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, meaning they can remove nucleotides from the 5' end or the 3' end of the strand. In cellular processes, exonucleases are essential for maintaining the integrity of genetic material. They help eliminate damaged or unnecessary RNA and DNA, ensuring that only the correct sequences are preserved. This activity is vital for processes such as DNA replication, RNA processing, and genetic recombination.