BIO 151 1st Edition Lecture 19 Outline of Last Lecture - Proteino Monomers of amino acids- RNA codingo tRNAo CodonOutline of Current Lecture - Transfer RNA- Wobble Base flexibility- Ribosomes as the assembler- Translation- Elongation phase- Termination- Why transcribe RNACurrent Lecture- Transfer RNA (tRNA)- “The adapter” o Cell finds way to match amino acid with mRNAo mRNA: 5’ CGA 3’ (mRNA codon) Arg (Amino acid)o Jobs:  At 3’ end, tRNA forms bond with amino acid Anticodon: RNA bases that match codon - Order of bases reversed with respect to codon- Complements codonThese 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. Links codon with amino acids- How do tRNA and Amino acids meet/o Amino acids + tRNAo Matchmakers called amino acyl-tRNA synthases 20 of the enzymes, 1 for each amino acido A tRNA to amino acid matchmaker Example: arginyl-tRNA synthase: only fits arginine (an amino acid); only accepts tRNA with anticodon for arginine Process has specificity Process requires energy: catalytic domain: place where this rxn takes place on enzyme. ATP  AMP + 2P- tRNA shortageso 20 amino acids, 20 amino-acyl tRNA synthases,  1 acyl tRNA synthase for 1 amino acid- Will accept tRNA with anticodon for that Amino acido 61 mRNA codons for Amino acid Need 61 anticodons on 61 tRNAso Problem: cell only has 45 RNAs and therefore only 45 anticodonso To solve problem: Wobble base flexibility in an otherwise highly specific process Wobble base of anticodon (5’ most base)- U at wobble position can pair with A or G at 3’ of codon Also works in reverse: 5’ most U at mRNA can complement A or G on anticodon- The assembler: Ribosomeo Ribosome: large and small subunit, each made of protein and ribosomal RNA (rRNA)- RNA does most of the worko lots of ribosomes in cell-rRNA most abundant cellular RNA Amino acyl-tRNA binding site (A site): tRNA with amino acid enters Large subunit: “top” Small subunit: “bottom” Peptidyl-tRNA biding site (P site) : tRNA with growing peptide bonds Exit site (E site): empty tRNA exits Exit Tunnel mRNA biding site: 5’ cap, modified guanine- How to build a peptideo Initiation: small ribosome subunit binds mRNA  Small and large ribosome subunits come together- Proteins called initiation factors bring the complex togethero Elongation: Charged tRNA enters translation complex at A site New amino acid is added to peptide chain at P site Empty tRNA exits translation complex at E site ****Repeato Termination: stop codon on mRNA causes release of polypeptide and ribosome complex disassembly - Initiation of translationo Small ribosomal subunit binds to mRNA  AUG: initiator codon has complement of AUG mRNA binding site at 5’ side Hydrolysis of GTP to GDP +Pio First tRNA is the only one that enters at P site, other tRNA enter at A site- Elongation phase: repeatedo Amino acids added to 3’ of growing peptide chaino Steps 1 and 3 require GTP Hydrolysis o 1. Codon recognition: in RNA codon facing A site is matched to tRNA carrying amino acido 2. Peptide Bond Formation: rRNA of large subunit forms peptide bond between amino group of new amino acid in H site and carboxyl end of polypeptide at P site polypeptide removed from tRNA in P site and is now attached to tRNA in A siteo 3. Translocation: mRNA slides over Empty tRNA in P site goes to E site and is released tRNA in A goes to P site ***grows from N terminus (amino) to C terminus (carboxyl- Termination: o Ribosome reaches mRNA stop codon in A siteo Release factor: binds A site; stop codon is the release factor not tRNA; looks like tRNA but isn’to Peptide bond to tRNA in P site hydrolyzed, polypeptide released Free polypeptide chaino Ribosomal subunit released- Why transcribe RNA?o Polyribosomes enhance protein production Multiple peptides from 1 mRNAo Start at 5’ end  goes  next RNA comes in o If cell transcribes RNA can use multiple