RNA processing (exam 2)

Question 1

5’ cap

Answer 1

7-methyl-guanosine cap
Provides handle for ribosomes to attach for translation
Protects mRNA from endonucleases

Question 2

How does 7-methyl-guanosine link to 5’ end?

Answer 2

5/,5’ triphosphate link

Question 3

Polyadenylation

Answer 3

poly A tail on 3’ end
Molecular condensation with GTP with the 5’NTP

Question 4

Capping enzyme

Answer 4

Guanylyl transferase

Question 5

Poly A tail cleavage signal

Answer 5

AAUAAA

Question 6

Only RNA made by ____ is capped because guanylyl transferase is associated with the CTD of this polymerase

Answer 6

RNA Pol II

Question 7

What determines the 3’ end of an mRNA

Answer 7

The processing event of the addition of the poly A tail

Question 8

Poly A Polymerase

Answer 8

template-independent
requires 3’ OH after cleavage

Question 9

Why is the poly A tail made of adenosine as opposed to a different nucleotide?

Answer 9

Because most endonucleases don’t cleave between adenosine units

Question 10

Histone mRNA

Answer 10

3’ end has a self-complementary sequence
Stem Loop Binding Protein

Question 11

Prevalence of introns

Answer 11

Bacteria: not present
Yeast: present and small, not prevalent
Yeast mitochondria: many self splicing introns
Mammals: Common and large compared to exons

Question 12

What components of mammalian cells do not contain introns

Answer 12

mitochondria and histone mRNA

Question 13

Group I and II introns

Answer 13

self-splicing
require no additional proteins or ATP

Question 14

Spliceosomal introns

Answer 14

spliced by spliceosomes
most common
frequent in protein-coding regions

Question 15

tRNA modification

Answer 15

spliced by protein-based enzymes
primary transcript spliced by endonuclease
exons joined by ATP-dependent ligase

Question 16

Nuclear pre-mrna intron splicing mechanism

Answer 16

Spliceosome, internal 2’ OH provides free OH group

Question 17

Group I self-splicing intron splicing mechanism

Answer 17

guanine nucleotide provides 3’ OH
more common than group II
found in organelles and nucleus in lower eukaryotes

Question 18

Group II self-splicing intron splicing mechanism

Answer 18

internal 2’ OH provides free OH
Found in mitochondria, chloroplast, tRNA, and pre-mRNA

Question 19

What intron sequences are conserved during splicing?

Answer 19

Small regions immediately adjacent to splice sites

Question 20

Spliceosomes are made of

Answer 20

snRNPs

Question 21

snRNPs are made of

Answer 21

snRNAs

Question 22

Step 1 of splicing mechanism

Answer 22

2’ hydroxyl of branch-point A attacks bond at upstream end of intron, forming a loop, and leaving a 3’ hydroxyl upstream

Question 23

Conformational change that occurs during step 1 of splicing mechanism

Answer 23

transesterification

Question 24

Is ATP required for step 1 of splicing mechanism

Answer 24

No

Question 25

Step 2 of splicing mechanism

Answer 25

The free 3' OH of the upstream exon can now attack bond at downstream end of intron

Question 26

What is the structure that is formed during the splicing mechanism

Answer 26

lariat

Question 27

Step 3 of splicing mechanism

Answer 27

The intron is excised as a lariat and the upstream and downstream exons are covalently spliced together by a new phosphodiester bond

Question 28

rRNA processing by Pol I

Answer 28

a series of cuts by endonucleases occur in the nucleolus to convert precursor into 3 products that become part of each ribosome

Question 29

T/F There is no splicing involved in rRNA processing

Answer 29

true

Question 30

rRNA processing requires

Answer 30

snoRNAs: small nucleolar RNAs

Question 31

3' end of tRNA are modified to be

Answer 31

CCA-3'

Question 32

What is the purpose of the modified end of tRNA

Answer 32

to provide a binding site for amino acids

Question 33

tRNA modifications

Answer 33

1. CCA-3' end 2. Addition of methyl and isopentenyl groups. Methylation of 2' OH in ribose 3. Conversion of specific uracil bases to uracil-adjacent structures

Question 34

Transport of mature RNA out of the nucleus is facilitated by

Answer 34

nuclear pores

Question 35

rRNA is transported out of the nucleus as

Answer 35

pre-ribosomal particles