1In today's lecture, we will examine how cells copy their genetic material with astonishing accuracy before every division.
2Contrary to what many assume, replication is not a single enzyme working alone but a coordinated molecular machine.
3The double helix must first be unwound by helicase, an enzyme that breaks the bonds between paired bases.
4What I want to emphasize here is the remarkable proofreading ability of the enzyme DNA polymerase.
5When an incorrect base is inserted, the polymerase pauses, reverses, and removes the error before continuing.
6It is not speed but accuracy that defines this enzyme, although it manages to achieve both impressively well.
7Early models proposed the copying machinery moved continuously, though later work showed one strand is assembled in fragments.
8These fragments, named after the scientist who discovered them, are later joined together by another enzyme.
9The experiment was originally designed to measure error rates, but it unexpectedly revealed a second repair system.
10Let me give you a concrete example of why this matters: unrepaired errors can accumulate and eventually trigger disease.
11So, in summary, replication combines speed with multiple layers of checking, a balance evolution has refined over millennia.