Thymidine analogs are synthetic compounds that resemble the natural nucleoside thymidine, which is a building block of DNA. These analogs are often used in research and medicine to study DNA synthesis and repair, as well as to develop antiviral and anticancer therapies. By mimicking thymidine, they can interfere with the replication of viral DNA or the growth of cancer cells. In addition to their therapeutic applications, thymidine analogs can also be used as tools in molecular biology. They help scientists understand the mechanisms of DNA replication and repair processes. Some well-known thymidine analogs include azidothymidine (AZT), used in the treatment of HIV, and 5-bromodeoxyuridine (BrdU), commonly used in cell proliferation studies.