An organism's genes are contained in its DNA (or in its RNA for many types of viruses, which, technically, are not organisms, at least not in any sense with respect to their dormant state). An organism's genome is the entirety of its hereditary information, consisting of both the genetic and the structural sequences of its combined DNA. The Oxford English Dictionary suggests the name to be a blend of the words gene and chromosome. The genome is the master blueprint of an organism's essential design and dynamics.
The main difference between DNA and RNA is the sugar present in the molecules. While the sugar present in an RNA molecule is ribose, the sugar present in a molecule of DNA is deoxyribose. Deoxyribose is the same as ribose, except that the former has one more OH (oxygen-hydrogen group).
DNA does not usually exist as a single molecule, but instead as a tightly-associated pair of molecules. These two long strands entwine like vines, in the shape of a double helix. This arrangement of DNA strands is called antiparallel. The asymmetric ends of DNA strands are referred to as the 5′ (five prime) and 3′ (three prime) ends. One of the major differences between DNA and RNA is the sugar, with 2-deoxyribose being replaced by the alternative pentose sugar ribose in RNA. The four bases found in DNA are adenine (abbreviated A), cytosine (C), guanine (G) and thymine (T). A fifth pyrimidine base, called uracil (U), usually takes the place of thymine in RNA and differs from thymine by lacking a methyl group on its ring.
