Viruses are microscopic beings made up of DNA or RNA and protected by a layer formed of proteins.
They are considered intracellular parasites and, therefore, their functions can only be performed when they enter a host cell to use all its resources.
Virus Structure
Viruses are formed by nucleic acids, RNA (ribonucleic acid) or DNA (deoxyribonucleic acid), surrounded by a protein layer called a capsid. In addition to these components, some viruses can still be coated with a film of fat and protein.
- Nucleic acids (RNA and DNA) : are the information contained in the virus that must be used to synthesize proteins in the invaded cell;
- Capsid : surrounds and protects viral nucleic acid from digestion by enzymes. In addition, it has regions that allow the passage of nucleic acid to inject into the cytoplasm of the host cell;
- Glycoprotein envelope : coating formed by lipids and proteins around the capsid, which are used to invade the cell membrane and bind to it, facilitating the fixation of the virus.
Virus characteristics
The main characteristics of viruses are:
- They are acellular beings, that is, they do not have cells;
- Its dimensions range from 17 nm to 300 nm;
- They are diverse beings and therefore do not have a pattern;
- They are capable of mutating;
- Outside a host organism they crystallize like minerals;
- They do not have their own metabolism and, therefore, reproduction occurs in a living cell.
Much is discussed about whether viruses are considered living beings or not. While for some scholars they are just infectious particles, for others, once they reproduce and undergo genetic mutations, they are included in the category of living beings.
Types of Viruses
Viruses are classified according to the type of nucleic acid, according to the shape of the capsid and also by the organisms they are capable of infecting. See the examples below.
- Adenovirus : formed by DNA , for example the pneumonia virus.
- Retroviruses : formed by RNA , for example the HIV virus.
- Arbovirus : transmitted by insects , for example the dengue virus.
- Bacteriophages : viruses that infect bacteria.
- Mycophages : viruses that infect fungi.
Important information about viruses is that they can use transmitting agents in an infection. For example, plants can be infected by viruses through insects or other organisms that feed on them.
Reproductive Cycle
Viruses are able to invade different types of cells, mainly bacteria, plants and animals.
In the reproduction cycle, viruses usually break the cell wall, enter, replicate and leave to infect new cells.
There are also viruses that do not need to enter a cell to reproduce, they just inject their genome into the host cell.
Viral genetic material inserted into a cell is translated and replicated as the cell multiplies.
Generally, viruses use the ribosomes of eukaryotic cells to translate the messenger RNA they saw and thus produce viral proteins within the cell.
The reproductive cycle of these organisms can then be divided into 4 stages:
- Entry of the virus into the host cell;
- Eclipse (virus inactivity);
- Multiplication of viral material (copies of the matrix);
- Release of new viruses.
In other words, in the virus reproduction process, there is a duplication of viral genetic material and protein synthesis as it inhibits the normal functioning of the cell.
Diseases Caused by Viruses
Diseases caused by viruses are called viruses. Check out some examples below.
Note that viruses can infect both the cells of animals, fungi, vegetables (eukaryotic), and bacteria (prokaryotic) and, in this case, are called bacteriophages.
How were viruses discovered?
Louis Pasteur (1822 – 1895) was the first to use the term virus to explain what would be the causative agent of rabies disease. The filtration technique was his ally in this discovery, since the filter used retained bacteria and allowed even smaller beings to pass through.
In 1892, the disease-causing virus in tobacco leaves was characterized by the botanist Dmitry Ivanovski (1864 – 1920). Studying the same plant, in 1899, the botanist Mariunus Willen Beijerinck (1851 – 1931) managed to transmit the disease to a healthy unit. Between 1915 and 1917, viruses that “eat bacteria” were discovered.
Although important discoveries occurred, until the 20th century the nature of viruses was not understood.
The study of microscopic beings, such as viruses, became possible with the invention of the microscope. In addition, advances in cell culture in the laboratory and advances in the field of genetics have made information about viruses dramatically improved.
We have more texts for you on the subject :
- Microbiology
- What is an epidemic?
Curiosities
- The Latin word “virus” means toxin, poisonous fluid.
- The term “computer virus” came about by analogy to the biological virus marked by its parasitic characteristic.
- The ” virion ” corresponds to the viral particle when it is outside the host cell.