What is a key characteristic of exonucleases compared to endonucleases?

Exonucleases are enzymes that play a crucial role in nucleic acid metabolism by digesting nucleic acids from the ends of the molecule. This characteristic distinguishes them from endonucleases, which cleave nucleic acids at specific sites within the molecule itself, not just at the terminal ends.

The ability of exonucleases to remove nucleotide residues one at a time from either the 5' or 3' ends allows for precise trimming and processing of nucleic acids, which is essential in processes such as DNA replication and repair, as well as RNA degradation. This end-dependent activity underscores their importance in maintaining the integrity and functionality of nucleic acids within the cell.

In contrast, the other options do not accurately describe the unique action of exonucleases. They do not function primarily on specific sequences or only in RNA molecules. In fact, both exonucleases and endonucleases can act on various types of nucleic acids, including DNA and RNA, making the correct identification of their mechanisms essential for understanding molecular biology processes.