When talking about living beings, no discussion is generated by indicating that an animal or a plant is one. It is the same with fungi, algae and bacteria. But when it comes to viruses, things change . And that is because these infectious agents break the rules.

Firstly, they are not cells, but simple protein structures, but they do contain genetic material. Second, their only way to reproduce is through infection of cells, to use their tools for this purpose. And third, they do not need to obtain any kind of energy, since they do not require maintenance.

Apart from the discussion of considering them living beings or not, there is variety both in their content and in their structures, which has made it possible to identify different types of viruses . The importance of knowing them better has to do with their role in causing diseases in living beings, some of which are more serious than others. A better knowledge helps to prevent and treat them.

Basic structure of a virus

Viruses stand out from anything else because they are so simple in composition. It is a protein structure, with greater or lesser complexity depending on the class, which aims to protect the genetic material it carries , while acting as a vehicle for it.

Capsule

The main structure that all viruses have is the capsid. Formed by a set of protein units called capsomers , when it stores the genetic content it changes to be called the nucleocapsid. The form that this piece takes is one of the criteria for identifying types of viruses.

The nucleocapsid can have an icosahedral symmetry , which is observed as a spherical shape; a helical symmetry, which is stick or tubular in shape; and of complex symmetry, apart from the nucleocapsid, it has attached to it a protein structure that is called as a whole as a tail, which acts as a support to facilitate the insertion of the content into a host.

Wrap

Independent of this, some viruses can have a second layer, which is called the envelope, which is configured by lipids. Their presence or absence is another criterion used to classify them.

Types of viruses according to their genetic material

Unlike cells, the genetic content of these infectious agents is most varied in classes and configurations, so this is a good point for use in taxonomy. Broadly speaking, there are two main types of virus : those that contain DNA as genetic material and those that store their information in the form of RNA.

DNA virus

DNA virus types possess a small chain of nucleic acids that can be either single or double-stranded, i.e. in one or two strands. Furthermore, it can be in a circular or linear form, all depending on which virus we are talking about. They are the most common viruses to be found. For example, the cause of herpes (Herpesviridae) has genetic content that is in the form of linear bi-stranded DNA.

RNA virus

As you can imagine, the only difference between RNA viruses and the others is in the nucleic acids. It is the same: it can be formed by one or two chains, and be in a linear or circular form. A well-known example is the family of retroviruses (Retroviridae), among the diseases that can cause AIDS. In this case, it presents its genetic material in the form of single-stranded linear RNA.

According to what they infect

Not all types of viruses have an affinity for the same organisms or cells. In other words, some viruses only affect animals and not plants . Because of this, it can be used as a criterion for classification. In this case it focuses on which is its host, there being three groups:

  • Animal viruses.
  • Vegetable viruses.
  • Bacteriophage virus (attacks bacteria).

How do they work?

I could not finish this article without explaining how viruses work in a generic way. The virus (mature form of the virus), locates a host cell, managing to introduce its genetic content inside it. This material is inserted into the DNA of the nucleus, so the cell can transcribe its information and translate it into the proteins that make up the capsid and so on. It is also possible to replicate the genes of the virus, in order to introduce it into the new capsides and form new virons that leave the infected cell.

This is a generic way of talking about the life cycle of viruses; there are many variables. Examples cited as retroviruses, first have to transcribe their RNA content into DNA and manufacture the complementary chain before they can be inserted, since cells contain their genetic material in the form of two-stranded DNA.

The cause of viruses generating disease is due to this insertion into the cell’s DNA, which can translocate genes, in addition to allowing them to take control of the cell for proliferation, making it not work properly.