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Microbiology 251 Notes from page 340 to 351

by: Julianna Sickafus

Microbiology 251 Notes from page 340 to 351 MICRB 251

Marketplace > Pennsylvania State University > Microbiology > MICRB 251 > Microbiology 251 Notes from page 340 to 351
Julianna Sickafus
Penn State

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About this Document

Notes taken from book reading. If there seems to be a lot of interest in this kind of notes (instead of additional slide material), I will post all notes from class readings.
Class Notes
ribosome, tRNA, Codon, anticodon
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This 3 page Class Notes was uploaded by Julianna Sickafus on Sunday October 9, 2016. The Class Notes belongs to MICRB 251 at Pennsylvania State University taught by Staff in Fall. Since its upload, it has received 4 views. For similar materials see /class/233065/micrb-251-pennsylvania-state-university in Microbiology at Pennsylvania State University.

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Date Created: 10/09/16
Microbiology 251 Notes from page 340-351 -small subunit -provides framework where tRNA are matched -large subunit -catalyze formation of peptide bonds to link amino acids -when not synthesizing protein, subunits are separate -A and P sites hold tRNA tightly if correct codon is added Elongation Factors EF-Tu -can simultaneously bond GTP and aminoacyl-tRNAs -initial codon to anticodon interaction occurs -small ribosomal subunit analyzes correctness of anticodon -if correct: -conformational change -this conformational change initiates GTP hydrolysis by EF-Tu -releases grip on aminoacyl-tRNA which it is also bound to -also (after EF-Tu dissociates), there is a time delay while amino acid moves into position on ribosome -time delay is longer for incorrect pairs -incorrectly matched tRNAs dissociate more rapidly -interaction with codon is weaker -tRNA will leave ribosome and won’t add amino acid -an incorrect codon-anticodon interactions in P-site causes increased misreading in A site -successive rounds of misincorporation lead to premature termination of protein by release factors -error is not corrected, flawed protein is subject to degradation instead kinetic proofreading -refers to the time delay that begins with an irreversible step -ie: ATP/GTP hydrolysis -an incorrect substrate is more likely to dissociate than a correct one -increases specificity at the cost of energy -tRNA in P-site contributes OH group which directly participates in catalysis of peptide bonds -ensures catalysis only occurs when tRNA is P-site is positioned correctly -ribozyme: -RNA molecules that possess catalytic activity -initiator tRNA-methionine complex (Met-tRNAi) -only initiator can bind to small ribosome subunit without complete ribosome -also directly binds to P-site instead of A-site -then, small subunit binds to mRNA molecule -recognized at 5’ end by its cap -small subunit searches for first AUG -ATP powered helicases help -in 90% of mRNAs, translation begins at first AUG encountered -initiation factors dissociate -allows large subunit to complete ribosome -nucleotides immediately surrounding start site influence efficiency of AUG recognition -selecting start codon in bacteria is different -no 5’ cap -each bacteria contains specific ribosome binding site (Shine-Dalgarno sequence) -located a few nucleotides upstream from AUG -forms base pair with small subunit polycistronic: -refers to bacterial mRNA -encode several different proteins translated from same mRNA molecule -eukaryotic mRNA usually encodes one protein of a set of closely related proteins stop codons: UAA, UAG, UGA -do not specify an amino acid -release factors bind to ribosome with stop codon in A-site -forces petidyl transferase in ribosome to add water molecule instead of amino acid to peptidyl tRNA -frees carboxyl end -as soon as enough mRNA has been translated for ribosome to out of the way, translation with another ribosome can begin -with same mRNA molecule -called a polyribosome/polysome -several ribosomes on mRNA molecule -about 80 nucleotides apart -bacterial mRNA can even begin translation before transcription is finished -bacterial mRNA doesn’t need a cap


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