Final answer:
Endonucleases are enzymes that cleave DNA internally at specific sites, and are not primarily involved in removing bases sequentially from the ends of DNA strands. Specific endonucleases, like AP endonuclease, are part of the DNA repair machinery, while restriction endonucleases serve in molecular biology applications such as DNA fingerprinting.
Step-by-step explanation:
An endonuclease is an enzyme that cleaves the phosphodiester bond within a polynucleotide chain. Contrary to the suggestion in the question that an endonuclease removes bases sequentially from one end of the DNA, endonucleases act at specific sites within the DNA. A special type of endonuclease involved in DNA repair is the AP endonuclease, which acts after a DNA glycosylase removes a damaged base. The AP endonuclease then makes a nick in the DNA backbone at the site of the base-less sugar, allowing for further action by enzymes such as phosphodiesterase and DNA polymerase to process and repair the DNA strand.
Restriction endonucleases are other examples of endonucleases, which cleave DNA at specific sequences to produce DNA fragments, with applications ranging from genetic fingerprinting to molecular cloning. These should not be confused with exonucleases, which remove nucleotides from the ends of DNA strands, often functioning in DNA replication and repair to remove RNA primers and replace them with DNA nucleotides.