Does anyone know? Are they life? Do they have DNA? Where did they come from? Expected answer No, No, They attach to DNA. No one knows.
Atta boy give it to him, No thing to do with you dear sir. Virus is inactive until they come in into a cell.
Does anyone know? Yes. Are they life? Strictly, no. They're snippets of DNA; but we don't consider them life because they can't reproduce without commandeering the machines of a living cell. Do they have DNA? Yes. DNA, wrapped in a casing. Where did they come from? They're snippets of DNA. They're part of the ecology of life at a genetic level. They move from life form to life form. But they came from existing life.
They are strands of DNA (or sometimes RNA) surrounded in the great majority of cases by protein shells of varying complexity. They have no cellular metabolism of their own and reproduce by entering into cells and by making use of the cell's machinery (such as protein synthesizing ribosomes and in many cases the necessary enzymes). A widely used way to classify viruses is called the 'Baltimore classification', named for biologist David Baltimore who thought it up. It classifies viruses into seven types, depending on whether they have DNA or RNA, whether it's single or double stranded and other details of the molecular biology of how they reproduce inside cells. (There's lots of variation and it can get very elaborate.) https://en.wikipedia.org/wiki/Baltimore_classification Viruses also differ a lot in their protein coats. Some are just featureless spheres, but others have lots of parts. (The virus' shell is important, since viruses have to make their ways through cell membranes. So the proteins on their coats will often bind with receptor sites on cells, stimulating them to engulf and ingest the virus. Others inject their DNA like hypodermic syringes. https://en.wikipedia.org/wiki/Bacteriophage The usual answer is 'no'. That's because they don't have any metabolism and they can't reproduce by themselves. They manage reproduction by hijacking living cells. Either DNA or RNA. Nobody knows. Considering that they need cells to reproduce, the most widespread idea is that they arose after cells did. But their (relative) simplicity does make the idea attractive that they are descended from the kind of pre-living chemical replicators that hypothetically also produced the first cells like LUCA (last universal common ancestor). Except that viruses would have subsequently lost the ability to reproduce on their own, perhaps because it was more efficient for them to use the cellular machinery of the cells around them. https://en.wikipedia.org/wiki/Viral_evolution
That's a great description. Thanks. Is there a name for this seemingly unintentional behavior that they exhibit - finding a suitable host, and doing things to it? I've seen a single celled organism chase down food and eat it. I would think it an electro-chemical interaction, but even that seems too complex for these little things. Like, where does that come from? I know, it's just the way they're made. Amazing stuff.
Answering what a virus is, is debatable. When my Biology class was covering the Three Domains of Life I asked my professor which category did they fall in; I already ruled out bacteria and they did not fall in eukarya and she said virus' are not in the archae category. She said virus' are their own beasts. I would think they would be in a class all their own?
The reason we don't classify viruses in a conventional format such as the one used for cellular organisms, is because we classify them specifically by their phenotypic characteristics, nucleic acid-types, morphology, modes of replication, and the specific ailments that they cause. Viruses are universally very different from one another, in such a way that categorizing them the same way doesn't make much sense.
