General Characters of Viruses
Virology is a branch of science that deals with the study of viruses.
- Viruses are non-living characters, they are not cells.
- They do not have a cytoplasm or any kind of cellular organelles to carry out any kind of metabolism.
- Viruses are able to infect all living forms including plants, animals, human beings and even micro-organism.
- Viruses are Obligate intracellular parasites they require a living cell or organism for its multiplication.
- Viruses can be observed only under the electron microscope.
- They are 10 to 100 times smaller than bacteria and its size ranges from 20 to 300 nm so these viruses can pass easily through bacteriological filters. They are filterable.
- Size of viruses is measure with the help Ultrafiltration, ultracentrifugation and electron microscopy.
- Viruses do not have any kind of cellular organisation.
- Viruses have spikes which help the virus to attach on the host cell.
- It contains either DNA or RNA as a nuclear material.
- As we know viruses are an obligate intracellular parasite and lack the essential enzyme for protein and nucleic acid synthesis. These viruses depend on the host cell for its replication and multiplication.
- Viruses are unaffected by antibiotics, there are many differences between micro-organism and viruses in spite of that viruses are considered as micro-organism especially in the field of medical microbiology.
- Viruses are of great concern in the field of medical microbiology because they are responsible for various human diseases.
- Examples of diseases caused by viruses are Rabies, AIDS, Mumps, Hepatitis, Influenza, Dengue, common cold and many more diseases are caused due to viruses. Viruses are responsible for cancer in human beings, birds and animals.
- Viron is an extracellular infectious particle of the virus. Viron contains essential nucleic acid which is protected by the protein coat called as the capsid.
- The function of the capsid is to protect nucleic acid from nucleases and other environmental factors. The capsid is made up of polypeptide molecules.
- Capsid shows two types of symmetry that are cubical or icosahedral symmetry and helical symmetry. Icosahedral symmetry shows 12 vertices and 20 sides.
- The icosahedral contains two types of capsomers Pentons at the vertices and hexons at the Facets or sides
- Different viruses have different shapes, most of the animal viruses are roughly spherical in shape as well as pox virus is brick shape, TMV is rod shape etc.
- Viruses may be enveloped or non – enveloped.
- Envelop is made up of lipoproteins and is derived from host cell membrane.
- Viruses require a living media like the embryonic egg, cell culture or bacterial cells.
- There are two types of viruses that are DNA viruses and RNA viruses.