There is no such thing as a simple form of DNA. Scientists know that by extracting the DNA from single celled organisms.
Virus Structure
Lecture 2: Virus Structure
All viruses contain the following two components: 1) a
nucleic acid genome and 2) a
protein capsid that covers the genome. Together this is called the
nucleocapsid. In addition, many animal viruses contain a 3)
lipid envelope. The entire intact virus is called the
virion. The structure and composition of these components can vary widely.
A: Viral Genomes: While the genomes of all known cells are comprised of double stranded DNA, the genomes of viruses can be comprised of single or double stranded DNA or RNA. They can vary greatly in size, from approximately 5-10 kb (
Papovaviridae, Parvoviridae, etc.) to greater than 100-200 kb (
Herpesviridae, Poxviridae). The known structures of viral genomes are summarized below.
DNA: Double Stranded - linear or circular
Single Stranded - linear or circular
Other Structures - gapped circles
RNA: Double Stranded - linear
Single Stranded - linear : These single stranded genomes can be either + sense, - sense, or ambisense The sense strand is the one that can serve directly as mRNA and code for protein, so for these viruses, the viral RNA is infectious. The viral mRNA from - strand viruses is not infectious, since it needs to be copied into the + strand before it can be translated. In an ambisense virus, part of the genome is the sense strand, and part is the antisense.
The genome of some RNA viruses is segmented, meaning that a virus particle contains several different molecules of RNA, like different chromosomes.