Genetics Basic Concepts
When a cell reproduces, either through mitosis or meiosis, it must duplicate its DNA. This is called DNA replication. This step takes place just before cellular division.
DNA is shaped like a twisted ladder. Before replication can occur, the ladder needs to unwind and separate the two strands, essentially “unzipping” them. When DNA is “zipped,” the rungs of the ladder are held together by nitrogenous bases positioned opposite of one another. When the unzipping occurs, the nitrogenous bases break down. Special proteins (enzymes) then take over the job of recombining each half of the ladder by attaching new nitrogenous bases to their regular partners. There are four nitrogenous bases: adenine (A), thymine (T), cytosine (C) and guanine (G). A always pairs with T and C always pairs with G. The process continues along the full length of the zipper until two distinct and identical DNA molecules are produced.