Transcript Viruses - Studyclix

Viruses
Contents
Definition
Shapes
Basic structure of a virus
Viruses are obligate
parasires
How viruses infect a cell
Viral Reproduction / Effect
of viruses on cell
Medical importance of
viruses
Economic importance of
viruses
Beneficial viruses
Conditions caused by
viruses
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Definition
virus: (plural = viruses) are non-cellular microorganisms, made up of a protein coat and one
type of nucleic acid (DNA or RNA) - obligate
parasites = can only multiply inside a living cell cause disease.
Are they living or non-living?
Examples of diseases caused by viruses are
influenza (flu), HIV (causes AIDS), chicken pox,
measles, mumps, rubella.
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Shapes
Viruses are found in a number of different shapes
e.g. bacteriophage, etc.
Note: names of various shapes not needed for L.C.
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Basic Structure of a Virus
Consists of a nucleic acid (DNA or RNA) and a
protein coat.
Some may have a membrane
coat outside of this, made from
the membrane of the cell that
was infected; with virus
proteins inserted into it e.g.
influenza.
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Viruses are obligate parasites
Can only replicate within other living cells.
Can only replicate within a limited no. of organisms.
Some only replicate within a specific type of cell of
the host.
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How viruses infect a cell
To infect a cell, the surface proteins of the virus
only bind with certain proteins on the surface of
the cell.
Viruses are specific.
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Viral Reproduction / Effect of Viruses
on Cells
(1/2)
When a virus enters a cell one of two things may
happen: 1. Viral DNA takes over the host cell – makes the
host cell produce copies of the viral protein and
DNA (or RNA) from materials within the cell.
These are then assembled into new viruses and
released by the bursting (lysing) of the host cell.
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Viral Reproduction / Effect of Viruses
on Cells
(2/2)
2.
Viral DNA may be inserted into the host DNA.
Becomes integrated with host DNA and is
passed on from generation to generation when
cell replication takes place.
These are lysogenic cells – and the new DNA
has no apparent effect.
Generations lateer – environmental conditions
may change (e.g. radiation, chemicals, etc.)
and activate the virus to make more copies of
itself and lysing the host cell.
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The possible effects of a virus on a cell
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Medical importance of viruses
They cause many diseases.
Antibodies cannot cure viral diseases.
Vaccinations available for some viral diseases e.g.
chickenpox, measles, etc.
No protection against other viral diseases e.g. AIDS.
Some new medicines interfere with viral replication
e.g. medication against cold sores.
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Economic importance of viruses
They damage crops e.g. tobacco mosaic virus.
Sick people effect the economy – out of work –
need to be cared for.
In parts of Africa 10% of the population is infected
with HIV – devastates their societies.
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Beneficial viruses
Very hard to find.
Bacteriophages used to destroy certain harmful
bacteria. Some kill disease-causing bacteria /
fungi e.g. Lambda bacteriophage attack E. coli.
Used in medical research e.g. in genetic
engineering and the production of DNA profiles
e.g. retroviruses produce the enzyme reverse
transcriptase which is needed for cutting the
DNA molecules in these processes.
Some viruses live in rhubarb and reduce size of
plant.
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Conditions caused by viruses
not examinable
for information only
Influenza
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Other conditions caused by viruses
Foot & mouth disease
Distemper
Myxomatosis
Rabies (hydrophobia)
Common cold
Measles
Mumps
Rubella = German measles
Smallpox
Chickenpox
Poliomyelitis = Polio
Viral pneumonia
Genital herpes
AIDS
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END
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