This animation shows the process of DNA replication, including details about how the mechanism differs between the leading and lagging strand.

DNA replication starts with the separation of the two DNA strands by the enzyme helicase. The two strands are referred to as the 3' and 5' strands based on the direction by which the component nucleotides are joined. The 3' DNA strand is also known as the leading strand; DNA polymerase copies the leading strand to produce a complementary strand. The 5' strand is also known as the lagging strand. DNA polymerase copies the lagging strand in sections. These two different mechanisms of copying DNA occur because DNA polymerase can only synthesize DNA in the 5' to 3' direction.

This animation brings the DNA replication process to life, showing three-dimensional representations of the molecules involved. Depending on students’ backgrounds, it may be helpful to pause the animation at various points to identify the molecules and describe their interactions.