Transcript ppt
Functions of RNA • mRNA (messenger)- instructions protein • tRNA (transfer) - carriers that match amino acids to codons during translation • rRNA (ribosomal)- part of the ribosomesribosomes are RNA plus proteins • snRNA's (small nuclear) - part of spliceosomes- that edit mRNA's • siRNA’s (small interfering) control gene expression. The “central dogma” of molecular biology DNA replication transcription mRNA translation protein What is a “gene”? • “The genetic information that codes for a particular kind of protein”. However… • Some “genes” code for RNA molecules that have other functions (are not mRNA) • Some “genetic elements” are never transcribed into RNA or translated but still do important things, like control gene transcription Transcription • Synthesis of RNA using DNA as a pattern • Promoter sequence at beginning and terminator sequence at end of transcription unit (why not call it a gene?) • RNA polymerases- (3 different ones in eukaryotes) • Only template strand of DNA is transcribed Transcription (see fig 12.5 in Brooker) Promotor RNA polymerase Terminator Transcription unit “raw” RNA transcript mRNA processing in eukaryotes • Pre-mRNA (the raw transcript) is modified before leaving nucleus • GTP cap and poly-A tail (a long string of adenosines) are added to 5’ and 3’ ends mRNA processing, continued • Non-coding introns are removed and the remaining exons are spliced together. Correspondence between exons and protein domains Translation (protein synthesis) • mRNA has the pattern (the codons) • tRNA’s (transfer RNA) deliver the amino acids and match anticodon to codon • Ribosomes are where this happens. Catalyze formation of the peptide bonds. • Aminoacyl tRNA synthetases reload the tRNA’s with matching amino acids Three different representations of tRNA molecules Different tRNA for each kind of amino acid Anticodon “Activating enzymes” (aminoacyl-tRNAsynthetases) load each amino acid on it’s correct tRNA molecule. Requires ATP Different synthetases for each kind of tRNA & amino acid Ribosome E is for “Exit”site E,P, and A are Binding sites for three tRNA molecules A is for Amino acid +tRNA binding site P is for Peptide+tRNA binding site The initiation of translation The elongation cycle of translation The termination of translation Polyribosomes Coupled transcription and translation in bacteria A summary of transcription and translation in a eukaryotic cell