Antiparallel (biochemistry)

Illustration of the hydrogen bonding patterns, represented by dotted lines, in an antiparallel beta sheet. Oxygen atoms are colored red and nitrogen atoms colored blue.

In biochemistry, two molecules are antiparallel if they run side-by-side in opposite directions or when both strands are complimentary to each other.

In DNA, the 5' carbon is located at the top of the leading strand, and the 3' carbon is located at the lower section of the lagging strand. The nucleotides are similar and parallel, but they go in opposite directions, hence the antiparallel designation. The antiparallel structure of DNA is important in DNA replication because it unzips the leading strand one way and the lagging strand the other way. During DNA replication the leading strand is replicated continuously whereas the lagging strand is replicated in segments known as Okazaki fragments.