The 5 types of viruses, and how they work

When talking about living beings, no kind of discussion is generated when indicating that an animal or a plant is. The same is true for fungi, algae, and bacteria. But when it comes to viruses, things change. And it is that these infectious agents break the rules.

First, they are not cells, but rather simple protein structures that house genetic material inside. Second, its only way to reproduce is by infecting cells, to use its tools for this purpose. And third, they do not need to obtain any kind of energy, since they do not require maintenance.

Outside of the discussion of considering them living beings or not, there is variety both in their content and in their structures, which has allowed us 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. Better knowledge helps to prevent and treat these.

• Related article: "Major cell types of the human body"

Basic structure of a virus

Viruses stand out from anything because they are very 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.

Capsid

The main structure that all viruses have is the capsid. Formed by a set of protein units called capsomeresWhen the genetic content is stored inside it, it is called a nucleocapsid. The form this piece takes is one of the criteria for identifying types of viruses.

The nucleocapsid can present an icosahedral symmetry, which is observed as a spherical shape; a helical symmetry, which is rod-shaped or tubular; and complex symmetry, apart from the nucleocapsid, it has a protein structure that is called as a whole as a queue, which acts as a support to facilitate the insertion of content in a Guest.

Envelope

Regardless of this, some viruses may have a second layer, called the envelope, which is made up of 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, making it a good point to use in taxonomy. Roughly, 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

The types of DNA viruses have a small chain of nucleic acids which can be both single-stranded and double-stranded, that is, in one chain or in two. In addition, it can be circular or linear, it all depends on what virus we are talking about. They are the most common viruses to find. For example, the causative agent of herpes (Herpesviridae) has genetic content that is in the form of linear double-stranded DNA.

RNA virus

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

• Related article: "Differences between DNA and 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. Thanks to this, it can be used as a criterion for its classification. In this case, it focuses on who is your guest, having three groups:

• Animal viruses.
• Plant viruses.
• Bacteriophage viruses (they attack bacteria).

The case of coronaviruses

Recently, the term "coronavirus" has become world famous in the wake of the global pandemic caused by one of the virus species belonging to this category. It is the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), which causes the disease called COVID-19, pneumonia with a relatively high mortality rate in humans. This variant of the pathogen was discovered in the Chinese city of Wuhan, but from this point of origin, it has mutated several times.

But beyond this case, coronaviruses are types of viruses known for a long time and that in the taxonomy used to classify these biological entities are in the family of the Coronaviridae, so it is considered that they constitute a subfamily.

One of its characteristics of these species is that are RNA viruses with a longer genome, and by the protrusions of its rounded surface, which make that seen by the microscope appear to wear a crown with points. On the other hand, most coronavirus species do not pose a significant danger to most people.

How do they work?

He couldn't finish this article without explaining how viruses work in a generic way. The virón (mature form of the virus), locates a host cell, managing to introduce its genetic content inside. This material inserts itself into the DNA of the nucleus, so the cell can transcribe its information and translate it into 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 capsids and form new virons that leave the infected cell.

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

The cause of viruses causing disease is due to this insertion into the cell's DNA, which can translocate genes, in addition to allow them to take control of the cell for its proliferation, causing it to not work correctly.

Bibliographic references:

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• Pennisi, E. (2011). Going Viral: Exploring the Role Of Viruses in Our Bodies. Science, 331 (6024): 1513.
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