Mr. C’s Top Ten Questions About Virus
Question One: Are Virus living things?
Non living Characteristics
Living Characteristics
they do not respire
they do have DNA or RNA
there is no cellular structure
they do have proteins and enzymes
they do not grow
they have the potential to make other cells make copies of themselves, this is more like duplication than reproduction
they can be crystallised due to harsh environments
virus show diversity associated with the hosts they infect
they cannot reproduce on their own
* this is a great table for a test question….
Question Two: What are virus and where did they come from?
Virus may be linked to the original entity of life as a noncellular ancestor of cells
Their means of existence may imply that they were once primitive organisms that loss cell structures in order to assist parasitic lifestyle.
The genetic material within a virus is only a fragment of an original genome.
Question Three:
What is the structure of a virus and how is it associated with its lifestyle.
Most virus are composed of a protein coat which surrounds a small fragment of DNA or RNA.
Most virus are only visible with electron microscopes ranging in size from .015 to .45 microns.
Some of the protein coats are specialised for the host that the virus infects.
The shape of the protein coat may vary from spherical shapes to bacteriophage which have additional structures to add attachment to host.
Shapes are usually spherical, rod shaped or tadpole shaped.
Question Four: How are virus classified?
Virus are classified by the host they infect
Plant virus: ( example tobacco mosaic virus)
Animal ( by class: Aves : Bird, Insecta: insects) virus
Bacteria virus or Bacterio phage
Question Five: How are virus transmitted?
In plants: virus can be transmitted from contact with insects, direct contact between plant seeds, leaves or stems.
In animals: virus can be transmitted from coughing, sneezing, talking, direct contact and insects.
Question Six: How do virus infect host
A general infection follows the following pattern.
The virus comes in contact with host cell and attaches to host cell.
Viral Protein coat is either removed after absorption by host or virus injects nucleic material into host.
Viral DNA or RNA is replicated by the host cell.
Replicated viral DNA or RNA is translated into proteins for viral enzymes and protein coat.
New virus are assembled within host cell from replicated and translated material.
Virus either remain in host or host cell breaks due to too many virus within cell.
Specialised infections:
Bacteriophage: Virus that infect bacteria
In this type of infection there is the possibility of two events
a) A lytic cycle
Virus attaches to host bacteria, an enzyme eats away the host’s cell wall and viral nucleic material is injected into host
Viral nucleic material is incorporated into host nucleic material
Viral nucleic material begins to replicate and translate its code, this takes over the bacteria normal cellular functions.
As many as 100 or more copies of the original virus are made by host bacteria
The host bacteria burst and virus is release to the environment. The word lytic comes from the Latin which means to burst open
b) A lysogenic cycle.
Much like the lytic cycle the host bacteria is infected by the virus, however lyses of the bacteria does not happen immediately. Bursting of the cell only occurs when the bacteria become weakened or there is a change in the environment.
c) Mutagenic
some virus will not cause the cell to lyse or die but will cause mutations which can change the growth rate of the cell or the shape and size of cells. Some of these viruses have been linked to creating cancer cells. Remember…one of the characteristics of cancer cells are their growth rate and change is morphology.
Retrovirus Infections:
A retrovirus is a RNA virus which infects the host in a unique fashion.
The viral RNA serves as a template for the host cell to make a segment of DNA.
This DNA is then encoded into the host’s genetic material.
The cell does not die but changes due to the new encoded material.
The mechanisms of this type of infection are still being researched.
Question Seven: Are all infections the same?
The answer is no. There are at least three possible outcomes from an infection:
Results of viral infection can be:
A virulent infection:
This is when the virus causes a lytic cycle and the host cell dies
A latent infection:
This is when the virus either becomes part of host genome or remains dormant until changes in host cell and or external environment.
Tumour producing infection:
This is when the host cell is not destroyed but mutated causing the host cell to divide and produce cluster of cells that have changed from the original cell. If these cells remain dormant they are said to be benign and show themselves as a wart or tumour), if these cells become mobile, they are said to be malignant.
Question Eight: What diseases are caused by viral infections?
Some common viral infections are:
viral pneumonia, the common cold, influenza, mumps, measles, German measles polio shingles chickenpox smallpox, AIDS virus hepatitis warts yellow fever cold sores hoof and mouth disease Ebstein Barr virus mosiacs in plants
May be associated with some cancers, leukaemia’s, and autoimmune disorders
Some lethal viruses: Ebola (95% fatality rate)
Most publicised virus: HIV
Question Nine: Is there a way to treat or cure viral infections?
One of the first methods of preventing infection by virus was done by the Chinese, who rubbed other individuals with skin scabs from those individuals who survived a viral infection such as small pox.
Edward Jenner, created a process called vaccination ( from the Latin origin vaca for cow : another famous cow story!) by exposing individuals to cowpox virus, which he noted prevented them from being infected from a more virulent virus for small pox.
It is useless to treat a viral infection with antibiotics however people treated with a killed strain of virus or viral proteins may create their own antibodies to attack onto viral proteins.
Question Ten: How were virus discovered?
Discovery of virus were initially related to nature of infection of hosts
Actual viral material viral material was not purified until 1933 by Stanley. This particular material was crystallise tobacco mosaic.
Identification of viruses has improved with the increased efficiency of electron microscopes.
Because viral DNA/RNA interacts with host nucleic material, viruses are continue to change and evolve.
If you have any further questions you wish to explore…contact Mr. C
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