Transcription Flashcards
What is the molecular definition of a gene?
Genes are sequences of DNA that is transcribed into RNA
Genes can be DNA or RNA
There are two types of genes when transcribed; those RNA that is translated and RNA that is not translated
Compare RNA and DNA polymerase
RNA:
Ribonucleoside uses AUCG
Made 5’-3’ adding to 3’end
DNA template read from 3-5
Produces single strand RNA
DNA:
-Deoxyribonucleoside uses ATCG
Missing oxygen on 2’ end
Produces double strand DNA
**phosphodiester bonds are present in DNA/RNA
Does RNA polymerase require a primer
No because it uses other enzymes to initiate the transcription process
What are the steps for transcription
- Sigma factor binds to rna polymerase and looks for initiator sequence
- Unwinding of DNA, abortive transcription where a few RNA are synthesized and the RNA polymerase clamps down and sigma factor is released
- Elongation
- RNAP is released
Where are the promotor consensus sequence
Typically at -10 and -35
Why does RNA Transcript form loops
Because when RNA transcript leaves RNA polymerase can base pair to itself
Terminator Sequence
A strong hairpin formation pulls the RNA off of the DNA so that the DNA, RNA, and RNAP all release from each other
How are the initial modes of transcription different from its elongation mode
The initial mode is inefficient and occurs very slowly (abortive state) where as the elongation mode occurs rapidly
What are the characteristics of RNA termination
- Hairpin structure formed from C-G rich sequences
- AT rich sequences following the c-g
How do these termination signals dissociate from DNA
Disrupts the H-bonding between mRNA transcript and DNA
T/F, Translation can begin before transcription is complete for both Prokaryotes and Eukaryotes
False only prokaryotes
Why can’t Eukaryotes undergo translation before transcription is complete
Because transcription happens in the nucleus and it cannot leave the nucleus before the process is complete
Does Eukaryotic transcription have sigma factors
No they have transcription proteins which facilitates similar roles helping place RNAP at promoter
TATA BOX
promoter sequence that helps position RNAP II and tells it to start transcription
How are Eukaryotic RNAP II and Bacterial RNA different structurally
Bacterial RNAP has 5 subunits, EUkaryotic RNAP II has 12 RNAP II has special carboxyl terminal Domain (CTD)
Describe the initiation process of transcription
For initiation to begin E needs general transcription to begin:
1. TATA box basically tells RNAP II to get ready for transcription
2. The TATA box is recognized by the TBP (TATA binding protein)
3. All of these factors assemble on the promoter
4. TFIIH pries apart the helix using ATP and it also helps RNA polymerase II get away from the other factors so it can be transcribing by adding phosphate groups to its 3’ tail
Before the RNA can leave the nucleus it needs to undergo mRNA processing. What are the steps involved in this process
- Adding 5’ cap (made from guanine and meth)- protect the RNA from exonucleases
- Polyadenylation (Poly-A-tail)- made by an initial enzyme trimming the nucleotides and then a second enzyme comes and adds adenine tail
- Splicing introns have a short sequence that identifies them as non-coding sequences that will be cut out-
The splicing machine/lariat structure will cut the introns: - The adenine “branch-A” will attack the 5’ splice site
- the exon on 3’ and 5’ get attached and the lariat is degraded
**the 5’ intron will attach to 2’oh ribose of adenine
3’ end processing
Up until now we have had pre-mRNA. In order for a mature mRNA to leave the nucleus 3’end processing where the Poly-A-binding protein and cleavage, along with the poly-a-tail complete the mature mRNA
Why do we need cap and tail
Makes it more stable and prevents mRNA degradation after it leaves the nucleus
