Transcription 2 - RNA Processing Flashcards
What are the three ways that RNA is processed?
- 5’ capping
- 3’ poly-A tails
- mRna editing (alternative splicing)
Role of 5’ cap in RNA processing
- Protects mRNA from exonuclease activity as it leaves the nucleus
- Binds to specific cap-binding protein
- Particpates in binding to the ribosome to initiate translation
Describe the structure of the 5’ cap
7-methyguanosine attached to 5’ nucleotide via a triphophosphate linkage
2’-hydroxyls of first and second nucleotides often methylated.
What is the role of poly-A tail?
- Protects the RNA from degradation once it leaves the nucleus
- involed in RNA transport
T/F: Poly A tail is encoded in the genome
False. Product of enzyme activity triggered by the polyadenylation signal (AAUAAA) which is encoded
Describe the four (4) classes of introns
Group 1 introns
Group 2 introns
Spliceosomal introns
tRNA introns
T/F: Group 1 and 2 introns require ATP
False. They are autocatalytic.
What are Isoforms?
Two or more functionally similar proteins that have a similar but not identical amino acid sequence and are either encoded by different genes or by RNA transcripts from the same gene which have had different exons removed.
What to reactions do ribozymes catalyze?
Transesterification and hydrolysis of phosphodiester bonds
Define and differentiate between the terms primary transcript, hnRNA, pre-mRNA and mRNA.
primary transcript - immediate product of transcription containing introns and exons and 5’cap
hnRNA - heterogeneous nuclear rna is a collective term for the unprocessed mRNA (pre-mRNA) molecules in the nucleus.
pre-mRNA - unprocessed mRNA
mRNA - mature mRNA after all 3 steps of processing
List the steps involved in the maturation of RNA in a eukaryotic cell.
- 5’ capping
- 3’ tailing
- Cleavage
- Polyadenylation
- Splicing
Define the terms intron and exon.
Intron - coding region of gene
Exon - noncoding region of gene
Define the terms “spliceosomal introns” and “spliceosomes.”
Spliceosomal intron - non-coding sequences excised from pre-mRNAs by a special complex called spliceosome during mRNA splicing.
Spliceosome - large RNA-protein complex that catalyses the removal of spliceosomal intron from pre-mRNA
Outline the splicing mechanism in group I introns.
Outline the splicing mechanism in group II introns.
Outline the splicing mechanism in spliceosomes.
Compare and contrast the splicing mechanisms in group I, II and spliceosomal introns.
Describe the distinctive structure of the 3’ end of a eukaryotic mRNA and explain how it is added.
- Recognition - of the polyadenylation sequence by PAP
- Cleavage - of the transcript by PAP endonuclease activity
- Addition of A residues to free 3’ OH by PAP
Name the enzymes involved in “tailing.”
RNAP II
Polyadenylate polymerase
List important steps in mRNA maturation and when they occur.
- 5’ capping after first 20-30 ntds
- 3’ poly-A tails after AAUAAA sequence
- mRna editing (alternative splicing)
Describe how differential RNA processing generates multiple products from a single gene.
Discuss the concept of RNA stability
Describe the 3 steps of the 5’ capping process
Hydrolysis of the 5’ phosphate
Addition of GTP
Guanosine methylation
