Gene Expression Flashcards
Transcription
DNA to RNA
Translation
RNA to protein
Initiation (transcription)
RNA polymerase binds to promoter
Elongation (transcription)
DNA helix unwinds and RNA polymerase adds nucleotides in the 5’ to 3’ direction
Termination (transcription)
Polymerase reaches terminator sequence
Processing (transcription)
Polyadenylation & splicing
Histidine decarboxylase
Enzyme responsible for the production of histamine
Diamine Oxidase
Terminates the action of histamine
Initiation and pre-initiation complex
- TF2D binds to the TATA sequence:
-This causes other transcriptional factors to bind
-This initiates the formation of the pre-initiation complex - The pre-initiation complex brings RNA pol II to the promoter region (Transcription initiation start site)
-PIC also denatures DNA (DNA has to unwind in order to use one strand as the template)
-The PIC then positions the DNA template to the RNA pol II active site
Why does RNA pol II need the pre-initiation complex?
RNA pol II does not hav enough energy on its own to start transcription, it needs the TF’s (on PIC) to help bind and unwind DNA
Why do we need capping in transcription?
The RNA transcript is single stranded. Thus, it is less stable so the 5’ cap is added to keep it from degradation
How capping works:
- The C terminus of RNA pol II is phosphorylated by kinases
- Once the phosphate groups are added, the capping enzymes come in and add the cap to the 5’ end of RNA
- Transcription can the proceed
Polyadenylation
- On the pre-mRNA there is a PolyA signal
- The PolyA signal is recognized by the CPSF enzyme
- CPSF binds to the signal and initiates the cleavage event of about 20-30 nucleotides downstream
- The cleavage event results in a new 3’ hydroxyl. From the 3’ hydroxyl, the PAP enzyme comes in and adds all the A’s. Once the tail reaches 200-300 A’s, the PAP disengages and now we have the Poly A tail.
(If the poly A tail reaches a certain length it signals the mRNA for degradation)
CPSF
Cleavage and polyadenylation specificity factor
PAP
Polyadenylate polymerase
Splicing
This is the last stage before leaving the nucleus
1. The SnRNPS’S BIND TO THE 3’ AND 5’ end of the intron
2. They cleave at the 5’ and the 3’
3. The Introns are looped out and the exons are joined together
SnRNP
the RNA of spliceosomes. They recognize the split junctions between the introns and the exons.
Initiation (Translation)
Binding to ribosome at the 5’ cap
Elongation (Translation)
tRNA add amino acids to the growing chain
Termination (Translation)
Ribosome reaches a stop codon
Processing (Translation)
(critical for cell signalling)
modification or addition of a functional group- glycosylation, acylation, methylation
Initiation (Ternary complex)
- The ternary complex binds to the 40s subunit
- Once the ternary complex binds to the 40s subunit, eIF4E binds to the 40s subunit. eIF4E binds to the 5’ cap. This is how the ribosome finds the mRNA.
The Ternary Complex
Is made up of GTP, EIF2 (INITIATION FACTOR), tRNA with methionine (starting amino acids)- translation cannot occur without the first amino acid
Initiation (scanning)
translation
-the ribosome binds to the 5’ end of mRNA
-right beside the 5’ end is the untranslated region (UTR)
-the complex scans through the UTR in order to find the start codon
-once at the start codon, a lot of the initial factors are released
-because of their release the 60s subunit can now join the 40s subunit
-scanning is an energy dependant process