We explain what viruses are and what types of viruses we can find. Also, how is its structure and some examples.
What is a virus?
A virus, in biology, is a microscopic and acellular parasitic agent, that is, it is much smaller than what is visible and is not composed of cells, but capable of reproducing only inside a host cell, taking advantage of the genetic replication mechanisms that it possesses and, in general, causing damage to the host cell. process.
Viruses can infect different forms of life: animals, plants, bacteria and even other viruses (so-called virophages), as they cannot survive on their own. There are them in almost all ecosystems In existence, they are the most abundant biological form on the planet: more than 5 thousand species are known since their existence was discovered in 1899, and it is believed that there could be millions of species.
The origin of these life forms is uncertain, as is the question of whether they are really alive, given how simple they are, little more than a genetic code looking for a cell to synthesize it. That seems to be his only job: injecting his DNA or RNA into a host cell and force it to synthesize new copies of the virus instead of the protein that she normally builds.
Some theories propose that viruses evolved from plasmids, that is, fragments of DNA of free life; while other theories prefer to think that they are bacteria or other cellular organisms that regressed, since the structure of any virus is much simpler than that of any cell.
In any case, they are very primitive organisms, with an enormous capacity for mutation that allows them to adapt and change constantly, and of which there is no fossil record: known virus species date back no more than 90 years.
Virus types
There are two ways of classifying viruses. The first includes four types, according to the structure they have:
- Helical. They have a helix shape and a central cavity where their genetic material (consisting of RNA or DNA) is found.
- Icosahedral. Medium spherical and symmetrical viruses. They are the most abundant of those that infect animals.
- Of wrapping. Viruses that possess a layer or envelope of lipids, which they obtain from the cellular membrane of its host cells, and which is used to inject genetic material into the cell.
- Complex There are viruses with more complex forms that combine the previous types and may even have additional components, such as protein tails to move around. They, in many cases, serve to inject the genetic material of the virus into the cell.
The second form of classification is based on the type of genetic material they contain:
- DNA virus. Those who have within them a molecule deoxyribonucleic acid, either single or double stranded. They need to introduce said DNA to the nucleus of the cell in order to start its replication.
- RNA virus. Those that have ribonucleic acid and can replicate directly in the cytoplasm cell phone, without the need to reach the core of the invaded cell.
Structure of a virus
Viruses are usually 100 times smaller than bacteria.
Most viruses are so tiny that they cannot be seen through microscopes opticians, except for some cases of large species (called girus). They are usually 100 times smaller than a bacterium and have very simple bodies, little more than protein frameworks that cover the viral genetic material.
In some cases, the outer part of their bodies has specialized proteins in disguise, which allow them to change their chemical appearance and not be recognized by the cells of the immune system. That is why viral diseases are recurrent and have no further treatment, except for certain retroviral drugs, such as those used to fight AIDS.
Examples of viruses
Some examples of known viruses are:
- Type 72 human enterovirus. This is the name that causes hepatitis A, one of the less dangerous and curable forms of the disease.
- Human papilloma virus. It is a family of extremely common viruses in men, some sexually transmitted (HPV) and others by touch, which usually cause warts and are mildly harmless, except for certain strains that have been linked to cancer.
- Herpes simplex virus (HSV). An extremely common human virus that generates skin lesions (known as herpes) and of which there are two variants: one genital and another that prefers the tongue, mouth, eyes and pharynx.
- Tobacco mosaic virus. It is an RNA virus that attacks plants (it was discovered in the tobacco plant) and produces whitish or yellowish spots on its leaves. It was the first virus discovered.