Final answer:
Nonsense mutations introduce stop codons (UAA, UAG, UGA) into mRNA causing ribosome stalling and premature termination of protein synthesis. A release factor then promotes the release of the polypeptide and disassembly of the ribosome.
Step-by-step explanation:
Mutations tat cause a ribosome to stop translating the mRNA at the site of the mutation and prematurely terminate protein synthesis are known as nonsense mutations. These mutations change a codon that originally specified an amino acid into one of the three stop codons: UAA, UAG, or UGA. When a ribosome encounters a stop codon during the translation process, no corresponding tRNA can recognize these codons, leading to the stalling of the ribosome. This pause allows a protein release factor to enter the A site of the ribosome, promoting the release of the newly synthesized polypeptide and leading to the disassembly of the ribosomal subunits from the mRNA. This entire process is energy-dependent, consuming GTP in the form of hydrolysis. Should hthe 60S ribosomal subunit become nonfunctional due to mutation, translation would stall after the initiation AUG codon, as this subunit is essential for proper translation elongation and termination.