INTRODUCTION
Viruses
are small obligate intracellular parasites which by definition
contain either a
RNA a or DNA genome, surrounded by a protective virus –
coded protein coat.Edward
Jenner (1798) introduced the term virus in
microbiology. Virus
Greek means ‘’ poison’’. In
1892 for the first time a
Russian botanist DMITRI IWANOWSKI discover the virus. They are infectious and cause various diseases to host organism. They come in different shapes. Based on the types of host cells or organisms, there are different types of viruses as
plant viruses,
animal viruses,
bacteriophages,
fungal viruses,
protists viruses, etc.
However, this article mainly focuses on the difference between plant virus and animal virus.
plant viruses,
animal viruses,
bacteriophages,
fungal viruses,
protists viruses, etc.
However, this article mainly focuses on the difference between plant virus and animal virus.
SHAPE
Viruses are of different shapes such as
spherical or cuboid ( adenovirus),
spherical or cuboid ( adenovirus),
elongated
(potato viruses),
flexuous or coiled (beet yellow),
bullet-shaped (rabies virus),
flexuous or coiled (beet yellow),
bullet-shaped (rabies virus),
filamentous ( bacteriophages M13),
pleomorphic.
pleomorphic.
SIZE
Variable size
from 20 nm to 300 nm in diameter. They
are smallest than bacteria,
some are slightly larger than protein and nucleic
acid molecules and some are
about of the same size ( smallpox virus) as the
smallest bacterium and some
virus slightly large (300 – 400 nm).
HELICAL
( CYLINDRICAL) VIRUSES
The
helical viruses are elongated, rod-shaped, rigid or flexible. There the capsid is a hollow cylinder with a helical structure. Capsid
consists of monomers arranged helically in the rotational axis. The
consist may be naked e.g. TMV or envelope e.g. influenza virus.
POLYHEDRAL (ICOSAHEDRAL) VIRUSES
Polyhedral the structure has the three possible symmetries such as
tetrahedral, octahedral and
icosahedral.
The
viruses are more or less spherical, therefore icosahedral symmetry is
the best
one for packaging and bonding of subunits. The
cap Somers of each
face form an equatorial triangle and 12 intercepting point
or corners.
They
consist of naked capsid e.g. adenovirus or envelope e.g. herpes simplex virus.
COMPLEX
VIRUSES
The
viruses which have the unidentifiable capsids or have the capsids with
additional structures are called complex viruses. Capsids
not clearly identified
e.g. vaccinia virus etc. Capsids to which some other the structure is attached
e.g. some bacteriophages etc.
ENVELOPE
There are certain plant and animal viruses and bacteriophage both
There are certain plant and animal viruses and bacteriophage both
icosahedral and helical, which are surrounded by a thin membranous envelope.
This envelope is about 10-15 µm thick.
it is made up of protein, lipids and
carbohydrates. Which are combined to form
glycoprotein and lipoprotein? Lipids provide flexibility to the shape, therefore viruses look of variable
size and shape. The protein component of the envelope is of viral origin and
lipid and carbohydrate may be the feature of the host membrane.
The key difference between plant virus and the animal virus is that the plant virus is an intracellular parasite that infects plants while the animal virus is an intracellular parasite that infects animal tissues.
Plant Viruses
Plant viruses, like other viruses, contain a core of either
DNA or RNA. You have already learned about one of these,
The tobacco mosaic virus.
As plants have a cell wall to protect their cells, these viruses do not use receptor-mediated endocytosis to enter host cells as is seen with animal viruses. For many plant viruses to be transferred from plant to plant, damage to some of the plants’ cells must occur to allow the virus to enter a new host.
As plants have a cell wall to protect their cells, these viruses do not use receptor-mediated endocytosis to enter host cells as is seen with animal viruses. For many plant viruses to be transferred from plant to plant, damage to some of the plants’ cells must occur to allow the virus to enter a new host.
This damage is often caused by weather, insects, animals,
fire, or human activities like farming or landscaping. Additionally,
plant offspring may inherit viral diseases from parent plants.
Plant viruses can be transmitted by a variety of vectors,
through contact with an infected plant’s sap, by living organisms such as insects and nematodes, and through pollen.
When plants viruses are transferred between different plants,
this is known as horizontal transmission, and when they are
inherited from a parent, this is called vertical transmission.
Symptoms of viral diseases vary according to the virus and its host (see the table below). One common symptom is hyperplasia, the abnormal proliferation of cells that causes the appearance of plant tumours known as galls.
Other viruses induce hypoplasia, or decreased cell growth,
in the leaves of plants, causing thin, yellow areas to appear.
Still, other viruses affect the plant by directly killing plant cells,
a process is known as cell necrosis. Other symptoms of plant viruses
include malformed leaves, black streaks on the stems of the plants,
altered growth of stems, leaves, or fruits, and ring spots, which are
circular or linear areas of discolouration found in a leaf.
Plant viruses can seriously disrupt crop growth and development, significantly affecting our food supply. They are responsible for poor crop quality and quantity globally and can bring about huge economic losses annually. Others viruses may damage plants used in landscaping. Some viruses that infect agricultural food plants include the name of the plant they infect, such as tomato spotted wilt virus, bean common mosaic virus, and cucumber mosaic virus. In plants used for landscaping, two of the most common viruses are peony ring spot and rose mosaic virus. There are far too many plant viruses to discuss each in detail, but symptoms of bean common mosaic virus result in lowered bean production and stunted, unproductive plants. In the ornamental rose, the rose mosaic disease causes wavy yellow lines and coloured splotches on the leaves of the plant.
Animal Viruses
Animal viruses, unlike the viruses of plants and bacteria, do not
have to penetrate a cell wall to gain access to the host cell.
Non-enveloped or “naked” animal viruses may enter cells in two different ways. As a protein in the viral capsid binds to its receptor
on the host cell, the virus may be taken inside the cell via a
vesicle during the normal cell process of receptor-mediated
endocytosis. An alternative method of cell penetration used by non-enveloped viruses is for capsid proteins to undergo shape changes after binding to the receptor, creating channels in the host cell membrane. The viral genome is then “injected” into the host cell through these channels in a manner analogous to that used by many bacteriophages. Enveloped viruses also
have two ways of entering cells after binding to their receptors:
receptor-mediated endocytosis, or fusion. Many enveloped viruses enter the cell by receptor-mediated endocytosis in a
fashion similar to some non-enveloped viruses. On the other hand,
fusion only occurs with enveloped virions. These viruses, which include HIV among others, use special fusion proteins in their envelopes to cause the envelope to fuse with the plasma membrane of the cell, thus releasing the genome and capsid of the virus into the cell cytoplasm.
After
making their proteins and copying their genomes, animal viruses complete the
assembly of new viruses and exit the cell. As we have already discussed using
the example of HIV, enveloped animal viruses may bud from the cell the membrane
as they assemble themselves, taking a piece of
the
cell’s plasma membrane in the process. On the other hand, non-enveloped viral
progeny, such as rhinoviruses, accumulate in infected cells until there is a
signal for lysis or apoptosis and all viruses are released together. Animal
viruses are associated with a variety of human diseases.
Some of them follow the classic pattern of
acute disease, where symptoms get increasingly worse for a short period followed
by the elimination of the virus from the body by the immune system and eventual recovery from the infection.
Examples of acute viral
diseases
are the common cold and influenza. Other viruses cause long-term chronic
infections, such as the virus causing hepatitis C, whereas others, like herpes
simplex virus, only cause intermittent
symptoms. Still other viruses, such as human
herpesviruses 6 and 7, which in some cases can cause minor childhood disease
roseola, often successfully cause productive infections without causing any
symptoms
at all in the host, and thus we say these patients have an asymptomatic
infection.
In
hepatitis C infections, the virus grows and reproduces in liver cells, causing
low levels of liver damage.
The
damage is so low that infected individuals are often unaware that they are
infected, and many infections are detected only
by
routine blood work on patients with risk factors such as intravenous drug use. On the other hand, since
many of the symptoms
of viral diseases are caused by immune responses,
a lack of symptoms is an indication of a weak
immune response to the
virus. This allows the virus to escape elimination by the immune system and persist in individuals
for years, all the while producing low levels of progeny virions
in what is known
as a
chronic viral disease. Chronic infection of the liver by this
the
virus leads to a much greater chance of developing liver cancer,
sometimes
as much as 30 years after the initial infection.
As
already discussed, the herpes simplex virus can remain in a state of latency in
nervous tissue for months, even years.
As the
virus “hides” in the tissue and makes few if any viral proteins, there is
nothing for the immune response to act against, and immunity to the virus
slowly declines.
Under
certain conditions, including various types of physical and psychological
stress, the latent herpes simplex virus may be reactivated and undergo a lytic
replication cycle in the skin, causing the lesions associated with the disease.
Once
virions are produced in the skin and viral proteins are synthesized, the immune
response is again stimulated and resolves the skin lesions in a few days by
destroying viruses in the skin. As a result of this type of replicative cycle,
appearances of cold sores and genital herpes outbreaks only occur
intermittently,
even
though the viruses remain in the nervous tissue for life. Latent infections are
common with other herpesviruses as well, including the varicella-zoster virus
that causes chickenpox. Some animal-infecting viruses, including the hepatitis C
virus discussed above, are known as oncogenic viruses: They have the ability to
cause cancer. These viruses interfere with the normal regulation of the host
cell cycle either by
either
introducing genes that stimulate unregulated cell growth (oncogenes) or by
interfering with the expression of genes that inhibit cell growth. Oncogenic
viruses can be either DNA or RNA viruses.
Cancers
known to be associated with viral infections include cervical cancer caused by
human papillomavirus (HPV), liver cancer caused by hepatitis B virus, T-cell leukemia,
and several types of lymphoma. HPV, or human papillomavirus, has a naked
icosahedral capsid
visible
in this transmission electron micrograph and a double-stranded DNA genome that is
incorporated into the host DNA. The virus, which is sexually transmitted, is
oncogenic and can lead to cervical cancer.
What
are the Similarities Between Plant Virus and Animal Virus? Both plant virus and
animal virus are intracellular obligate parasites. They live within a host
cell. Moreover, they have either DNA or RNA genomes.Both types of viruses cause
various diseases.
Furthermore,
their genomes can either be single-stranded or double-stranded.
Also,
both can either be naked or enveloped.
What
is the Difference Between Plant Virus and Animal Virus?
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