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28 Cards in this Set
- Front
- Back
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Subunits of Prokaryotic Ribosomes
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50S+30S=70S
-50=23S rRNA, 5SrRNA, 34r Proteins -30=16SrRNA, 21 rProteins |
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Eukaryotic Ribosome Subunits
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60S+40S=80S
60=28S rRNA, 5.8 SrRNA, 5S rRNA, 50 r-Proteins 40=18S rRNA, 33 r-Proteins |
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Stages of Translation
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Initiation, Elongation, Termination
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In Prokary translation when/where does translation take place?
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simultaneously with transcription
in the cytoplasm |
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Prokaryotic Initiation-30S subunit serves as ____ to what?
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Serves as platform to assemble the Initiation Factors (IF)-IF1 and IF3
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Describe the "f" in fMet-what is it good for?
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Formic acid put onto the amino group to protect polypeptide vs reacivity. Only happens in bacteria so great target for antibiotics.
"Formics MET Ender"=Formic Acid=target for anitbiotics (Ender/meet their "END") |
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IF2 is what kind of protein/what does it bind to?
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G protein that carries GTP and binds to IF1, IF3 complex
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Steps of Prokary Initiation
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1) Binding of IF1/IF3 to 30S
2) Binding of IF2-GTP, fMet-tRNA, 30S with IF1 and IF3, mRNA 3)When binds to mRNA, IF1+IF3 released 4) 50S subunit binds 5) Hydrolysis of GTP after correct codon/anticodon pairing 6) Correct pairing releases IF2-GDP |
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What is the Shine-Dalgarno Sequence? Purpose?
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(prokary) sequence located just upstream of the AUG start codon.
-tells ribosome which AUG is the true start codon (prokary mRNA is polycistronic) |
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Eukaryotic Translation initation factors:
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eIF-1,-2,-3 (The 3 Elves like to initiate mischief)
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Ternary Complex=?
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eIF2-GTP-Met-tRNA
eIF2 is G Protein |
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Preinitiation Complex? what does it bind to? where does it bind? (eukary)
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Ternary Complex=eIF1,1A,3, and 40S subunit
binds to the mRNA via 5'cap |
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How is the actual preinitiation complex attached to the mRNA? (Eukary)
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preinitation complex binds to 5' cap of mRNA. connects with 4E cap-4G-eIF3-40S subunit-mRNA,
"4" units fire pre-initiation complex down the mRNA |
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Kozak sequence?
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AG-3, G+4, helps to recognize start codon via linear scanning of pre-initiation complex along the 5 UTR region
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Recognition of AUG in Eukary is found via...?
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found via linear scanning of mRNA by pre-initiation complex. Once complex finds AUG and proper base pairing occurs, ejects eIF2/GDP and binds the 60S subunits
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Elongation in Prokaryotes and Eukaryotes. Name the 3 elongation sites
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is practically the same
A, P, and E sites |
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What catalyzes the peptide bond in translation?
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Peptidyl Transferase
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Describe the process and steps of elongation
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-fMet-tRNA in P site
-next AA brought to A site by (EF-Tu-GTP-AA-tRNA) -Hydrolysis of GTP (dependent on correct base pairing in A site=proofreading mechanism) -Peptide bond forms, AA shifted to A site -EF-G stimulates GTP hydrolysis and whole thing moves from A to P site to start again. This shift causes ejection of old tRNA out of E site |
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Proofreading mechanism during elongation
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hydrolysis of GTP is dependent on the correct base pairings in the A site
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Characteristics of Polypeptide Chain Elongation
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1) Reading of mRNA template: coding sequence read in 5'-3' direction
2)Direction of Synth: Polypep grown from Amino end to carboxy end (A--C) 3) Polysomes multiple ribosomes translating a single mRNA molecule to improve efficiency 4) Translation efficiency= #ribosomes/mRNA molec. |
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Prokaryotic Elongation Factors
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EF-Tu, EF-Ts, EF-G
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Eukaryotic Elongation Factors
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eEF-1alpha, -1By, EF-2
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EF-Tu/eEF1alpha do what?
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recruit AA-tRNA to A site via hydrolysis of GTP (upon correct binding)
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EF-Ts/eEF-1By. what do they do?
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exchange the GDP-Pi for GTP to be used to active EF-Tu/eEF-1alpha
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EF-G/eEF2 do what?
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translocate the peptidyl tRNA from the A site to the P site via GTP hydrolysis
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Protein Chaperones do what?
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faciliate proper protein folding by binding/stabilizing unfolded or partially folded proteins
-enables protein to fold into proper conformation -prevent incorrect protein folding and/or protein aggregation -correct 3-D conformation of protein is determined by primary AA sequence examples: BiP and HsP |
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Termination steps
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1) Stop codon moves into the A site (no tRNA for stop codon)
2) Recognition of stop codon by Release Factors 3) Binding of RFs to the A site stimulates hydroylsis of bond btw the C terminal AA of polypeptide chaine and tRNA in P Site |
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Antibiotics that target translation
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steptomycin, target 30S, inhibits formation of 70S initition
tetracycline, target 30 S, inhibits binding of tRNAs to A site chloamphenicol, 50S subunit, inhibits peptidyl transferase rxn erythromycin, target 50S subunit, inhibits translocation from A to P site |
