Chapter 8: RNA General structure of RNA Process of transcription in prokaryotes and eukaryotes Other functions of RNA, small nuclear RNAs (snRNAs), micro-RNAs (miRNAs) and small interfering RNAs (siRNAs)
Announcements Quiz 6 Presentation on Wed. from first group on journal article Due today In-Class on DNA Homework chapter 7 and 8
DNA codes for proteins Once the DNA sequence for humans was known, what else can be determined?? If E. coli has 3200 genes, Drosophila has 13,600 genes, then humans must have….
The results of the GeneSweep pool Lee Rowen from Institute for Systems Biology
The pulse-chase experiment How is information transferred from DNA to proteins? What was determined from this?
What do you know about RNA?
Different classes of RNA Messenger RNA Functional RNA (found in all cells) tRNA rRNA Other Functional RNAs Small nuclear RNAs MicroRNAs Small interfering RNAs
Which strand of DNA? Only one strand is template Varies with the gene
Overview of Transcription
Prokaryotes vs Eukaryotes
Transcription in prokaryotes
Transcription in prokaryotes: Initiation Composed of five subunits plus sigma factor Sigma factor binds to the promoter region
Transcription in prokaryotes: Elongation and termination
Transcription in prokaryotes: Termination
Transcription in eukaryotes More complex….more genes Many types of RNA Polymerase Cell architecture different RNA processing
Initiation in eukaryotes TATA-binding protein binds to TATA region Other GTFs bind and attract RNA Polymerase II
Cotranscriptional processing 5’ cap made of 7-methylguanosine residues
Cotranscriptional processing Conserved sequence (AAUAAA) signals an enzyme to cut RNA Poly(A) tail is added to the 3’ end of transcript
Cotranscriptional processing Coding regions (exons) are spliced from non-coding regions (introns)
Splicing occurs at conserved regions
Spliceosome assembly Requires snRNPs (protein and snRNAs)
Benefits of alternative splicing?
Self splicing introns? 1981 Tom Cech identified rRNA from protozoan that could excise own intron RNA that are enzymes?? What does this mean about the function of RNA?
Genes code for proteins…right? 1993 Ambros discovered new gene (lin-4 gene) Does not code for a protein! microRNAs are discovered!
Silence genes with dsRNA? Inserted dsRNA into embryos Results suggested gene silencing occurred!
What happens if you insert a transgene? Transgene is….? What did they expect to see? What did they actually see? Cosuppression!
How can transgene result in dsRNA?
More evidence of gene silencing Viral gene inserted into plants Plant is resistant to viral infection How??
RNA interference (RNAi) Model for eliminating mRNA in a cell
New Roles for RNA! snRNAs miRNAs and siRNAs Gene silencing What other applications are possible with miRNAs and siRNAs?