The properties and behaviour of viruses differ according to their nucleic acid content. Unlike cells (e.g. bacteria, plant and animal cells), viruses contain either DNA or RNA, never both; the viral nucleic acid is either single or double stranded.
Viruses typically store their genetic information encoded in molecules of either DNA or RNA -- either one or the other but not both. In April of 2012, however, scientists at Portland State University discovered an unusual virus with a genome made from both RNA and DNA.
Unlike DNA viruses which must always transcribe viral DNA into RNA to synthesize proteins, RNA can skip the transcription process. Furthermore, some RNA molecules can act as mRNA being translated directly into protein.
They're also called retroviruses because they operate "backwards" from the way cells and DNA viruses do. Cells and DNA viruses have DNA, which they use to make RNA. RNA viruses have RNA and use it to make DNA.
Most bacteria have a genome that consists of a single DNA molecule (i.e., one chromosome) that is several million base pairs in size and is "circular" (doesn't have ends like chromosomes of eukaryotic organisms).
River water, lake water, and seawater contain DNA belonging to organisms such as animals and plants. Ecologists have begun to actively analyze such DNA molecules, called environmental DNA, to assess the distribution of macro-organisms. Challenges yet remain, however, in quantitative applications of environmental DNA.
Viruses did not evolve first, they found. Instead, viruses and bacteria both descended from an ancient cellular life form. But while – like humans – bacteria evolved to become more complex, viruses became simpler.
In fact, the actual structure of the DNA molecule and how it codes for proteins is the same from bacteria to yeast to plants and animals. The DNA molecules in plants, humans, and all living things are all the same shape -- like a twisted ladder, or a double helix.
Definition. A virus is an infectious microbe consisting of a segment of nucleic acid (either DNA or RNA) surrounded by a protein coat. A virus cannot replicate alone; instead, it must infect cells and use components of the host cell to make copies of itself.
DNA viruses contain DNA in the genome while RNA viruses contain RNA. The replication of DNA viruses occurs inside the host's nucleus while it occurs in the host's cytoplasm in RNA viruses. The main difference between DNA and RNA viruses is the type of genetic material and replication inside the nucleus.
The first human virus to be identified was the yellow fever virus. In 1881, Carlos Finlay (1833–1915), a Cuban physician, first conducted and published research that indicated that mosquitoes were carrying the cause of yellow fever, a theory proved in 1900 by commission headed by Walter Reed (1851–1902).
Abstract. Two scientists contributed to the discovery of the first virus, Tobacco mosaic virus. Ivanoski reported in 1892 that extracts from infected leaves were still infectious after filtration through a Chamberland filter-candle.