Lecture 4- Eukaryotic Transcription continued and mRNA Exression Flashcards
What are the three main elements in Eukaryotic transcription?
- ) Multiple distinct RNA polymerases.
- ) Additional proteins (transcription factors) are needed for the initiation and regulation of transcription.
- ) Chromatin structure influences transcription activity.
What is the first modification of Eukaryotic mRNA? Where does it occur and why is it necessary? Describe what it is made off etc.
- Capping occurs at the 5’ end of the mRNA simultaneously during transcription elongation.
- Needed for mRNA stability to the cytoplasm for translation. Protects the mRNA from degradation.
- The 5’ Cap is called the 7-methylguanylate cap because it is a guanine with a methyl group attached to its 7’ end.
- It is bound by 5’-5’ triphosphate linkage.
Why are regions of templates of DNA unable to bind to regions of mature mRNA?
- The mature mRNA has the 5’ cap and 3’ poly A tail while DNA template strand does not.
- Also, the DNA template strand has the introns within while the mature mRNA has excised them out.
What is the specific order of pre-mRNA processing?
- ) Capping
- ) RNA splicing
- ) 3’ end formation
How are splice sites recognized in the pre-mRNA?
- There are specific consensus sequences that are found at the beginning and ends of the introns.
What structure does pre-mRNA splicing? What is it made out of?
- The spliceosome is what splices the introns out of pre-mRNA.
- The spliceosome is made up of RNA and proteins called snRPS (snRNA + proteins).
What are the specific functions of snRNA?
- ) To recognize the 5’ splice site and base site through base pairing recognition.
- ) To require ATP hydrolysis for stepwise assembly and RNA rearrangements that create the active catalytic site.
What are the steps in the splicing reaction?
- ) Branch site of 2’ OH group called the A site (found within the intron) found more towards the 3’ exon attacks the 5’ splice site creating a lariat. The 5’ exon is now free.
- ) The A site now attacks the 3’ splice site and an intron lariat is formed. Exons are joined together.
What is polyadenylation? What is the Poly-A tail consisted of?
- The addition of a Poly-A tail to a pre-mRNA which produces mature RNA.
- The Poly-A tail consists of a string of adenosine monophosphates.
What is the process of polyadenylation?
- The cleavage site is what determines the end of the pre-mRNA. It is located between an AAUAAA consensus sequence and a GU-rich region.
- An endonuclease cleaves this point that Poly-A Polymerase does polyadenylation and adds the poly A tail which is about 150-250 n.b. long.
Are RNA polymerase II mRNAs determined by the termination of transcription?
- No. Polyadenylation is the process.
How is an exoribonuclease involved in the termination of transcription and RNA polymerase? Eukaryotes.
- RNA polymerase II transcribes well passed the cleavage site to form the mRNA. pre-mRNA is cleaved at the 3’ end.
- As RNA Polymerase II transcribes past the cleave site and endoribonuclease attaches to the cleaved 5’ end and starts to degrade the extra RNA strand (which is not part of the pre-mRNA strand) until it reaches the RNA Polymerase II, then transcription is terminated.
How does the mature mRNA look?
5’ cap -> 5’ UTR -> coding region -> 3’ UTR -> Poly A tail
What molecules help with an export of the processed mature mRNA? Where are they deposited and where does it export from?
- Proteins are deposited on the mature mRNA.
- They deposit the mRNA from the nucleus to the cytoplasm.
Where do transcription and translation happen in both prokaryotes and eukaryotes; what are the steps?
- ) Prokaryotes:
- Both transcription and translation occur in the cytoplasm of the cell. Only in one area.
- There is no pre-mRNA only straight mRNA - ) Eukaryotes:
- Transcription happens in the nucleus
- Then pre-mRNA processing occurs (still in nucleus).
- Mature mRNA is then exited into the cytoplasm where it is then translated into proteins
