BIO 326R 1st Edition Lecture 12 Outline of Last Lecture I. InitiationII. ElongationIII. Terminationa. Rho independentb. Rho dependentIV. Side notes on transcriptionV. TranslationOutline of Current Lecture I. Translationa. componentsi. Ribosomesii. tRNAb. initiationc. elongationd. terminationCurrent LectureTranslation- transcription and translation are coupled- most antibiotics target translation- componentsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o ribosomes prokaryotes have a 50s and 30s subunit to make a 70s unit- s= Svedberg unit—how something moves in a viscous field 30s is composed of 16s rRNA and ~21 proteins 50s is composed of 23s rRNA, 5s rRNA and ~34 proteins Ribozyme= ribosome with enzymatic functiono tRNA transfer RNA that can attach an amino acid covalently to the 3’ end- if attached—charged tRNA- ~50 tRNA in E. coli Amino-acyl tRNA synthetase= proteins that attach amino acids to tRNA- 20 of these enzymes in a cell—one for each amino acid Proofreading capacity Wobble= same tRNA can pair with codons that differ by the last nucleotide- This is possible because usually several codons code for the same amino acid, and these codons differ only in the last nucleotide- Initiationo Recognize the start site AUG on mRNA, ATG on DNA Bacteria use n-formylmethionine Ribosome binds at a specific site upstream from the start site- Shine-Delgarno sequence= tells the ribosome where to beo Upstream from AUG by ~7-10 basepairso Must be highly consensus in gram + but can be low in gram–o 5’-AGGAGGU-3’o Can base pair with 16s rRNAo Consensus of SD determines gene expression Ribosome can’t bind as well to a weaker sequence, so it will not be as expressedo Steps of initiation 30s subunit and initiation factors find SD- tRNA with formylmethionine- GTP Ready to translate, so kicks off initiation factors- Elongationo Steps Binding of 2nd aminoacyl-tRNA- Enters bound to EF-Tu and GTPo Hydrolyze GTPo Helps find binding site- EF-Ts o Removes GDP and adds inorganic phosphate to make a new GTP Make a peptide bind between the two amino acids- Done by 23s rRNA ribozyme Translocation- Ribosome moves along mRNA 5’3’ to continue adding amino acidso Speed ~15 amino acids/second Same speed as transcription (45 nucleotides/minute- Shows that they are coupled Multiple ribosomes on a single mRNA- Looks like beads on a string Half life of RNA is only a few minutes, so it’s important to be able to makeseveral peptides at once- Terminationo Steps Look for stop codons (nonsense codons) in frame with AUG start codon- UGA, UAG, UAA- No tRNA has an anticodon for these A protein called release factor will interact with these codons instead to release the
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