Viruses are tiny living things that can only be seen with powerful microscope.Viruses cause diseases.
Scientists have long sought to uncover the structure and function of viruses. Viruses are unique in that they have been classified as both living and nonliving at various points in the history of biology. Viruses are not cells but non-living, infectious particles. They are capable of causing a number of diseases, including cancer, in various different types of organisms.
Viral pathogens not only infect humans and animals, but also plants, bacteria, protists, and archaeans. These extremely tiny particles are about 1,000 times smaller than bacteria and can be found in almost any environment. Viruses can not exist independently of other organisms as they must take over a living cell in order to reproduce.
Virus Anatomy and Structure
A virus particle, also known as a virion, is essentially nucleic acid (DNA or RNA) enclosed within a protein shell or coat. Viruses are extremely small, approximately 20 - 400 nanometers in diameter. The largest virus, known as the Mimivirus, can measure up to 500 nanometers in diameter. By comparison, a human red blood cell is around 6,000 to 8,000 nanometers in diameter.
In addition to varying sizes, viruses also have a variety of shapes. Similar to bacteria, some viruses have spherical or rod shapes. Other viruses are icosahedral (polyhedron with 20 faces) or helical shaped. Viral shape is determined by the protein coat that encases and protects the viral genome.
Viral Genetic Material
Viruses may have double-stranded DNA, double-stranded RNA, single-stranded DNA or single-stranded RNA. The type of genetic material found in a particular virus depends on the nature and function of the specific virus. The genetic material is not typically exposed but covered by a protein coat known as a capsid. The viral genome can consist of a very small number of genes or up to hundreds of genes depending on the type of virus. Note that the genome is typically organized as a long molecule that is usually straight or circular.