6a- RNA processing

Question 1

what is methyl-guanosine capped and poly-a-tailed?

Answer 1

mRNA

Question 2

is mRNA monocistronic?

Answer 2

yes, only 1 coding region

Question 3

what end of mRNA has 200 adenosine residues added to it after transcription?

Answer 3

3’ end of mRNA

Question 4

what post-transcriptional processes can occur to tRNA?

Answer 4

1)methylation 2)pseudorylation

Question 5

what is pseudorylation?

Answer 5

isomerizing specific uridine residues in RNA

Question 6

what is pseudorine?

Answer 6

the C-glycoside isomer of the nucleoside uridine

Question 7

what is a nucleoside?

Answer 7

purine/pyrimidine + sugar (no phosphates)

Question 8

where are eukaryotic ribosomes made?

Answer 8

nucleolus

Question 9

cleavage,methylation and ribosome production are post transcriptional processes of what?

Answer 9

rRNA

Question 10

what is rRNA synthesized from in eukaryotes?

Answer 10

45S precursor in eukaryotes

Question 11

what splices out introns?

Answer 11

spliceosomes

Question 12

how can you produce variant proteins from a single gene sequence?

Answer 12

alternative splicing

Question 13

what type of structure is essential for mRNA stability?

Answer 13

m7 G cap structure

Question 14

does mRNA processing occur in eukaryotes and prokaryotes?

Answer 14

no only in eukaryotes

Question 15

what determines mRNA’s half life in the cytoplasm?

Answer 15

its poly-A tail

Question 16

is bacterial mRNA polycistronic?

Answer 16

yes

Question 17

define polycistronic:

Answer 17

a genetic unit that encodes several polypeptides

Question 18

what region of mRNA is targeted by signals?

Answer 18

3’ UTR

Question 19

What eukaryotic mRNA processing can occur?

Answer 19

5’ cap and 3’ polyadenosine tail

Question 20

what does the 5’ cap consist of?

Answer 20

of a guanine nucleotide connected to mRNA via an unusual 5′ to 5′ triphosphate linkage

Question 21

is the guanine in the 5’ cap methylated?

Answer 21

yes it is methylated on the 7 position directly after capping in vivo by a methyltransferase

Question 22

what functions does the 5’ cap have? (4)

Answer 22

1) Regulation of nuclear export
2) Prevention of degradation by exonucleases;
3) Promotion of translation (helps ribosome binding site)
4) Promotion of 5′ intron excision.

Question 23

what is the process of adding a poly (A) tail to mRNA?

Answer 23

Polyadenylation

Question 24

what is formed by a stretch of RNA that has only adenine bases

Answer 24

poly-A tail

Question 25

is polyadenosine enoded in the gene?

Answer 25

No, polyadenosine is added posttranscriptionally and is not encoded in the gene.

Question 26

what is polyadenylation part of the process of?

Answer 26

part of the process that produces mature messenger RNA (mRNA) for translation. It, therefore, forms part of the larger process of gene expression.

Question 27

Nuclear export, translation, and stability of mRNA are all functions of what?

Answer 27

Poly (A) tail

Question 28

what are the poly(A) tail functions? (4)

Answer 28

1) nuclear export through nuclear pores
2) translation and stability of mRNA (targets mRNA too)
3) the tail shortens over time and is slowly enzymatically degraded in the cytoplasm.