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Viruses

posted Jan 27, 2015, 10:31 PM by Ranmini Perera   [ updated Sep 9, 2017, 4:17 PM by Upali Salpadoru ]






Fig.1 A diagram showing a section of a virus 


"Oh! Don't worry. It's only a viral attack." 

A GP would have diagnosed a sickness. 

All readers must be quite familiar with the term 'Viruses' but do you know what they are? 
 Some of the knowledgeable would say "Yes we know"
 Then you are probably wrong. Nobody seems to know 'What they are'.
 According to the modern classification of living things, viruses are not included. They lack some of the basic qualities of the living and are unable to carry out some basic physiological functions..

Viruses are defined as microscopic particles (30 t0 300nm; 1nm = 10-9 ) containing DNA or RNA. within a cover of protein. A bacteria is 100 times bigger than this. They cannot be
seen through a light microscope.

Viral Diseases.

All varieties of flu and  poxes, raging from chicken pox to small pox and such terrible diseases as polio, rabies and AIDS are caused by viruses. Dengue and Chickengunya are acute viral diseases transmitted by the mosquito Aedes Aegypti. There are many varieties of the same disease, so an infection of one type will not produce immunity for others. That’s how we get flu so many times.


Dengue starts off with a headache and soon, fever, muscular aches and joint pains arise and rashes appear. There may also be abdominal pain nausea and diarrhoea.  The disease is not directly infectious. At the end of the fever platelet count drops. Platelets are the cell fragments circulating in the blood that are involved in the repair of blood leaks from the capillaries . So a low platelet count will lead to internal bleeding.

The latest is the Ebola virus.

Fig.2  The diagram shows a phage attacking E-coli.

Viruses gain entry into living cells and use up the cell contents to make its own type of living matter. Then they multiply and escape to infect more living cells of the host. Some viruses readily attack bacteria. They are known as bacteriophages.

Treatment for Viral Attacks

In case of a bacterial infection, your doctor can prescribe anti biotics. What can he give for a viral attack? He’ll say “ Viruses are not biotic; anti-biotics wont do.” In the 18th Century Mary Montague , an English lady observed in Constantinople, local women blowing small pox crusts into  the nostrils of their children. This process came to be known as ‘inoculation’. Edward Jenner observed Miss Sarah Nelmes , a milk maid who had previously caught cow-pox was immune to small-pox. Even today  the only way to fight viruses is to build up immunity. When a person gets a viral attack the body makes anti-bodies which can counteract the invader. This is why we normally don’t get the same infection twice.

Are they Living

There is no definite answer to this. It all depends on how you define life. Viruses do not have cells. They only contain nucleic acid, (DNA, RNA) which are capable of carrying out physiological functions only  inside a host  cell. A plus factor for the argument is that they are capable of making copies of their type of nucleic acid.Viruses are not the only dwellers between the living and the non living. There are the PRIONS, (Proteinaceous Infectious Particles)   that lack nucleic acid. When these gain entry into the living cells they behave just like viruses. Viroids are another group that cause disease in plants. They consist of a strand of RNA only.

Origin
One hypothesis is that they have undergone reverse evolution due to a parasitic way of life. Cells and some of the contents may have degenerated as they were not being used.
Another view is that they may have been formed by some run away parts of nucleic acid which have got detached from the genes of higher animals and plants.
A third possibility is that they were the pioneers of life.

Comparing Microbes


BACTERIA

FUNGI

VIRUS

1.Movability.

2 Sensitivity.




3.Nutrition.




4.Respiration.







5. Growth.






6.Cells.






7.Reproduction.





8.Excretion.

Some can crawl using pili or even swim using flagella.

They are sensitive to changes in heat, light, nutrients and chemicals.

They secrete enzymes into the food and absorb the nutrients selected by the cell membrane.

Some bacteria use Oxygen just like other organisms. There are others that derive energy  using other chemicals such as su;phur and iron. Some bacteria are capable of fermenting sugar.

As a result of taking in food and building up the body matter the cells grow in size.


Bacteria  cells are surrounded by a cell wall and a cell membrane. They carry nuclear material though not enclosed by a membrane.(Prokaryotic cell)

Matured bacteria reproduce by binary fission.(Asexual)

Some undergo conjugation.(Sexual)

They excrete waste produced due to reactions inside the cell mainly by diffusion.

Most fungi are incapable of any independent movement except for the growth movements.

They grow towards an area rich in nutrients and moisture..



They generally live inside the food. Digestive enzymes are secreted out and the nutrients are absorbed.

Fermentation is the general mode of respiration. Sugar is broken down to to produce alcohol and carbon dioxide giving energy.





The thallus makes body matter and elongates often producing branches.


The mycelium is surrounded by a cell wall made of chitin. In some species they are divided into units by septa.


Fragmentation is the norm.




Mainly by osmosis.

They do not show any movement except for their ability to push their DNA into a living cell.

They can sense the exact living cell in which they can grow.


A Viruses gets food from the host cell for reproduction.


As there are no metabolic activities, (reactions) without a host cell, there is no respiration outside.




These cells also increase in size.



The genetic material is covered with a protein coat called a capsid.





A virus has to enter a living cell to make copies of itself.



They pass any waste produced into the host cell.


   Bacteriophages are also a group viruses that attack bacteria. click: bacteriophages


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