A virus is a microscopic infectious agent that can only replicate inside the living cells of an organism. It's essentially a package of genetic material (either DNA or RNA) encased in a protein coat. Unable to reproduce on its own, a virus invades a host cell, hijacking its cellular machinery to create more viruses. This process can lead to illness in the host organism.
Understanding Viruses: Key Characteristics
- Microscopic Size: Viruses are much smaller than bacteria and are only visible with an electron microscope.
- Obligate Intracellular Parasites: They absolutely require a host cell to replicate; they cannot reproduce independently.
- Genetic Material: Viruses contain either DNA or RNA, but never both, as their genetic blueprint.
- Protein Coat (Capsid): This protective protein shell surrounds and protects the viral genetic material. Some viruses also have an outer lipid envelope.
- Host Specificity: Viruses generally infect specific types of cells or organisms. For example, the influenza virus infects respiratory cells in humans, while the rabies virus affects nerve cells. There is some variation, with some viruses being able to infect multiple species.
- Infection Process: Viruses infect cells through various mechanisms, typically involving attachment to the host cell's surface and entry into the cell, where the viral genetic material is released.
Examples of Viruses:
- Influenza virus: Causes the flu, characterized by respiratory symptoms. (Source: THE BIOLOGY OF INFLUENZA VIRUSES)
- Chikungunya virus: A mosquito-borne virus causing fever and severe joint pain. (Source: Biology and pathogenesis of chikungunya virus)
- Hepatitis B virus: Affects the liver and can cause both acute and chronic infections. (Source: Hepatitis B virus biology)
- SARS-CoV-2: The virus responsible for the COVID-19 pandemic. (Source: Coronavirus biology and replication)
Several sources define a virus as an infectious microbe consisting of a segment of nucleic acid (either DNA or RNA) surrounded by a protein coat. (Source: [Definition](Definition. 00:00), Virus, What Are Viruses?). They emphasize the inability of viruses to replicate independently, requiring a host cell for reproduction. (Source: Intro to viruses, Virus). Viruses infect a wide range of life forms, including animals, plants, and bacteria. (Source: Virus | Definition).
