What is Viruses ?
Viruses are microscopic obligatory intracellular particles that must infect and take over a host cell in order to proliferate. They can only be observed under an electron microscope.
Scientist involved in discovering of viruses are :
- Two scientists Dimitri lwanowski and Martinus Biejernick played a crucial role to discover viruses.
- Loeffler and Frosch were are able to discover the first animal virus.
- Frederick Twort and D herelle discovered bacteriophages (bacteria eating viruses).
- Wendell Stanley for the first time crystallized virus (TMV).
The viruses are made up of only two components
- Protein (capsid)
- Nucleic acid (viral genome).
Some Important Points About Virus are:
Virus cannot survive and multiply outside the host cell.
The viral genome is protected against chemical and physical damage by the protein coat of the virus particle called capsid.
The capsid and the viral genome are together called the nucleocapsid.
The building blocks of capsid are protein subunits calles capsomeres.
On the viral capsid, special capsid protein called Spikes are present are binding sites of the virus so that it can attach to specific receptors on the host cells.
These capsomeres are responsible for the three different symmetry group of viruses are: icosahedral , helical and complex symmetry.
In some viruses with conventional icosahedral or helical structure, the nucleocapsid is surrounded by a flexible loose-fitting membrane made up of proteins and lipids which are acquired from the host cell during replication known as the viral envelope and such viruses are called animal of enveloped viruses. Viruses which do not have an envelope are called naked virus or non enveloped virus.
The viral nucleic acid are genome is made of either Deoxyribonucleic Acid (DNA) or Ribonucleic Acid (RNA).
Viruses with DNA as their genetic material are called DNA viruses and viruses with RNA as genetic material are called RNA viruses.
The DNA and RNA viruses are further subgroups in 7 classes.(Baltimore classification)
T- phages (T1 through T7; T standard for type) are a specific class of large Complex bacteriophages with icosahedral heads , double stranded DNA with the characteristic head and tail structure.
Tobacco mosaic virus has a helical symmetry with positive sense(+) single-stranded RNA in the middle.
Viruses are economically important as they cause losses from diseases and play a major beneficial role in medicine Research and diagnostics.