Semiconservative replication refers to

If a bacterial molecule uses SO₄²⁻ (sulfate) as its final electron acceptor, the process is anaerobic, not aerobic. Aerobic respiration specifically requires oxygen (O₂) as the terminal electron acceptor in the electron transport chain. In contrast, certain bacteria can perform anaerobic respiration, using alternative electron acceptors such as sulfate, nitrate, or carbon dioxide. In sulfate-reducing bacteria, sulfate is reduced to hydrogen sulfide (H₂S) during energy production, allowing ATP synthesis in the absence of oxygen. Therefore, using sulfate as the terminal electron acceptor defines an anaerobic metabolic pathway.

A. Deletion: A deletion mutation removes one or more nucleotides from the DNA sequence. While deletions can lead to frameshifts and potentially premature stop codons, the key feature in this scenario is the introduction of a stop signal, not the removal of nucleotides per se.

B. Nonsense: A nonsense mutation changes a codon that encodes an amino acid into a stop codon. In this example, “THE CAT ATE THE BIG RAT” is truncated to “THE CAT ATE (stop),” indicating translation terminates prematurely. This type of mutation produces a truncated, usually nonfunctional protein.

C. Silent: A silent mutation changes a nucleotide without altering the amino acid sequence. It does not produce a stop codon or truncate the protein, so it would not result in “THE CAT ATE (stop).”

D. Missense: A missense mutation changes a codon so that a different amino acid is incorporated. While it alters the protein sequence, it does not introduce a stop codon, so it cannot account for the premature termination seen here.

E. Insertion: An insertion adds one or more nucleotides into the sequence. Like deletions, insertions can cause frameshifts that might eventually produce a stop codon, but the defining characteristic in this example is the direct conversion of a codon to a stop codon, making this a nonsense mutation rather than a generic insertion.