RNA processing and translation Flashcards
(32 cards)
Conversion of primary transcript into
mature mRNA
Occurs primarily in eukaryotes
Conversion of primary transcript into
mature mRNA localised in
nucleus
RNA processing achieves three things:
Removal of introns
Addition of a 5’ cap
Addition of a 3’ tail
This signals the mRNA is
ready to move out of the nucleus and
may control its lifespan in the cytoplasm
5’ Capping involve the addition of
a methylated-guanosine (7-methyl G) is
linked to the phosphates at the 5’ end of the mRNA.
Addition of poly-A tail
at 3’ end of the mRNA
5’ Capping is mediated by
guanylyl transferase in the capping enzyme complex
Functions of 5’ capping (PST)
- Protects against degradation by ribonucleases and 5’ exonucleases
- Serves as recognition site for ribosomes (initiation factors)
- Transports mRNA from nucleus to cytoplasm
what attach poly(A) generated from ATP
Poly(A)polymerase and cleavage &
polyadenylation specificity factor (CPSF)
Functions pf poly a tai; EP
i. Ensuring efficient translation of the mRNA
ii. Provide stability of the mRNA during
transportation out of the nucleus.
Highly regulated and vital in the creation of stable and mature messenger RNA able
to undergo translation during protein synthesis
These modifications (5’ cap and 3’ end) share several functions (fph)
◦ facilitate the export of mRNA to the cytoplasm
◦ protect mRNA from hydrolytic enzymes
◦ help ribosomes attach to the 5’ end
Removal of introns involves
a complicated “molecular device” called a
spliceosome that involves protein and RNA (like a ribosome).
The 3’ end of a eukaryotic mRNA
is trimmed and cleaved 15-20 nucleotides past AAUAAA
Eukaryotic genes often contain intervening sequencings (introns)
that separate the exons and must be removed for proper protein translation to occur.
Splicing allows an increase in
the information content of a genome due to
alternative splicing products that produce novel proteins.
Performed by
spliceosomes (large RNA-protein complex
made of small nuclear ribonucleoproteins (snRNP)
Recognize exon-intron
boundaries and splice exons
together by
transesterification reactions
The 5′ splice site at the 5′ (left) end of the intron includes
the consensus sequence GU
The 3′ splice site at the 3′ (right) end of the intron includes
the consensus sequence AG.
The GU-AG rule describes
the requirement for these constant dinucleotides at the first two and last two positions of introns in pre-mRNAs.
Why splice?
more than one mRNA can be made from
the same gene.
The same pre-mRNA can be
spliced in three different ways, depending on which exons are kept
Pre-mRNAs undergo three steps before translation
5’ Capping, polyadenylation, and splicing.
