L7 RNA Processing Flashcards
What are the major types of cellular RNA?
The major cellular RNAs are:
* messenger RNA (mRNA)
* ribosomal RNA (rRNA)
* transfer RNA (tRNA)
* some small stable RNAs
mRNA is generally unstable and not clearly visible on gels.
What are the three main steps in eukaryotic mRNA processing?
Eukaryotic mRNA processing comprises three main steps:
* capping of the 5’ end
* removal of introns (pre-mRNA splicing)
* 3’ end processing (cleavage and polyadenylation)
Processing occurs in the nucleus, and functional mRNAs are exported to the cytoplasm for translation.
Where does mRNA occur?
In the nucleus.
What is the purpose of the cap and poly(A) tail in mRNA?
The cap and poly(A) tail protect the mRNA against degradation and promote translation.
What is the structure of the ‘m7G cap’ in eukaryotic mRNA?
The ‘m7G cap’ structure consists of a guanosine nucleotide added to the 5’ end of RNA pol II transcripts linked by a 5’-5’ triphosphate linkage and methylated.
True or False: Prokaryotic mRNAs are typically monocistronic. Give explanation.
False
Prokaryotic mRNAs are typically polycistronic, meaning a single mRNA can translate multiple proteins.
What are ‘split genes’ in eukaryotic cells?
‘Split genes’ refer to protein-coding sequences within genes that are typically discontinuous within the chromosomal DNA.
What are the splice site sequences recognized during pre-mRNA splicing?
The splice site sequences recognized are
* 5’ splice site sequence GU
* 3’ splice site sequence AG
* branchpoint A
These sequences are highly conserved.
What is the role of the spliceosome in pre-mRNA splicing?
The spliceosome is a large ribonucleoprotein (RNP) that mediates pre-mRNA splicing by removing introns and keeping exons.
Fill in the blank: Pre-mRNA splicing involves two _______ steps.
transesterification
What happens during the first step of pre-mRNA splicing?
In the first step, the 5’ exon is released, and the intron forms a lariat structure involving the branchpoint adenosine.
What is a ribozyme?
Enzymes with an RNA catalytic subunit.
What is the significance of self-splicing introns?
Self-splicing introns have restricted structures that align the exons together and are thought to have evolved into nuclear pre-mRNA splicing.
What is the function of snRNPs in the spliceosome?
snRNPs, or small nuclear RNPs, are the smaller RNA/protein complexes that assemble and disassemble to form active spliceosomes.
What is the typical outcome of eukaryotic mRNA after processing?
Eukaryotic mRNAs encode a single polypeptide, and the expression of functionally related genes is coordinately regulated.
