What are viruses ?
Virus infections are universal. Viruses are all around us in the environment, they can contaminate our food and as a result, the presence of the virus in contaminated food gains entry into the GI tract and then it might cause gastroenteritis or other infections.
Viruses also present around us in the environment,it present in the soil, air,etc… good examples here are respiratory viruses, we have many known respiratory viruses such as ( influenza virus – it causes flu- , corona virus, rhino virus, mumps, measles ).
Viruses are nucleoprotein entity but it’s able to utilize the machinery of a living cell of another organism for it’s multiplication, (non-cellular organisms), they have inert crystalline structure outside the living cell and that’s why they don’t grow or divide if they are out side the host organism.
Once they infect a cell they take over the machinery of that host cell and replicate and resulting in killing the host. So that’s why they are involved in various plants and animals and human diseases.
How they were discovered?
Virus word means venom or poisonous.
In 1892, Dmitry Ivanovsky discovered virus in “tobacco”, he noticed that diseased tobacco plants infect the healthy tobacco plant. And this discovery was the beginning of virology.
In 1935 Wendell Stanley discovered that viruses could be crystallized and these crystals are basically proteins.
In 1949 John Franklin Enders, Thomas Huckle Weller and Frederick Chapman Robbins cultured the polio virus successfully and received Nobel prize for that.
A Virus is an obligate intra-cellular parasite or organism, containing genetic material surrounded by protein.
Obligate organism means that the virus is not a living entity by itself, it requires a living host cell in order to grow and replicate itself.
Now, the virus containing genetic material (core of nucleic acid) which might be either DNA or RNA, but NEVER both like other cells, this genetic material is surrounded by a protein coat which is called capsid.
viruses have different sizes and shape . the average size of the virus is within 20-450 nano-meters , that’s why the viruses can only be observed via electron microscope.
Why viruses are nonliving entities by themselves and they require a host cell?
Viruses don’t have the organelle necessary for protein synthesis which is the ribosome. So, all viruses require the cellular ribosomes in order to synthesize and replicates their proteins; whether structural or non-structural proteins.
What do we mean when we say structural and non-structural proteins?
- Structural proteins: are proteins which play a role in making up the virus. Such as the capsid protein that surrounds the genetic material, and glycoproteins which are embedded within the envelope in the enveloped viruses.
- Non-structural proteins: are enzymes which are synthesized by viruses.