DNA Overview - Contrary to a common misconception, the DNA is not a single molecule, but rather a pair of molecules joined by hydrogen bonds: it is organized as two complementary strands, head-to-toe, with the hydrogen bonds between them. Each strand of DNA is a chain of chemical "building blocks", called nucleotides, of which there are four types: adenine (abbreviated A), cytosine (C), guanine (G) and thymine (T). Between the two strands, each base can only "pair up" with one single predetermined other base: A+T, T+A, C+G and G+C are the only possible combinations; that is, an "A" on one strand of double-stranded DNA will "mate" properly only with a "T" on the other, complementary strand; therefore, naming the bases on the conventionally chosen side of the strand is enough to describe the entire double-strand sequence. Two nucleotides paired together are called a base pair.

Transcription of DNA to RNA to protein: This "Central Dogma" forms the backbone of molecular biology and is represented by three major stages.

1. The DNA replicates its information in a process that involves many enzymes: replication.
2. The DNA codes for the production of messenger RNA (mRNA) during transcription.
3. Messenger RNA carries coded information to ribosomes. The ribosomes "read" this information and use it for protein synthesis. This process is called translation.

Proteins do not code for the production of protein, RNA or DNA. They are involved in almost all biological activities, structural or enzymatic.