Virus

Viruses are non-cellular infectious creatures that are very small and can only replicate themselves within the cells of a host. From a biological point of view, viruses cannot be placed in either the category of living beings or non-living organisms. This is because they share certain defining qualities with both living and non-living species, and these characteristics may be found in both of those categories. 

Definition of virus

A virus, in a nutshell, is an infectious non-cellular creature that is made of genetic information and protein. Viruses can only infiltrate and reproduce inside the live cells of bacteria, plants, and animals. For instance, a virus is unable to create offspring outside of the cell that it infects. This is because viruses do not possess the essential cellular machinery to replicate themselves. As a consequence of this, it enters and attaches itself to a particular host cell, injects the genetic material of the host cell, reproduces using the genetic material of the host cell, and then finally rips open, releasing young viruses. Crystallization is a process that is unique to viruses and cannot be carried out by any other living organism. As a result of these characteristics, viruses are placed in a category that may be conceptualised as being somewhere between living and nonliving entities. 

Types of virus structures

Viruses may be anywhere from 30 to 50 nanometers in size, making them very minute. They lack a cell wall but are protected by a protein sheath known as the capsid instead of having one. Viruses do not have a cell wall. It may be It is considered to be a genetic component, and its definition is determined by the mutual growth of the virus and the host. Either RNA or DNA is present in them as their genetic material. 

The complex metabolic machinery of prokaryotic or eukaryotic cells, which is required for viral replication, can only be obtained from a host in order for viruses to multiply. The fundamental objective of the virus is to deliver its genome, which might be made of DNA or RNA, to the host cell so that it can be transcribed. A protein capsule that is symmetrical surrounds the viral DNA and protects it. The protein that is coupled with nucleic acid is what ultimately results in the production of the nucleocapsid (also known as nucleoprotein). 

Properties of Viruses – 

• They are animals that lack cells and are encased in a cocoon for their protection. 
• The fact that spikes are present on the virus makes it easier for it to attach itself to the host cell. 
• These viruses do not multiply, do not expand, do not respire, and do not metabolise. 
• They are encased in something called a capsid, which is a protein shell, and they contain a nucleic acid core that is either DNA or RNA. 
• They are seen as both living and nonliving entities depending on the context. These viruses are in a latent state while they are outside of the cells of their hosts, but as soon as they enter the cells of their hosts, they become active. These viruses infect the host cell and then reproduce within the cell by making use of the enzymes and other components present. 

Classification of Viruses – 

The behavioural characteristics of viruses, as well as their core content, chemical composition, capsid structure, size, shape, genomic organisation, and replication methods, are the primary factors that are used to classify viruses. When doing research on viral categorization systems, the Baltimore classification system is applied more often than any other. This method was developed in the 1970s by an American researcher by the name of David Baltimore, and the Nobel Prize in Chemistry was bestowed upon him for his work. 

Classification based on the presence of nucleic acid – 

DNA virus 

DNA is the viral genetic material, which describes the virus. DNA viruses may be separated into two distinct groups. 

Picornaviruses, parvoviruses, and several other viruses that only contain a single strand of DNA are examples. 

Herpes virus, adenovirus, and other viruses with double-stranded DNA such as these 

RNA virus

RNA is the viral component that contains the genetic information. The RNA virus may be split into two different groups. 

One example of this kind of virus is the reovirus, which has RNA that is double-stranded. 

RNA virus consists of just one strand (ss). The two varieties of RNA are referred to as positive sense RNA, or +RNA, and negative sense RNA, or -RNA (-RNA). The poliovirus, the hepatitis A virus, the rabies virus, and influenza virus are all examples of viruses that contain a single strand of RNA. 

Classification based on the structure or symmetry – 

• A virus that is complicated and difficult to comprehend. Poxvirus, for example. 
• Virus that has radial symmetry. For example, a bacteriophage 
• Viruses that have icosahedral or cubic symmetry. Such viruses include the Reovirus and the Picornavirus. 
• Viruses that have the shape of a rod, a spiral, or a helical. 
• Examples of this would be paramyxoviruses and orthomyxoviruses. 

Classification based on the replication properties and site of replication –

This is the point at which viruses enter the host cell; once inside, they proceed to proliferate and assemble themselves inside the organelles of the cell. 

Classification based on the host range 

According to the species of host, there are four primary categories of viruses. : 

Viruses in animals 

The infiltration of these viruses into the cells of animals, including humans, results in infection. Examples of animal viruses include the influenza virus, the mumps virus, the rabies virus, the poliovirus, and the herpes virus, amongst other viruses. 

Viruses that infect plants 

These viruses infect plants by invading the cells of the plants themselves. Well-known examples of plant viruses include the potato virus, the tobacco mosaic virus, the beet yellow virus, the turnip yellow virus, the cauliflower mosaic virus, and other plant viruses. 

Bacteriophage 

There is a class of viruses known as bacteriophages, and they infect bacterial cells. Bacteriophages are available in a wide range of forms and configurations, such as DNA viruses, MV-11, RNA viruses, Page, and many more. 

Viruses infecting insects 

Viruses that infect insects are referred to as insect viruses. Insect viruses are also widely referred to as the viral pathogens of insects. It is believed that these viruses may act as effective biocontrol agents in the agricultural environment that exists now. Insect viral examples include Asco virus virions and Entomopox virus. 

Conclusion  

Not only are viruses common, varied, and essential to ecosystems, but they also play a significant part in the growth and development of the organisms that they infect. In addition to the selective pressure that they exert on cell populations, they also contribute to the evolution of genes and genomes and the movement of genes across lineages.