A complementary DNA strand refers to a specific pairing between the nucleotides of one strand of DNA with another. In the DNA double helix, each strand is made up of a sequence of nucleotides, which consist of a sugar, a phosphate group, and a nitrogenous base. The four types of nitrogenous bases in DNA are adenine (A), thymine (T), cytosine (C), and guanine (G).
The key aspect of complementary strands is the base pairing rules: adenine pairs with thymine, and cytosine pairs with guanine. This means that if one strand has the sequence ACGT, the other strand will have the complementary sequence TGCA. This pairing is crucial for the replication of DNA and for the proper functioning of cells.
Complementarity allows for accurate copying of genetic information during cell division because each strand serves as a template for creating a new complementary strand. This process ensures that the genetic code is preserved and transmitted from one generation of cells to the next.