L7

Question 1

Pre-rRNA(45s) is synthesized by

Answer 1

RNA polymerase I.

Question 2

____ proceeds in the ___ to form 28S,18S, and 5.8S rRNAs. BUT NOT 5S

Answer 2

REMEMBER THAT 5S IS WITH tRNA

pre-rRNA 45s - nucleolus

Question 3

What are the three steps of Pre-rRNA Processing?

Answer 3

1- cleavage by ribonuclease
2- trimmed by exonuclease
3- Base and sugar modification by snoRNA

Question 4

What are re the 4 steps for processing tRNA

Answer 4

1- 16 ntd sequence at the 5’ is cleaved by RNase P
2- 14 ntd INTRON in the anticodon is removed by nuclease
3- U residues at 3’ are replaced by CCA
4- many bases are converted

Question 5

The hnRNA undergo extensive co- and post- transcriptional modifications in the___.

Answer 5

nucleus

Question 6

modifications of hnRNA usually include

Answer 6

1- 5’ capping
2- 3’poly-A-Tail addition
3-removal of introns (splicing)

Question 7

Which is larger? hnRNA or mRNA

Answer 7

hnRNA

Question 8

Is not transcribe

Answer 8

Cap + pol A tail

Question 9

Capping is mostly

Answer 9

G ntd

Question 10

The cap is made up of

Answer 10

7-methylguanosine added “backward” in a 5’→ 5’ triphosphate linkage

Question 11

Triphosphate min ween?

Answer 11

2 from the original base
1 from the cap

Question 12

Addition of GMP, cap is by

Answer 12

Guanylyltransferase

Question 13

A methyl group is added to the cap by

Answer 13

Guanine-7-methyltransferase

Question 14

Is not found in the gene sequence

Answer 14

Cap

Question 15

Function of cap

Answer 15

Aids in mRNA stabilization
Facilitates initiation of translation

Question 16

Why do we add the +5 phosphate cap

Answer 16

Recognize by ribosome
Movement
Protects 5’ end of mRNA

Question 17

Where is the hn-mRNA is cleaved?

Answer 17

after the “polyadenylation signal sequence” (AAUAAA).

Question 18

40–200 Adenine (A) nucleotides are added to the 3‘ end and it id catalyzed by ___ and uses ___as substrate.

Answer 18

Polyadenylate polymerase (Poly A Pol)
ATP

Question 19

Function of pol A tail

Answer 19

-Facilitates mRNA transport out of the nucleus
– Stabilizes the mRNA
-Aids in translation —> ribosomes recognize the poly A tail to stop translating

Question 20

Interpret: the more poly A tail is there the more stable the mRNA is

Answer 20

Nuclease eats mRNA, so when they find a short poly a tail they chew it fast and ruin it but when there are a lot of poly a tail sequences it takes a longer time to damage the mRNA

Question 21

Removal of introns (non-coding sequences) and joining of exons (coding sequences) to form the mature mRNA is known as

Answer 21

mRNA splicing

Question 22

What is the intron structure

Answer 22

5’ Splice site: 5’ GU 3’
3’ Splice site: 5’ AG 3’
Branch Point A

“Guag”

Question 23

What splices hnRNA?

Answer 23

snRNPs

Question 24

Spliceosome

Answer 24

The molecular complex that accomplishes the splicing mechanism.

Question 25

What is the mechanism of splicing

Answer 25

snRNPs recognize 5’
snRNPs recognize 3”
snRNPs Recognize Branch site
Spliceosome
2’ of exon 2(3) attack 3’ of exon1(5) - 2’-5’ bond
3’ of exon 1(5) attacks 5’ of exon 2 (3) - Join 1 and 2