This animation shows how mistakes made during DNA replication are repaired by the cell.

Replication mistakes may occur as DNA polymerase copies the DNA strands. One type of mistake, called a mismatch, happens when the polymerase incorporates the wrong nucleotide into a strand. The animation illustrates how mismatches can be fixed with a set of repair proteins. These proteins recruit an enzyme called EXO1 to remove the incorrect section. DNA polymerase then replaces the removed section with the correct nucleotides.

This animation is a clip from a 2003 Holiday Lecture Series, Learning From Patients: The Science of Medicine. Depending on students’ background, it may be helpful to pause the animation at various points to discuss different structures or proteins.