16 Questions
What is the function of the 5’ cap region of eukaryotic mRNAs?
Align on the ribosomes during protein synthesis
What is the structure added to the 5’ end of the transcript during capping?
7 methylguanozin cap (m7G)
Which enzyme is responsible for adding the Poly-A tail to the 3 ’end of eukaryotic mRNAs?
Poly-A polymerase
How is capping initiated in eukaryotic mRNA processing?
Addition of a GTP in reverse orientation to the 5’ end of the mRNA forming a 5’-to-5’ linkage
Which process adds a poly-A tail to the 3' end of most eukaryotic mRNAs?
Polyadenylation
What regulates translation and mRNA stability by protecting mRNA from 3'-exonuclease degradation?
Polyadenylation signals
Which sequence do polyadenylation signals in mammals consist of?
AAUAAA
What cleaves the pre-mRNA at a CA sequence, located downstream of AAUAAA, during polyadenylation?
Endonuclease
What is the removal of introns from pre-mRNAs to produce mature mRNAs called?
Splicing
When were introns discovered unexpectedly?
1977
What was developed to study splicing by transcribing intron-containing genes in vitro and observing splicing reactions in mammalian cell extracts?
In vitro systems
Where does the first step of splicing take place, forming a lariat-like structure?
Branch point
What are recognized by the splicing apparatus in pre-mRNAs?
Consensus sequences at the 5' and 3' splice sites and at the branch point
What are large RNA-protein complexes called, in which splicing occurs?
Spliceosomes
Which type of RNA is involved in spliceosomes?
snRNA
Which step involves the excision of the intron and ligation of the two exons during splicing?
Second step
Study Notes
- Polyadenylation is a processing reaction that adds a poly-A tail to the 3' end of most eukaryotic mRNAs
- Poly-A tails regulate translation and mRNA stability by protecting mRNA from 3'-exonuclease degradation
- Polyadenylation signals in mammals consist of a hexanucleotide AAUAAA sequence and upstream and downstream GU rich elements
- Endonuclease cleaves the pre-mRNA at a CA sequence, located downstream of AAUAAA, and polymerase adds a poly-A tail of about 200 adenines
- Splicing is the removal of introns from pre-mRNAs to produce mature mRNAs
- Introns were discovered unexpectedly in 1977 and research focused on understanding splicing mechanisms
- In vitro systems were developed to study splicing by transcribing intron-containing genes in vitro and observing splicing reactions in mammalian cell extracts
- Splicing takes place in two steps: first, the pre-mRNA is cleaved and the intron is joined to an adenine near its 3' end, forming a lariat-like structure; second, the intron is excised and the two exons are ligated
- Pre-mRNAs contain consensus sequences at the 5' and 3' splice sites and at the branch point, which are recognized by the splicing apparatus
- Splicing occurs in large RNA-protein complexes called spliceosomes, which consist of 5 types of snRNAs and 6-10 protein molecules.
Test your knowledge on mRNA processing, focusing on the capping modification of the 5’ end of mRNA and its function in eukaryotic mRNAs. Explore the significance of the 5’ cap region in protein synthesis and more.
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