Lecture 17 Flashcards Preview

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Flashcards in Lecture 17 Deck (25):
1

Where is polymerase I most active?

nucleolus

2

What is RNA polymerase I responsible for?

- makes ribosomal RNA genes (rRNA)

3

What is RNA polymerase III responsible for?

- makes rRNA and tRNA

4

What is RNA polymerase II responsible for?

- makes mRNA
- makes ribosomal proteins

5

What is the role of exosomes?

Degrades abnormal RNA

6

What does miRNA do?

Inhibits translation of mRNA

7

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

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

8

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

Its a 5' to 5' linkage as opposed to 5' to 3'.
- this inhibits ribonuclease activity

9

What is the recognition sequence for poly-adenylation?

- AAUAAA

10

What mediates poly adenylation?

PAP (polyA polymerase)

11

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

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

12

How long is the poly A tail

Around 200 bps long

13

What does the Poly A binding protein do?

It binds the entire poly A tail

14

What does the poly a tail do?

Protects the mRNA from degradation

15

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

5' cap and poly A tail, dude.

16

What percent of mRNA are alternatively spliced?

90%
(alternative splicing is when two mRNA from the same gene can be made up of different exons)

17

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

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

18

What does BcL-xS protein do?

Stimulates apoptosis in lymphocytes

19

What does Bcp-xL protein do?

Inhibits apoptosis in brain

20

What is the sequence at the beginning of introns?

G U

21

What is the sequence at the end of introns?

A G

22

What are the reactions used in splicing?

Two transesterification reactions
(breaking and forming of two phosphodiester bonds)

23

What are the steps of intron splicing?

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.

24

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

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.

25

What are the pathways of eukaryotic mRNA degradation?

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