Primerano - Transcription and RNA Processing (I/II) Flashcards
What is the role of Ribosomal RNA (rRNA)?
WIth ribosomal proteins, make up the ribosome organelle that translate the mRNA
Transfer RNA (tRNA)
Shuttles Amino Acids to ribosomes during translation
Messenger RNA (mRNA)
Encodes amino acid sequence of a polypeptide (RNA polymerase makes from ssDNA to leave the nucleus towards the ribosome for transcription)
Small Nuclear RNA (snRNA)
With proteins, forms complexes that are used in RNA processing in eukaryotes
What is the role and impact of non-standard bases in RNA?
~ 10% of all bases in tRNA modified, these change base pairing properties and stabilize hairpin loops
What are the main two differences between transcription in prokaryotes and eukaryotes?
In eukaryotes transcription is temporally and spatially separated
What is the difference between housekeeping and tissue specific genes?
Housekeeping are uniform throughout an organism, tissue specific are localized to micro environments for a specific purpose–e.g. RBCs have Hb, other’s don’t
What is a major requirement in eukaryotic transcriptional initiation?
GTFs (General Transcription Factors)
What is the major role of TFII-H?
Helicase and kinase activity
What leads to dissociation of Pol-II from the preinitiation complex?
What does this signal the start of?
Phosphorylation of 5th serine residue by TF2-H
Initiation of transcription
What does RNA Pol I transcribe?
What processes it?
Single gene, precursor of large ribosomal rRNA (18S, 28S, +5.8S)
Cleaved by Rnases
What does RNA Pol II transcribe?
What is unique about RNA Pol II?
All mRNA genes, as well as microRNA precursors and most snRNA involved in splicing.
Only Pol II transcripts are poly-adenylated
What does RNA Pol III transcribe?
What recruits Pol III?
Small genes like tRNA, U6 snRNA, and 5S rRNA gene
Transcription Factors bind downstream to recruit Pol III (each listed above has different TFIII’s)
What is a eukaryotic promoter?
Where is it located?
What do they contain?
Regulatory region of DNA providing control point for regulated gene transcription
Located upstream (toward 5’ region)
Contain transcription factors
What is the difference between prokaryotic and eukaryotic promoters?
Prokaryotes: Two short sequences -10, -35 (upstream); -10 = Pribnow Box (TATAAT; -35 = TTGACA
Eukaryotes: Diverse, usually upstream and more regulated, many contain TATA Box
How is pre-rRNA processed in eukaryotes? Where does this occur?
Pre-rRNA is processed via cleavages, processing occurs in the nucleolus, which acts as a ribosomal factory
What molecules participate in cleavage and are capable of hydrogen bonding with pre-rRNA?
Small Nucleolar RNA (snoRNA) and Small Nucleolar Ribonucleoparticles (snoRNPs)
What is tRNA originally transcribed as?
What process occurs at the 3’ end?
pre-tRNA
RNAse P (RNA-protein complex) cleaves the 3’ end, and CCA end is added (site of AA attachment)
What are methods of regulation for RNA reactions?
Hydrogen Bonding, Methylation, and Chemical Conversion of Bases (e.g. uridine to pseudouridine)
Describe the process of capping.
What is unique about this linkage?
What role does the cap play?
Addition of 7-methyl guanidine to 5’ end
Rare 5’-5’ phosphodiester linkage–stabilizing factor due to long half life
Stabilize mRNA, helps align with ribosome
Describe the process of tailing.
An area rich in what bond pairs is downstream to the site?
What is the role of the Endonuclease?
What does capping attract?
Adds 10-30 bases upstream at the AAUAAA signal
G-U rich element is downstream
Cleaves the chain and poly-A-polymerase adds a poly-A tail of ~ 200 bases
Poly-A tail attracted to phosphorylated CTD of RNA Polymerase
What is the first step in splicing?
What does this leave?
What is joined following this?
What is formed?
Cleavage of 5’ splice site, leaves exon with free 3’ end
The 5’ end is joined with the 2’ hydroxyl of adenine that is near the 3’ end of the intron–forming the lariat
What is the second step of splicing?
Once this occurs, what happens next?
Cleavage of the 3’ site releases the lariat
The 3’ exon is joined with the 5’ exon
Where does splicing take place?
What are their subunits?
Spliceosomes
5 types of snRNA to form snRNPs
