Translation Occurs in Three Phases – Flashcards
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initiator tRNA
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tRNA carrying the first amino acid in the polypeptide
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translation initiation in eukaryotes and bacteria
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small ribosomal subunit binds near the 5 end of mRNA and identifies start codon sequence
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final stage of initiation
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large subunit joins small subunit to forma intact ribosome and translation begins
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final stage of initiation
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large subunit joins small subunit to forma intact ribosome and translation begins
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second stage of initiation
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initiator tRNA binds to start codon
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charged tRNA
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tRNAs used during translation that carry a specific amino acid
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uncharged tRNA
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tRNA without an amino acid
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initiator factor proteins
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help control ribosome formation and binding of the initiator tRNA
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E. coli molecular components for initiation
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1. mRNA 2. small ribosomal subunit 3. large ribosomal subunit 4 initiator tRNA 5. 3 essential initiation factor proteins 6. GTP
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initiation factor for translational initiation in bacteria
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IF3. affiliated with 30s ribosomal subunit. prevents the 30s subunit from binding to the 50s subunit. small subunit IF3 complex binds near the 5 end of mRNA, searching for AUG sequence that serves as start codon (Shine-Delgarno sequence)
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preinitiation complex
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forms when the authentic start codon is identified by base pairing that occurs between the 16srRNA in the 30s ribosome and a short mRNA sequence located a few nucleotides upstream of the start codon in the 5 UTR of mRNA
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Shine-Delgarno Sequence
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consensus sequence that is purine-rich located 3-6 nucleotides upstream of the start codon. complementary sequence found near 3 end of 16s rRNA and pairs with this sequence to to position mRNA on 30s subunit
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step 2 bacterial translation initiation
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initiator tRNA binds to start codon at what will be P site after ribosome assembly.
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amino acid on initiator tRNA
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modified methionine is called N-formylmethionine (fMet).
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end of step 2 bacterial translation initiation
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30s initiation complex, tRNA fMet located at start codon, 3 initiation factors, and a molecule of GTP formed
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final step of bacterial initiation
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50s subunit joins 30s subunit t oform intact ribosomes. IF1, 2, 3 disassociate and create 70s initation complex.
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preinitation complex eukaryotic translation
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eukaryotic 40s ribosomal subunit complexes with eukaryotic initiation factor proteins and with charged tRNAmet
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step 1 eukaryotic translation initiation
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preinitiation complex recruited to 5-cap reigion of mRNA
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step 2 eukaryotic translation initiation
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preinitiation complex joins eIF4 complex. this makes up the initiation complex
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eIF4 complex
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group of at least 4 eIF4 proteins that assembles at the 5 cap independently of translational initiation
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step 3 eukaryotic translation initiation
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scanning: uses ATP hydrolysis to move the small ribosomal subunit through the 5 UTR in search of start codon.
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Kozak sequence
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specific consensus sequence of eukaryotic mRNA that contains the authentic start codon (AUG) sequence
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step 4 eukaryotic translation initiation
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60s complex recruited to complex. 80s ribosome formed. dissociation of the eIF proteins.
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elongation factors facilitate three steps of polypeptide synthesis how:
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1. recruitment of charged tRNAs to A site 2. formation of peptide bond between sequential amino acids 3. translocation of ribosome in 3 direction
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step 1 bacterial/eukaryotic translation elongation
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tRNA recruitment: accompanied by elongation factor protein, charged tRNA enters A site
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step 2 bacterial/eukaryotic translation elongation
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Peptide bond formation: peptidyl transferase catalyzes formation of a peptide bond between the amino acids in the P and A sites. peptide chain moves to the A site
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step 3 bacterial/eukaryotic translation elongation
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Translocation: elongation factors translocate ribosome; uncharged tRNA released to the E site and a new tRNA is recruited to A site
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when does elongation cycle stop
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one of 3 stop codons enters A site of ribosome. no tRNAs with anticodons complementary to stop codons.
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Release factors
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used by bacteria and eukaryotics. bind to a stop codon in the A site. polypeptide bound to tRNA at P site released by hydrolysis of GTP, which is complexed with RF.
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bacteria release factors
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2 release factors (RF1 and RF2) recognize stop codons.
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eukaryotic release factors
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single release factor called eRF that recognizes all 3 stop codons
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three phases of translation
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initiation elongation termination
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three phases of translation
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initiation elongation termination
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three phases of translation
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initiation elongation termination
