2. Viruses: complete virus particle
called virions are very small and
simple structure.Most viruses
range in size from 10 to 300 nm in
diameter although some like ebola
virus can be up to 1 nm in
length.The smallest virus is about
the size of the large hemoglobin
molecule of a red blood
cell.Viruses could not be seen until
electron microscope invented in
1930s.
3.
4. No types of organism is safe from vital
infect;viruses infect humans,animals
,plants,fungi,protozoa,algae,and bacteria.
5. Some viruses called
oncogenic viruses or
oncoviruses cause
specific typesof cancer
including human
cancers such as
lymphomas
carcinomas and some
type of leukemia.
6. Viruses are said to have five specific properties that
distunguish them from living cells.
*They posses either DNA or RNA unlike living cells
which posses both.
*They are unable to replicate (multiply)on their
ownn.Their replication is directed by the viral nucleic
acid once it has been introduced into a host cell.
*Unlike cells they do not divide by binary
fission,mitosis or meiosis.
*They lack the genes and enzymes necessary for
energy production.
*They depend on the ribosomes,enzymes and
metabolites(building blocks )of the host cell for
protein and nucleic acid production.
7.
8. Some viruses called enveloped viruses because they have
ana outer envelope composed of lipids,and
polysaccharides.Bacterial viruses may also have a
tail,sheath,and tail fibers.There are no ribosomes for
protein synthesis or sites of energy production ;hence the
virus must invade and take over a fuctioning cell to
produce new virions.
Viruses are classified by the ff.characteristic:
:type of genetic material (either DNA or RNA)
:shape of the capsid
:number of capsomers
:size of the caspid
:presence or absence of an envelope
:type of host that it infects
12. Two main theories have been proposed to explain the
origin of viruses.
First the theory state that viruses existed before cells, but this
seems unlikely in view of the fact that viruses require cells for their
replication.
Second the theory states that cells came first and that viruses
represent ancient derivatives of degenerate cells or cell
fragments..However most scientist agree that viruses lack most of
the basic features of cells,thus they consider viruses to be
nonliving entities.
14. The viruses that infect
bacteria are known as
bacteriohages.Like all
viruses they are obligate
intracellular pathogens in
that they must enter a
bacteria cell to replicate.
15. Three Categories of Bacteriophages based on their
shape:
Icosahedron
Bacteriophages:an almost
spherical shape with 20
triangular facets,the smallest
icosahedron phages are about
25 nm in diameter
18. Virulent Bacteriophages-always cause what is know as
lytic cycle which ends with the destruction of the
bacterial cell.For most phages the whole process from
attachment to lysis take less than 1 hour.
23. Latent Virus Infections
Herpes virus infections such as cold sores (fever
blisters) are good example of latent virus infections.A
fever,stress,or excessive sunlight can trigger the viral genes
to take over the cells and produce more viruses.
24. Antiviral Agents
It is important for healthcare professionals to understand the
antibiotics are not effective against viral infections.Antibiotics
function by inhibiting certain metabolic activities within cellular
pathogens and viruses are not cells.However for certain patients with
colds and Influenza,antibiotics maybe prescribed in an attempt to
prevent secondary bacterial infection that might follow the virus
infection.In recent years a few chemicals called antiviral agents have
been developed.
26. Human Immunodeficiency Virus is a
virus that attacks the bodys
immune system.If HIV is not treated it
can lead to AIDS(Acquired
Immunodeficiency Syndrome).Itis an
enveloped double staranded RNa
Virus.It is a member of a genus of
viruses called
Retroviridae(retroviruses).HIV is able
to attach to and in vade cells bearing
receptors that the virus recognize.
28. Plant viruses more than 1000
different of citrus trees,cocoa
trees,rice,barley,tobacco,turnips,ca
uliflower,potatoes,tomatoes,and
many other fruits,vegetables,trees
and grains.Plant viruses are usually
transmitted via insects such as leaf
hoppers,whiteflies,and round
worms.
