Viruses

A virus is essentially a small genome floating around in a protein-made shell called a "capsid", and some special viruses have an envelope made of organic compounds called lipids. The word "virus" comes from latin for "poison". They come in three different general shapes, those being icosahedral (D20 shaped), filamentous (thread-like), or head-tail (a combination of the two previous ones). They, like other microorganisms, have an extremely short lifespan, only a few hours or a few days, also meaning that they reproduce extremely quickly. Because of this, they evolve extremely quickly, so they can easily evolve drug resistance, which is a reason that there is a new influenza vaccine every year. Viruses are extremely abundant in the natural world, and almost every living organism hosts at least a virus! In fact, there is an estimated ten billion billion trillion (10^31) viruses on Earth that could stack up to a hundred million lightyears. For context, that is almost five hundred Milky Way galaxies lined up! In organisms, viruses invade the cells, using them to reproduce. This happens through a complex cycle that would take too long to completely explain here, so we will keep it short. Viruses reproduce in a cycle. This is the lytic cycle, which is the most common and straightforward one, and it has five stages. The first stage is simply when the virus attaches onto a cell. The second stage is entry, where the virus injects its genome into the host cell. This could happen inside the cytoplasm or the nucleus, and the genome could be in either DNA or RNA, depending on the type of virus and the host, but we won't go too into detail here. Essentially, now, the cell is coded to produce the proteins of the virus. Next, the DNA gets replicated inside the host cell. In this stage, the proteins necessary to make the capsids are created, but still lie around doing nothing. This is where the next stage comes in. In this stage, the proteins are assembled into new viruses. Finally, the virus pokes holes through the cell membrane or cell wall for plants. This will cause the host cell to explode like a microscopic water ballon. After that, the viruses swarm out, looking for more unfortunate cells to be their host, and the cell bursting is called "lysis" hence the name "lytic". Without the cell host, viruses cannot reproduce, so there are multiple arguments for whether viruses are living or not. Another way that they differ from all the other organisms is how their genome is very small. They only have a few thousand to a few hundred thousand nucleotides. Nucleotides are the fundamental "building" block molecules found in DNA and RNA. On the other hand, the bacterium that causes strep throat has seven million nucleotides in their genome, human have six billion, and a certain record-holding species of fern has 160 billion nucleotides in its genome. Additionally, most viruses are only a fiftieth of a bacterium's length, though these sections of organisms contain millions of species who have millions of members, and mega-viruses exist. Because of how unique they are, viruses have their own taxonomy, apart from plants, animals, and all other single-cell organisms.

More viruses coming soon!