eukaryotes rRNA synthesis occurs in nucleolus and is catalyzed by RNA

Eukaryotes rrna synthesis occurs in nucleolus and is

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eukaryotes, rRNA synthesis occurs in nucleolus and is catalyzed by RNA polymerase I TRANSFER RNAs amino acids attached to correct tRNA molecules by aminoacyl-tRNA synthetases tRNA required for translation of mRNA to amino acid sequence anticodon of each tRNA occurs within a loop near the middle of molecule and base pairs with the codon of mRNA o anticodon 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 tRNA 1 tRNA for each amino acid 3 tRNA binding sites on each ribosome: o A site binds the tRNA carrying the next amino acid to be added to the chain o P site binds tRNA to which the polypeptide is attached o E site binds the departing uncharged tRNA TRANSLATION Initiation Prokaryotes tRNA f met recognizes initiation codon AUG and initiates synthesis initiation begins with: o IF-2 and tRNA f met o mRNA molecule, 30S ribosomal subunit and IF-3 o shine dalgarno sequence AGGAGG o IF-2/ tRNA f met complex and mRNA/30S/IF-3 complex combine with each other and IF-1 to form complete 30S initiation complex o Addition of 50S subunit to 30S complex to produce 70S ribosome No promoter in translation, only transcription Eukaryotes Translation begins at first AUG
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Amino group on Met not formylated Initiation complex forms at 5’ terminus not shine-dalgarno/AUG translation site Elongation Binding of aminoacyl-tRNA to A site of the ribosome Transfer of growing polypeptide chain from tRNA in P site to tRNA in A site by formation of new peptide bond Translocation of ribosome along the mRNA to position the next codon in A site Termination Occur when termination codon enters A site on ribosome (UAA, UAG, UGA) When stop codon encountered, release factor RF binds to A site E. coli o RF-1 recognizes UAA and UAG o RF-2 recognizes UAA and UGA Eukaryotes o eRF recognizes all three Reaction releases polypeptide from tRNA molecule in P site and triggers translocation of free tRNA to E site Codon-tRNA Wobble position: the third position of the genetic code can change without the amino acid changing
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MUTATIONS Mutation : change in genetic material Mutant : organism that exhibits new phenotype resulting from mutation Point mutation : change at a specific site in a gene o Transition : replacement of purine with purine or pyrimidine with pyrimidine Caused by tautomeric shifts o Transversion : replacement of purine with pyrimidine Frameshift mutations : base pair additions or deletions that alter reading frame Nonsense mutations : mutations that produce chain-terminating triples Missense : mutations that change a triplet so it specifies a different amino acid Silent mutation : mutation that changes one codon but not the entire amino acid (wobble position) Spontaneous mutations: occur without known cause Induced mutation : result from exposure of organisms to mutagens Mutations by chemicals Nitrous acid
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  • Fall '13
  • DNA, RNA molecules, rna polymerase

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