تسجيل الدخول

تسجيل

DNA Replication:- DNA Is Degraded by Nucleases

المؤلف:  David L. Nelson، Michael M. Cox

المصدر:  Lehninger Principles of Biochemistry

الجزء والصفحة:  952

2026-07-19

47

DNA Replication:- DNA Is Degraded by Nucleases

To explain the enzymology of DNA replication, we first introduce the enzymes that degrade DNA rather than synthesize it. These enzymes are known as nucleases, or DNases if they are specific for DNA rather than RNA. Every cell contains several different nucleases, belonging to two broad classes: exonucleases and endonucleases. Exonucleases degrade nucleic acids from one end of the molecule. Many operate in only the 5→3 or the 3→5 direction, removing nucleotides only from the 5 or the 3 end, respectively, of one strand of a double stranded nucleic acid or of a single-stranded DNA. Endonucleases can begin to degrade at specific internal sites in a nucleic acid strand or molecule, reducing it to smaller and smaller fragments. A few exonucleases and endonucleases degrade only single-stranded DNA. There are a few important classes of endonucleases that cleave only at specific nucleotide sequences. You will en counter many types of nucleases in this and subsequent chapters.