Viruses are on the cusp of life and non-life. On one hand they have genetic material and use it to make more of themselves and evolve, on the other hand they don’t do anything outside of a host cell, they don’t breathe, grow, or move. If we count them as living, they are the most primitive form of life on Earth, but they certainly evolved after other forms of life because their existence depends on other cells. Viruses are custom designed to invade archaea, bacteria, animals and everything in between. In humans they are responsible for the common cold, chicken pox, influenza, polio and a host of sexually transmitted diseases like genital warts, HIV, herpes, and plenty others.
They are made of genetic material (single stranded or double stranded DNA or RNA) wrapped up in proteins. On their own, a virus can’t replicate themselves, they don’t have the machinery, the energy, or the building blocks. They get around this by sneaking into a cell and holding it at ransom, forcing it to make more and more viruses until they break the cell apart or sneak out one by one to infect other cells. Instead of a lust for gold, viruses have a lust for machinery and energy. They will board, hijack, rape, ravage and destroy to get what they want.
Cells aren’t fond of viruses, after all they screw up the well-organised operations that a good cell is proud of, so if a virus was to knock on the membrane and say “Hey, I’m a virus, can I come in please” the cell would likely sound an alarm for the immune system to come and kick some viral ass. Good thing for viruses (and not us) they are crafty indeed, and will decorate themselves with proteins that say “Hi, I’m full of food, come and eat me” or “Hi, I bear an important message from the brain. Let me in and I’ll tell you all about it” or they say nothing, just dock onto the outside of the cell and inject their genetic material. After all, it’s the genes that are important, the external proteins are just the boat.
Bacteriophages are viruses that infects bacteria, and there are buttloads of them, around 900 million bacteriophage in a milliliter at the surface of the sea, where bacteria are busy exhaling oxygen as they sun themselves. T4 (which infects e-coli) does it through the last method, and does it very effectively. They also look like a spider from Mars.
I’m gonna eat you. Yee!
Those legs attach to the outside of the bacteria, then it screws down and breaks through the membrane where it pumps out the genetic matter located in the head. Once inside the virus may either go lytic – launch a full attack, take over cellular process and devote all energy to making more viruses until SPLOOF! the cell ruptures and releases all the babies to start the process again, or go lysogenic – the viral DNA will slip into the bacterial chromosome and act like it belongs, hiding in plain sight and being carried through the generations until it launches a mutiny and starts the lytic cycle again. Some viruses just go for the lytic cycle all the way, and they be the truest pirates of the cell (the others being ninja pirates.)
So next time ye are coughing and sickly with a viral infection, be glad ye are not e-coli with a big spider thing attached to you, and spare a thought for the pirates of the cell. Though they may not be strictly alive, they are just making a living and don’t mean to make you ill, after all a dead host is no use to them. We wage war against the pirates near every day, getting sick is nothing more than collateral damage.