A virus is a submicroscopic transmissible agent that replicates inside the living cells of an organism. Viruses infect all kinds of life forms, from plants and animals to microorganisms, including archaea and bacteria.
Viruses do not have a solid membrane as all other cells do and rely solely on host cells to survive. Viruses can be considered sub-cellular parasites that infect living cells and then take over the cell’s metabolic means to compose more viruses. Viruses are not cells, but they carry enzymes characteristically located only in living cells.
Technically, a virus is not a living organism. It is really a protein box that holds a tiny strand of nucleic acid – a core found in the nuclei of living cells. Viruses come in numerous sizes and shapes. Viruses are so small., you can only see them using an electron microscope.
Of all the features of living things, feeding, movement, excretion, respiration, sensitivity, growth, and reproduction, only reproduction is relevant. Viruses do not reproduce in the sense that cells do because new viruses do not originate from pre-existing viruses. Outside of the host, viruses are inactive and inert, and viruses can be crystallized and isolated like a chemical compound. Only in a pure genetic sense can one think of a virus as a living thing since a virus can absolutely control the genetic make-up of the following ‘generation’ of virus particles.
Viruses cause disease. A virus may lie inoperative for many years, yet an unusual thing happens when it comes in contact with a fit living cell. The small virus particle ‘hijacks’ the host cell and ‘pushes’ it to make hundreds of copies of itself. Eventually, the host bursts open, and the cell dies. The newly created virus particles immediately escape and go on to contaminate other cells. Among the many conditions caused by viruses are polio, smallpox, influenza, measles, chickenpox, and colds
Medically, virus infections are challenging to treat. Antibiotics are of no use against them. Immunization is often the only defense against severe viral diseases.
The steps involved with the virus ‘hijacking’ the host cell are:
- The virus attaches itself to a fit host cell. It injects its nucleic acid into the cell.
- The nucleic acid takes charge of the host cell. The cell stops its own activities and begins making only nucleic acids and virus protein coats.
- The protein coats and the new nucleic acids join together to form hundreds of accurate replicas of the initial virus inside the cell.
- About thirty minutes after being infected, the host cell may open and set free the new virus shreds.
Here are few interesting facts about viruses
- There are a million viruses per milliliter of seawater – for a total of 1030 virions!
- The basic genetic information of viruses can be RNA or DNA, one or double-stranded, a single molecule, or in pieces.
- Viruses are not alive outside host cells. They can only harm when they’re inside a host.
- The largest known viruses are mimiviruses, which are 0.0004 millimeters (400 nanometers) in diameter, whereas the smallest are circoviruses, which are 0.00002 millimeters (20 nanometers) in diameter.
- Researchers suspect that a sizeable DNA-based virus took up shelter inside a bacterial cell millions and billions of years ago to build the first cell nucleus. If this research is correct, then viruses are our actual ancestors.