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Cell Biology Test 2 Notes (aced the test and got 96%)

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Louisiana State University
Biological Sciences
BIOL 3090

Study Guide for Exam 2Starting with Lecture 10 on Feb 12 Page 127 in the new 6th edition 1Fig 417 is a good review for protein translation mRNA is translated into protein by the joint action of tRNA and the ribosome made of numerous proteins and 2 major rRNA molecules Base pairing occurs between tRNA anticodons and mRNA codons Formation of a peptide bond between the aminogroup N on the incoming aatRNA and the carboxyterminal C on the growing protein chain is catalyzed by one of the rRNAs The nucleotides read as triplets codon 6164 codons encode AA 3 stop codons UAA UGA UAGdegenerate amino acids can be specified by multiple codonsAUG encoding Met fMet in prokaryotes used as translation start codon on rare occasion GUGCUG may be used to encode MetThree possible reading frames sequence of codons from a start codon to a stop codon because read as tripletsRare UGA may code for Trp or Cys instead of STOP CUG may code for Thr instead of Leu UAAUAG may code for Gln instead of STOPGenetic code was deciphered using synthetic mRNAs A bacterial extract cell lysate was added to synthetic mRNAs AAACCC UUU and gave certain polypeptides Synthetic transcripts now have 2 different nucleotides with 3 distinct reading frames2tRNAs are good to know Figs 420a and b 7080 nucleotides longCodon and anticodon interaction is antiparallelStructure oAcceptor stem 3 CCA amino acid covalently attaches hereoD loopoAnticodon loop pairing goes on hereoVariable loopoTCG loopBacterial tRNAo3040 different tRNAs in bacteriastoSingle tRNA can recognize several codons using wobble base position 1 rdbase in tRNA anticodon pairs with 3 base in mrNA codono Nontraditional base pairing can occur between U and GoPS Inosine is the deaminated form of adenineEukaryotic tRNAo50100 different tRNAsoMore tRNAs than codons one codon can attach to several tRNAs cognate and still produce one AA 3Aminoacyl tRNA synthetases Figs 419Charged tRNA has proofreading function can recognize cognate tRNAs anticodons and other parts of the moleculeDepends on both positive interactions and the absence of negative interactionsIf it finds a wrong attachment catalyzes the removal of the AA 4The wobble base position Fig 421 how does this relate to the genetic code being redundant degenerate Whats that bad boy inosine doing in a tRNA Codon bound to anticodon parallel or antiparallel AntiparallelInosine can form nonstandard base pairs with A C and U It can recognize codons with these bases in the third positionInosinecontaining tRNAs are employed in the translation of the synonymous codons that specify a single AA5The eukaryotic ribosome its structure and its components lower portion of Fig 422 Machines nanoorganisms that read mRNA bind activated tRNAs and growing peptide chains and catalyze peptide bond formation 100200minuteComposed of LSU and SSUIntact functional ribosome contains 4 rRNAs and 83 ribosomal proteinsProkaryotic subunitso50S30S70So52 proteinsoEnzymatic function contributed to the LSU 23S rRNAEukaryotic subunitso60S40S80So83 proteinsorRNA LSU 28S 58S 5SorRNA SSU 18SrRNAs have conserved secondary and tertiary structurespeptidyl transferase activated Met at P site and alpha amino group on second AA in the A site react to form a peptide bond6Translation initiation in eukaryotes know the steps in initiation Dont have to memorize the names of the individual eIFs but should know what SSU m7G Kozaks AUG LSU ATP and GTP hydrolysis are doing Fig 424 Initiation StepsoStep 1 and 2 Formation of a preinitiation complex 40S subuniteIF3 associates with eIF1 andeF2GTP which is attached to MettRNAoStep 3 Scanning of the mRNA by the associated initiation complex leads to positioning of the small subunit and bound MettRNA at the start codonoStep 4 Association of the large subunit forms an 80S ribosome ready to translate the mRNA Two Ifs eIF2 and eIF5 are GTPbinding proteins whose bound GTP is hydrolyzed during initiation AUG is situated into the P site
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