An elongating ribosome is bound to appropriate tRNAs in both the A and P sites and is ready for peptidyl transfer. What happens next? A. The carboxyl end of the polypeptide chain is released from the P-site tRNA and joined to the free amino group of the amino acid linked to the A-site tRNA. B. The carboxyl end of the amino acid is released from the A-site tRNA and joined to the free amino group of the polypeptide chain linked to the P-site tRNA. C. The tRNA with the growing peptide chain is translocated to the E-site where the amino acid from the A-site tRNA will be linked to the polypeptide chain. D. The tRNA with the amino acid attached is translocated to the E-site before it is linked to the growing polypeptide chain.
Added by Dana P.
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Step 1: The carboxyl end of the polypeptide chain is released from the P-site tRNA. Show more…
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A ribosome has a tRNA in its P site that is attached to a polypeptide. The ribosome's A site is sitting over a stop codon. What will happen next? The stop amino acid will be added to the polypeptide chain, and the polypeptide will be released. A terminator tRNA will bind in the A site of the ribosome, and the polypeptide will be released. A protein called a release factor will bind to the A site and the bond between the tRNA in the P site and the polypeptide chain will be hydrolyzed. The ribosome will shift three nucleotides toward the 3' end of the mRNA to expose the next codon in the A site
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The table below gives the ribosome's P and A sites in different states when it is engaged in protein synthesis. Ribosome P site | Ribosome A site A. filled with tRNA attached to growing polypeptide | filled with amino-acylated tRNA B. filled with amino-acylated tRNA | filled with tRNA attached to growing polypeptide C. empty | filled with amino-acylated tRNA D. filled with uncharged tRNA | filled with tRNA attached to growing polypeptide E. filled with tRNA attached to growing polypeptide | empty In the Table, which one gives the status of the P site and the A site at the instant just before the ribosome forms a peptide bond? A. row A of the table B. row B of the table C. row C of the table D. row D of the table E. row E of the table
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When the ribosome reaches a nonsense codon, which of the following occurs? a. a methionine is incorporated b. the polypeptide is released c. a peptide bond forms d. the A site binds to a charged tRNA
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