6a- RNA processing Flashcards
what is methyl-guanosine capped and poly-a-tailed?
mRNA
is mRNA monocistronic?
yes, only 1 coding region
what end of mRNA has 200 adenosine residues added to it after transcription?
3’ end of mRNA
what post-transcriptional processes can occur to tRNA?
1)methylation 2)pseudorylation
what is pseudorylation?
isomerizing specific uridine residues in RNA
what is pseudorine?
the C-glycoside isomer of the nucleoside uridine
what is a nucleoside?
purine/pyrimidine + sugar (no phosphates)
where are eukaryotic ribosomes made?
nucleolus
cleavage,methylation and ribosome production are post transcriptional processes of what?
rRNA
what is rRNA synthesized from in eukaryotes?
45S precursor in eukaryotes
what splices out introns?
spliceosomes
how can you produce variant proteins from a single gene sequence?
alternative splicing
what type of structure is essential for mRNA stability?
m7 G cap structure
does mRNA processing occur in eukaryotes and prokaryotes?
no only in eukaryotes
what determines mRNA’s half life in the cytoplasm?
its poly-A tail
is bacterial mRNA polycistronic?
yes
define polycistronic:
a genetic unit that encodes several polypeptides
what region of mRNA is targeted by signals?
3’ UTR
What eukaryotic mRNA processing can occur?
5’ cap and 3’ polyadenosine tail
what does the 5’ cap consist of?
of a guanine nucleotide connected to mRNA via an unusual 5′ to 5′ triphosphate linkage
is the guanine in the 5’ cap methylated?
yes it is methylated on the 7 position directly after capping in vivo by a methyltransferase
what functions does the 5’ cap have? (4)
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.
what is the process of adding a poly (A) tail to mRNA?
Polyadenylation
what is formed by a stretch of RNA that has only adenine bases
poly-A tail
is polyadenosine enoded in the gene?
No, polyadenosine is added posttranscriptionally and is not encoded in the gene.
what is polyadenylation part of the process of?
part of the process that produces mature messenger RNA (mRNA) for translation. It, therefore, forms part of the larger process of gene expression.
Nuclear export, translation, and stability of mRNA are all functions of what?
Poly (A) tail
what are the poly(A) tail functions? (4)
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.
