Definition: DNA, which stands for deoxyribonucleic acid, is the information storage system of the body. Made of strands of linked nucleic acids, DNA spells out the recipes for all the components of a cell. These recipes are known as genes.
In humans and other complex organisms, DNA is found in the form of chromosomes in the nucleus of cells. Each chromosome is made up of paired, complementary strands of DNA that are twisted into a double helix (picture a twisted step ladder).
When a cell divides, one strand of each chromosome goes into each of the new cells created from the split. These cells can then generate new matching strands to complete the pairs on their own.
Although most organisms store their genetic codes as DNA, a small number of viruses, known as retroviruses, use RNA as their information storage system instead. An RNA genome may give several advantages to a retrovirus, such as smaller sizes and faster mutation rates than are possible with DNA genomes.
Examples:
Hepatitis A is an RNA virus, but hepatitis B is a DNA virus.
