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eukaryotes, rRNA synthesis occurs in nucleolus and is catalyzed by RNA polymerase ITRANSFER RNAsamino acids attached to correct tRNA molecules by aminoacyl-tRNA synthetasestRNA required for translation of mRNA to amino acid sequenceanticodon of each tRNA occurs within a loop near the middle of molecule and base pairs with the codon of mRNAoanticodon is backwards and upsite down… if written as “5’-AUG-3’” to find the codon it must be read 3’5’ : 5’–GUA-3’translated to mRNA: 5’-CAU-3’amino acid is covalently attached to 3’ end of tRNA1 tRNA for each amino acid3 tRNA binding sites on each ribosome:oA sitebinds the tRNA carrying the next amino acid to be added to the chainoP sitebinds tRNA to which the polypeptide is attachedoE sitebinds the departing uncharged tRNATRANSLATION Initiation ProkaryotestRNAfmetrecognizes initiation codon AUGand initiates synthesisinitiation begins with:oIF-2 and tRNAfmetomRNA molecule, 30S ribosomal subunit and IF-3oshine dalgarno sequence AGGAGGoIF-2/ tRNAfmet complex and mRNA/30S/IF-3 complex combine with each other and IF-1 to form complete 30S initiation complexoAddition of 50S subunit to 30S complex to produce 70S ribosomeNo promoter in translation, only transcriptionEukaryotes Translation begins at first AUG
Amino group on Met not formylatedInitiation complex forms at 5’ terminus not shine-dalgarno/AUG translation siteElongationBinding of aminoacyl-tRNA to A site of the ribosomeTransfer of growing polypeptide chain from tRNA in P site to tRNA in A site by formation of new peptide bondTranslocation of ribosome along the mRNA to position the next codon in A siteTerminationOccur when termination codon enters A site on ribosome (UAA, UAG, UGA) When stop codon encountered, release factor RF binds to A siteE. colioRF-1 recognizes UAA and UAGoRF-2 recognizes UAA and UGAEukaryotesoeRF recognizes all threeReaction releases polypeptide from tRNA molecule in P site and triggers translocation of free tRNA to E siteCodon-tRNA Wobble position: the third position of the genetic code can change without the amino acid changing
MUTATIONSMutation: change in genetic materialMutant: organism that exhibits new phenotype resulting from mutationPoint mutation: change at a specific site in a geneoTransition: replacement of purine with purine or pyrimidine with pyrimidineCaused by tautomeric shiftsoTransversion: replacement of purine with pyrimidine Frameshift mutations: base pair additions or deletions that alter reading frameNonsense mutations: mutations that produce chain-terminating triplesMissense: mutations that change a triplet so it specifies a different amino acidSilent mutation: mutation that changes one codon but not the entire amino acid (wobble position)Spontaneous mutations:occur without known causeInduced mutation: result from exposure of organisms to mutagensMutations by chemicalsNitrous acid