mRNA processing Flashcards
How is mRNA process before exiting out of the nucleus?
- Addition of a cap to the 5’ end.
- Addition of a poly-A tail to the 3’ end.
- Cutting out of introns from mRNA.
What’s is 5’ to 5’ linkage?
Nose??????????
In what type of cell is mRNA
Process?
In eukaryotic cell, because mRNA is in the nucleus and it has to be processed before exiting the cell.
- ( it is not required in prokaryotes because mRNA is in the cytoplasm already .
Function of the 5’ CAP?
- protection
- binding site for CAP binding proteins
(Cap binding protein attract ribosomes once it gets out of the nucleus)
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Steps in the addition to the CAP to the 5’ end?
- Guanine is added to the absolute 5’end. Via to the 5’ to 5’ linkage.
- That guanine and the first few nucleotide are then methylated.
Cap binding proteins then attached to it and atract ribosome once mRNA exits the nucleus.
Function of the poly A tail added to the 3’ end?
- Protection against nucleases.
- provide a lifespan
- allow mRNA - ribosomal attachment.
What are introns?
Junk sequence does not code for any gene.
Steps in adding a pol-A tail to the 3’ end.
Most genes are transcribed beyond coding sequence , the extra sequence will be cut off and the poly A tail will added.
- Poly-A polymerase detects a consensus sequence near the end of mRAN and cuts it 25 nucleotides downstream.
- poly-A polymerase adds 50-200 adenines to the cut end.
Is it good to have a mRNA STABLE FOREVER.
No, because condition might change. You might one a gene on now but maybe not in different condition.
Where introns might come from?
- rreoviruses
- trtansposomes
- mutated portions of a former exon.
Common propeerties of all introns ?
-Common in eukaryotes rare in prokaryotes
- the more complex the organism the more complex/ abundant the introns
-intron abundance and size vary per gene within species.
( some genes have no introns other have many)
Classification of introns?
Introns are classified by how they are removed.
- group 1 and group 2 introns ( in rRNA)
- Nuclear pre-mRNA introns
Group 1 and group 2 introns?
- Found in rRNA & few bacteria gene
- small
- uses guanosine to excise itself out. ( exon then glue)
Nuclear pre mRNA introns?
- Larger and more complex
- Require help from splicesomes in order to be removed
- Usually contain consensus sequence at the end that attract splicesosomes.( c.s in between intron/ exons)
Alternative splicing?
mRNA is spliced in different ways
- 100% of introns are removed.
- exons are differently Cut/Retained.
The more exons?
The more potential different isoforms..
Isoforms?
Different protein products from the same gene caused by alternate splicing
One gene can code for more than one protein. true or false?
Yes, one gene can code for more than one protein through alternate splicing.
Advantage of isoforms/ isoforms?
A way of coping more information in less space.
What happen right before mRNA is ready to exit the nucleus?
mRNA get scanned by the pos of the nucleus.
And will only exit with a cap, poly A tail and not introns.
What is mRNA EXPORTER.?
mRNP + (nuclear) Pore Complexes.
Function proteins called mRNP?
mRNP associate with processed mRNA and diret them to and through the nuclear pore.
Example of a disease caused because introns were never cut of and never mRNA never made it out of the cell?
Beta hemoglobin and thalassemia .
