AP BIOLOGY

Detailed explanation-1: -Proteins known as release factors bind to any ribosome with a stop codon positioned in the A site, and this binding forces the peptidyl transferase in the ribosome to catalyze the addition of a water molecule instead of an amino acid to the peptidyl-tRNA (Figure 6-73).

Detailed explanation-2: -A stop codon tells the ribosome and transfer DNA that the process can stop and the new polypeptide chain can be released. If ribosomes and transfer DNA are still a mystery, either read on or visit the protein synthesis page. Without stop codons, an organism is unable to produce specific proteins.

Detailed explanation-3: -The tRNA that has given up its amino acid is released. It can then bind to another molecule of the amino acid and be used again later in the protein-making process.

Detailed explanation-4: -When the mRNA stop codon is reached, the fully synthesized protein does not simply fall off the ribosome. Release factors (RFs) are the protein assistants that recognize the presence of a stop codon in the ribosomal A-site and trigger cleavage of the polypeptide from the P-site tRNA (Fig. 9).

Detailed explanation-5: -Most codons in messenger RNA correspond to the addition of an amino acid to a growing polypeptide chain, which may ultimately become a protein; stop codons signal the termination of this process by binding release factors, which cause the ribosomal subunits to disassociate, releasing the amino acid chain.