DNA can be found inside the nucleus of every cell, apart from red blood cells. It's tightly wound and spread throughout the 46 chromosomes. One set of 23 chromosomes is inherited from each parent. Inside the chromosomes the DNA exists as genes. A gene is a sequence of DNA, that by and large, though there are exceptions, codes for one protein. There is large volume of so-called 'junk DNA' that apparently serves no purpose, although there are bodies of work that are starting to show otherwise.
These are tiny organelles that are the energy factories of the cell. They contain a small amount of DNA that is distinct from nuclear DNA. For the most part mitochondrial DNA is inherited from the mother in sexually reproducing species.
Plants and Animals
In plants and animals DNA is also found in the cell nucleus. The DNA of all animals is very similar. The major differences are in the number of chromosomes and genes, and the arrangement of base pairs within these genes.
A virus is essentially a very simple particle with nucleic acid at its core and a few essential proteins, such as its protein coat. The nucleic acid can be either DNA or RNA, depending on the kind of virus it is. The DNA can also be either single stranded or double stranded. Examples of viruses with a double stranded DNA molecule are; Herpes simplex virus and the small pox virus. Examples of viruses with a single stranded DNA molecule are; Adeno-associated virus and the M13 bacteriophage – it infects bacteria. Viruses do not possess nuclei.
The DNA is not enclosed inside a nucleus. It's free-floating as it is inside a virus. It's usually a single coil of DNA. In some bacteria there's additional DNA and this is located in structures known as plasmids. The DNA here is not essential to the survival of the bacterium.
DNA in Space
Well …. every time an astronauts blasts off. Digitized versions of personal DNA sequences will soon be sent up as part of a publicity drive to promote the Archon X $10 million genome sequencing prize. Among those whose DNA will be digitized are physicist and best-selling author Prof Stephen Hawking and the comedian Stephen Colbert.