TimmahTao
Active Member
Okay, viruses are what are known as obligate parasites. In other words, their entire lifecycle is dependent on stealing resources/tools/energy from other forms of life. They can't reproduce on their own; billions of years of evolution favored the loss of that ability. Evolutionarily, the question of life answered by viruses is, "Why bother to make your own reproductive tools when you can steal the energy, tools (enzymes), and materials (amino acids/nucleotides) from someone else who will do all the work for you?"
To make an analogy (loosely), you can think of viruses as hijackers or, more accurately, agents of industrial espionage. They work their way into a production facility (the cell) and, in a variety of ways, trick the factory into making the tools they need to hijack other factories in the same way.
Some viruses just feed their code into the machines and manufacturing tools (ribosomes) directly, which start spitting out the components of more viruses (viral genome/proteins/etc) instead of what they were supposed to produce (normal cellular proteins and enzymes.) This is how coronaviruses work. The cellular machinery will only make more viruses if the directions to do so are present. The directions, in the form of RNA are transient and prone to damage, so they only last as long as the virus is physically present, or not much longer.
Other hijackers (viruses) are less direct. Instead of hijacking the machinery directly, they insert their code into the bank of blueprints and instructions stored in the facility that controls production throughout the entire cellular factory (DNA in the nucleus.) By adding their DNA (directly or indirectly) to the genetic code in the nucleus, they ensure that whenever the cellular machinery activates that portion of DNA, the viral DNA will get copied, transcribed to RNA, and translated into proteins by the ribosomes. Even if the virus isn't present in a persons' body, the DNA it added to the genome IS, and will be for the entire lifetime of that cell and all its descendants. In fact, anywhere from 5-8% of the total DNA in your body is the defective/nonfunctional remains of viral hijackings (by retroviruses, specifically) in your evolutionary history. These infections can be chronic, recurring, or dormant for decades and then get 'reactivated' when something (like stress, or other disease) triggers the activation of that DNA. Retroviruses and DNA viruses work this way; think HIV and Herpes viruses (of all sorts, including chicken pox).
