10-30 bases upstream of the site that actually gets polyadenylated

Question 12

How long is the poly A tail

Answer 12

Around 200 bps long

Question 13

What does the Poly A binding protein do?

Answer 13

It binds the entire poly A tail

Question 14

What does the poly a tail do?

Answer 14

Protects the mRNA from degradation

Question 15

Where is the methylated cap found on the mRNA and where is the poly A tail found?

Answer 15

5’ cap and poly A tail, dude.

Question 16

What percent of mRNA are alternatively spliced?

Answer 16

90%

alternative splicing is when two mRNA from the same gene can be made up of different exons

Question 17

What are three ways to alternative splicing can alter the mRNA derived from the same gene?

Answer 17

1) removal of exons on the interior of the mRNA
2) removal of exons near a poly U recognition sequence
3) use of different promoter regions

Question 18

What does BcL-xS protein do?

Answer 18

Stimulates apoptosis in lymphocytes

Question 19

What does Bcp-xL protein do?

Answer 19

Inhibits apoptosis in brain

Question 20

What is the sequence at the beginning of introns?

Answer 20

G U

Question 21

What is the sequence at the end of introns?

Answer 21

A G

Question 22

What are the reactions used in splicing?

Answer 22

Two transesterification reactions

breaking and forming of two phosphodiester bonds

Question 23

What are the steps of intron splicing?

Answer 23

1) A 2’ hydroxyl from the 3’ exons (latter exons) nucleophilic attacks the phosphate nearest the 5’ exons (former exons), cleaving the strand.
2) the 3’ hydroxyl from the now hanging 5’ exon nucleophilic attacks the 3’ exons (latter exons) and forms the final mRNA strand.

Question 24

How does the HIV virus get around the fact that RNAs have to get completely spliced?

Answer 24

Through the use of the protein Rev which causes the viral RNA to be exported from the nucleus before it gets a chance to get spliced.

Question 25

What are the pathways of eukaryotic mRNA degradation?

Answer 25

• Deadenylation
• Recapping
• Endonucleases
• nonsense-mediated mRNA decay via premature termination codons