Final answer:
Endonucleases cleave DNA internally at specific sequences, useful for creating DNA fingerprints and molecular cloning, while exonucleases remove nucleotides from the ends of DNA, such as in DNA replication and repair.
Step-by-step explanation:
An endonuclease is an enzyme that cleaves DNA internally at specific sequences with a high degree of specificity. This characteristic allows restriction endonucleases to provide a "DNA fingerprint" by creating a unique pattern of DNA fragments after cleavage. For instance, the recognition and cutting at specific unmethylated DNA sequences distinguishes foreign DNA from host DNA, enabling the selective cleavage of the former.
Conversely, an exonuclease cleaves DNA from the ends, either removing nucleotides one at a time or in chunks. An example of exonuclease activity is the removal of RNA primers during DNA replication by DNA polymerase I, which has a domain with 5'→3' exonuclease activity.
Restriction enzymes use a metal-activated water molecule to enhance their cleavage efficiency, acting as a strong nucleophile able to break the phosphodiester bond in the DNA backbone. These enzymes play a crucial role in DNA repair, recombination, and in biotechnological applications such as molecular cloning.