DNA Contains Genetic Information that is Inherited by Descendants

DNA is not a single molecule, but a pair of molecules that are interconnected by hydrogen bonds and organized so that their strands are complementary and antiparallel, from start to finish. Each strand of DNA consists of building blocks called nucleotides of which there are 4 types in DNA: adenine (A), cytosine (C), guanine (G) and thymine (T). These basic nucleic acid components can be polymerized in any order. Between the two chains, each base of one can be paired with the complementary base of the other chain so that adenine with two hydrogen bonds always joins with thymine and vice versa and cytosine always with guanine via three hydrogen bonds and vice versa. Thus we get possible combinations: A + T, T + A, C + G, G + C. In rare situations, mismatch occurs, eg when thymine converts to its enol form and cytosine to its imino form. The double- stranded structure of DNA provides a simple mechanism for DNA replication: DNA strands separate like zippers and thus open to a number of nucleotides in the environment. Enzymes create a new strand by looking for a complementary base in the environment and build a new strand of DNA. Of course, the base on the old chain determines which base will be on the new chain to preserve complementarity. Thus the cell completes replication with two copies of its DNA