Exonucleases are enzymes that play a crucial role in the process of DNA and RNA metabolism. They work by removing nucleotide units from the ends of a nucleic acid chain, which can help in DNA repair, replication, and degradation. These enzymes can be specific to either DNA or RNA and can function in both directions, either from the 5' end or the 3' end of the nucleic acid strand. In cellular processes, exonucleases are essential for maintaining the integrity of genetic material. They help eliminate damaged or unnecessary nucleotides, ensuring that the genetic information remains accurate. Their activity is vital for processes such as DNA replication, RNA processing, and cellular response to damage.