Overwhelming majority of organisms existing on the Earth consists of cells and only viruses don’t have any cellular structure.
According to such prime criteria all living things are divided nowadays into two empires:
- -pre cellular (viruses and phages)
- -cellular (all the rest organisms: bacteria and close groups to them - fungi, plants, animals and human beings).
Viruses are the tiniest organisms, their sizes range from 12 to 500 nanometers. Small viruses are equal to large protein molecules. Viruses are pronounced parasites of the cells.
These are the most important differential virus characteristics:
- Viruses contain only one nucleic acid: ribonucleic (RNA) or deoxyribonucleic acid (DNA) while all of the cellular organisms, including the most primitive bacteria, contain both DNA and RNA.
- Viruses don’t posses their own metabolism, they have very limited amount of enzymes. For their duplication they use host-cell’s metabolism, its enzymes and energy.
- Viruses can exist only as intracellular parasites and can not multiply without organism’s cells on which they parasite.
The most primitive viruses consist of RNA (or DNA) molecule, surrounded by protein molecules that make a viral envelope. Some viruses have one more coating– an external or secondary shell; more complicated viruses contain number of enzymes.
Nucleic acid (NA) is a genetic information carrier. Proteins of internal and external envelopes serve as its defenders.
Thus as viruses don’t posses their own metabolism outside of the cell they exist as “nonliving” particles. In this case one can say that viruses can be corresponded to the inert crystals. As soon as viruses get into the cell they revive.
During reproduction viruses use nutrients and energy-metabolic systems of the infected cells to generate compounds of viral particles. When virus is penetrated into the cell it dissolves into components – NA and envelope proteins (something like“stripping”). Since that moment host-cell bio-synthetic processes are commanded by genetic information of the viral nucleic acid.
In the host-cell synthesis of discrete viral envelope and NA is carried out. Later on they cooperate and form a new virion (a completely formed mature virus). The scientists noted that peculiarity and even conducted the following experiment. They split mosaic tobacco virus into two components: NA and protein. After that they mixed components together and … got the viable initial virus with all its biological properties. As we know, cells are multiplied by division. Splitting of the cell into components (nucleus, envelope, cytoplasm, mitochondria, ribosomes) and then mixing all the parts together won’t lead to the similar effect – a cell will not be regenerated. Viruses are not reproduced on the manufactured nutrient medium – they are too intelligible in nourishment. Ordinary meat broth that fits most bacteria doesn’t suite viruses. They need brisk cells and strictly specified.
Scientists know viruses of bacteria, insects, animals and human beings. In all, there are more than 1000 of them. Usually but not always processes connected with viral duplication damage and destroy a host-cell. Viral reproduction, coupled with cells destruction, leads to diseased states of the organism. Scientists established that there are many various viruses in the human body but they don’t always approve (reveal) themselves. Pathogen virus impacts only on the weakened organism.
There are many different ways of viral infection: via skin during insect and tick bite, via saliva, slime (mucin) and other afflicted persons secretions (discharges); via air; with food, sexual intercourse and others.
Viruses cause murrain, plague, bate in animals,Fast and severe polyhedrosis and granulomatoFast and severesis in insects, in plants - mosaic and other leaves changes: flowers color, leaf-curl mosaic and other changes in shape, dwarfism; at last in bacteria – their destruction.
At the very beginning viruses were considered to be causative agents of diseases only. The idea of viruses as the solely pathogenic nowadays prevail in a wide circle of “outsiders”. However it’s not quite correct .
It is known that number of viruses are not account for illnesses. Many of them penetrate into the human organism but don’t cause any clinically detectable diseases. They can exist in the host cell without any external demonstrations for a long period (e.g. stells viruses).
The idea of viruses as of unstoppable “destroyers” was preserved during investigation of a special viral group – viruses that attack bacteria. We are talking about bacteriophages (so-called phages) that were discovered in 1917 in France and England at the same time. People hoped that the ability of phages to destroy bacteria could be used for the treatment of diseases caused by those bacteria.
And phages really appeared to be the first “hand-reared” viral group. They destroyed their neighbors in the microworld rapidly and severely. Bacilli of plaque, typhoid, dysentery, cholera (comma bacillus) quickly disappeared after meeting those viruses. People began to use them as prophylaxis and for treatment of many infectious diseases, but unfortunately the first success was followed by failures. It was connected with less active bacterial attack of phages in the human body compared with their activity in the test tube. More over, bacteria turned out to be more “artful” than phages and quickly adapted to the phage action and became inert to it.
After antibiotic discovery phages as a medicine receded into the background but they are still used for bacteria identification. The matter is phages are able to find “their bacteria” and quickly dissolve them. Such phage capacity lied in the base of therapeutic diagnostics. Usually it is done like this: bacteria from afflicted person are grown on the nutrient stiff agar medium, after that different phages, for example dysentery, typhoid, choleric, are applied to the bacterial “lawn”. In a day Petri dishes are viewed through the light and define which phage has caused lysing of bacteria. If that action was made by dysentery phage it meant that dysentery bacillus was isolated from afflicted human’s organism, if it was done by typhoid phage – by the typhoid bacillus.
Sometimes viruses that attack animals and insects help people. More than twenty years ago in Australia people faced a big problem with wild rabbits. Number of those rodents reached menacing extents. They ate crops faster then grasshopper did and became a real national disaster. Ordinary methods to control their quantity were ineffective. And than scientists released special virus capable to kill nearly all infected animals to check rabbit population. But how could they spread this disease among timid and careful animals? Mosquito did (helped). They served as flying needles, delivering virus from one rabbit to another one. At the same time mosquitoes were absolutely healthy.
What will happen to the cell if it is infected not with one but with two viruses? If you consider that in this case cell’s illness recrudesces and its death will accelerate, you are wrong. It turned out to be that the availability (presence) of one virus in the cell often protects it against the destructive activity of another one. Such a phenomenon was called by scientists as virus interference. It’s connected with the development of a special protein – interferon that activates protective mechanisms able to differentiate viral from non viral and selectively suppress the second one. Interferon suppresses duplication of the most if not all viruses in the cells.
Developed as medical preparation interferon is used for treatment and prophylaxis of many viral diseases.
What kind of useful things can be expected from viruses in future? First of all it's necessary to remind of gene engineering. Viruses can help to the scientist - capture appropriate genes from one cell and carry them to another one.
At last there is one more opportunity of viruses use. Scientists discovered a virion capable to destroy selectively some mice tumor. Viruses which can kill human cancer cell are obtained as well. If one can succeed to deprive these viruses from their pathogenic properties and to preserve their ability to destroy malignant tumor selectively, the intensive and efficient remedy against these severe diseases will be invented (developed) in the future.
The process of searching after such viruses is going on and nowadays the research doesn’t seem to be so fantastic and hopeless.
