RNA and RNA world-复旦《医用分子遗传学》课件.ppt

Transcription-the synthesis of RNA using DNA as a template. Four stages: Initiation, Elongation, Termination, Post-transcriptional modification  Similarities and Differences from Replication  Similarities Differences 5' →3' direction ?RNA polymerase instead many proteins involved of DNA polymerase initiation, elongation, ? no proofreading termination ? posttranscriptional transcription bubble modification starts and stops at ? 1 strand copied not 2 specific places ? not all copied Nt not dNt Terminology of Transcription (3') ACG GAA TAA TTA TGT TTA TCA CAA TTT AGA (5') + (plus) strand template strand (5') TGC CTT ATT AAT ACA AAT AGT GTT AAA TCT (3') -(minus) strand non-template strand coding strand (5') UGC CUU AUU AAU ACA AAU AGU GUU AAA UCU (3') RNA transcript  Upstream 5’ end vs. Downstream 3’ end Termination Rho (ρ)-dependent vs. ρ-independent ρ-Dependent Termination A hairpin forms if protein called ρis present, polymerase detaches Dissociation is somehow coupled to ATP hydrolysis RNA polymerases in Eukaryotes RNA polymerase I transcribes rRNA RNA polymerase II transcribes mRNA RNA polymerase III transcribes tRNA and other small RNAs. Animal RNA Polymerases Animal DNA-dependent RNA Polymerases Class α-amanitin sensitivity Major Products I Insensitive rRNA II Low Conc. (1-10 nM)