Transcription and Post Transcription 2B part 2 Flashcards
5’ cap (4)
a modified guanosine triphosphate added to the 5’ UTR end of the mRNA
acts as the binding site for ribosomes
protect from 5’-3’ exonuclease
5’-5’ triphosphate bridge forms by the addition of 7-methylgaunosine triphosphate to the 5’ carbon of the first nucleotide of mRNA.
Poly A tail
a long string go adenine nucleotides added to the 3’ end of the mRNA by Pol-A polymerase to protect the mRNA from being degraded (from 3’-5’ exonuclease) and incense translational efficient (influence how ribosomes get docked onto 5’UTR)
5’UTR and 3’ UTR
what they do
regulate mRNA stability and translational efficiency
5’ UTR (3)
what it has
+ in prokaryotes/ eukaryotes
contain a ribosome binding site that function in translational initiation
Shine Dalgarno sequence in prokaryotes
Kozak box sequence in eukaryotes
The open reading frame
includes
the region of mRNA that is translated and includes the start and stop codons at the borders and utr
UTRs are
not translated
3’ UTR cleavage (2)
+what is after cleavage on 3’ side?
polyadenylation signal in DNA gets translated into RNA in the 3’UTR which tells CPSF to cleave. Poly A then comes to add tail
3 steps of mRNA maturation that happens in nucleus
5’ cap
Poly A tail
intron splicing
removal of introns generate an….
open reading frame consist of a continuous stretch of codons and UTRs
If introns are not spliced out then….
ribosome make wrong amino acid and produce non functional proteins
so what is going out of nucleus to cytoplasm for translation?
5’ cap-5’UTR-protein coding sequence all exons-3’UTR-Poly A tail
splicesome (2)
made up of 5 noncoding RNAs (SnRNA) complied to several proteins to form a ribonucleoprotein
need ATP to function (hydrolysis)
How are intron spliced? (4)
- splice some binds to intron-exon junctions
- Loop intron out of the pre-mRNA bringing axons closer together (use to be far away)
- Clip the intron at each exon boundary releasing the lariat structure
- join the adjacent axons together by ligating them
Alternative splicing (4)
generating different proteins/mrna from one gene
dramatically increases the number and variety of proteins that can be encoded by the genome.
In eukaryotes, we are able to generate a maximum number of protein from minimum number of genes
different isoforms are made in different tissues from the same gene producing tissue specific phenotypes
isoforms
proteins that are similar to each other and perform similar roles within cells
Transcriptional regulation
control of mRNA synthesis
Transcriptional rate depends on
the speed of transcriptional initiation (Everything assembled on promotor)
Posttranscriptional regulation
processing of mRNA which affect its stability and translational efficiency
stronger promotor strength+outcome (2)
more mRNA been made, everything get on promotor a lot faster
pale blue eyes vs dark blue eye
longer poly A tail
more stable
stability of mRNA depends on
presence of 5’ cap and length of poly A tail
the expression level of a specific gene depends on (3)
abundance of mRNA, nucleotide sequence and its eventual translation
abundance of RNA depends on rate of (2)
synthesis (transcription) and degradation of mRNA (posttranscritptional)
Deletion of enhancer causes
Gene expression…bc…
decreased gene expression as RNA polymerase cannot initiate transcription
Removal of 5’cap causes
Gene expression…bc…
Decreased gene expression as mRNA degradation accelerated and less efficient in translation initiation
Deletion of TATA box causes
Gene expression…bc…
decreased gene expression because formation of transcriptional initial complex is hindered
inhibition of siRNA synthesis causes
Gene expression…bc…
increased gene expression as less mRNA degradation
