Both bacteria and viruses fall under the group `micro-organisms' meaning `living creatures which cannot be seen by naked eyes.' The other groups of micro-organisms include fungi, algae and protozoa. Bacteria are of the size 10{+-}{+3} mm in diameter where as viruses are still smaller, 10{+-}{+4} _ 10{+-}{+5} mm in diameter. Bacteria are unicellular organisms in the sense that their entire body is made up of a single cell.
But unlike other living organisms viruses are acellular creatures, i.e., they don't have a proper cellular organisation. They appear like nonliving particles composed of nucleic acids (the genetic material), proteins and in some cases lipid layers. Viruses lack the ability to synthesize proteins and other cellular materials on their own because of their simple structural organization.
But unlike other living organisms viruses are acellular creatures, i.e., they don't have a proper cellular organisation. They appear like nonliving particles composed of nucleic acids (the genetic material), proteins and in some cases lipid layers. Viruses lack the ability to synthesize proteins and other cellular materials on their own because of their simple structural organization.
The viral particles usually remain inactive and need living systems for their growth and multiplication.
Bacteria can be cultured in laboratories artificially using synthetic chemical preparations called `medium.' But none of the viruses can be grown in artificial media and instead can be grown either in living cells or in living animals or plants. Because of this requirement of living systems, viruses almost always cause diseases in hosts.
A few examples of viral diseases are AIDS — caused by the virus HIV, polio — caused by poliomyelitis virus, rabies — caused by rabies virus, etc. Interestingly, viruses which cause diseases in animals won't cause diseases in plants and vice versa.
The above examples are diseases of human beings. Mosaic diseases are common plant diseases caused by viruses. Though bacteria don't require living systems they too cause diseases in animals and plants.
Typhoid, cholera, and diphtheria are examples of bacterial diseases caused in human beings.
Bacteria like most of the other living organisms have DNA as the genetic material while viruses can have either DNA or RNA as their genetic material.
Published in The Hindu on June 13, 2002.
