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Medicinal chemistry
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A virus is an infectious agent found in
virtually all life forms.
Viruses consist of genetic material, and
have a central core either DNA nor RNA
Although they are infectious agents,
they differ from bacteria in that they
contain no nucleus or cytoplasm.
They do not feed, excrete, or grow
They cannot reproduce outside of a
living cell.
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There are many types
of virus with varying
shape and structure.
All virus have a
central core of either
DNA or RNA
surrounded by a coat
of regularly packed
protein units called
capsid.
No nucleus or
cytoplasm like
bacteria.
Diagram of an AIDS Virus
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The replication of viruses can only occur if the
virus has attached and penetrated the living
host cell.
It injects it’s DNA or RNA into the host cell’s
cytoplasm.
It takes over the replication mechanism of the
host cell.
This causes the cell to die or to be altered,
which results in the symptoms of a viral
infection.
The host cell produces new viral DNA or RNA
cells which are then released to affect other
healthy cells.
A virus that contains RNA rather than DNA is
called a retrovirus.
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The virus uses the cell mechanism to replicate itself
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Viruses cause a number of illnesses and
diseases ranging from mild infections, such as
the common cold, to potentially fatal diseases,
such as acquired immunodeficiency syndrome
(AIDS).
It can be difficult to find effective methods of
preventing and treating viral infections for a number
of reasons:
1.
Once inside a host cell, a virus can multiply very
quickly and can have already spread throughout the
body by the time that symptoms have appeared.
2.
Viruses can mutate their DNA or RNA resulting in a
slight change in viral structure – this can make
them resistant to drugs and can prevent
vaccinations from being effective; this is particularly
true of viruses such as HIV.
3.
Viruses use the host cell’s own processes and
materials to produce new viruses, so it can be
difficult to design drugs that target only the virus
and do not affect the host cell.
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Several vaccines and antiviral drugs have
been developed and used to prevent and treat
viral infections successfully.
Vaccines stimulate the body’s natural
defences (the immune system) to produce
antibodies against a virus – so if infection
does occur, the immune system is prepared
and can stop the infection before it takes
hold. Vaccines have been used successfully
against a number of viruses including
measles, mumps and polio.
Alter the genetic material
 Some alter the genetic material within cells –
once inside a cell, the drug is converted into
an active metabolite that becomes
incorporated into the growing DNA strand
(needed for viral replication) halting its
synthesis. An example of a drug that acts in
this way is aciclovir(acyclovir), which is used
to treat cold sores; it stops viral DNA
replication and so stops the virus from
multiplying.
Inhibit the activity of enzymes
 Some inhibit the activity of enzymes within
the host cell that are necessary for the
formation of new viruses. An example is
indinavir, which is used in AIDS treatment; it
inhibits the HIV enzyme protease, which is
essential to the assembly of functional new
HIV viruses.
Preventing virus from binding host cells
 Some stop the viruses from infecting host
cells by preventing them from binding to the
host cell surface and gaining access into the
cell. Some drugs used to treat AIDS work in
this way
 Preventing virus from leaving host cell
 Some prevent the virus from leaving the host
cell so that it cannot infect other cells –
oseltamivir and zanamivir .
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Symptoms include fever, headache, aching
joints and fatigue.
In severe cases can even cause death
There are many cases of pandemics such as
“Spanish flue” in 1918 and swine flue in 2009.
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The influenza virus has RNA as its genetic material rather
than DNA.
The capsid contains RNA and RNA polymerase (an enzyme)
and surrounding this it has a lipid envelope which has two
very important proteins in it – neuraminidase (NA) and
hemagglutinin (HA). Both proteins stick out of the
membrane surrounding the virus.
Hemagglutinin allows viruses to bind to receptors on the
surface of cells to be infected
Neuraminidase help virus to infect cell by breaking down
its cell wall
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The virus enters the cell, replicates its RNA and
essential proteins, but then the new viruses have to
get out of the cell if they are to infect other cells.
They do this by budding
The virus will, however, remain bound to the surface
of the until the NA breaks the link between the sialic
acid and the rest of the membrane glycoprotein,
allowing the virus to break free from the cell.
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Oseltamivir/zanamivir may be taken when fl u
symptoms develop but they are also taken as a
prophylactic (a preventative measure) for people
who have been exposed to the virus or are in
high-risk groups (such as very young children).
Oseltamivir is administered orally as oseltamivir
phosphate but zanamivir has very poor
bioavailability when given orally and so is
formulated as a dry powder for oral inhalation.
Zanamivir is highly polar (see below) and cannot
pass across cell membranes.
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A 10-year study completed in
2005 found a strain of Simian
Immunodeficiency Virus (SIV)
in a number of chimpanzee
colonies in south-eastern
Cameroon that was a viral
ancestor of the HIV-1 that
causes AIDS in humans.
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In 1981 AIDS was first
identified within homosexual
men
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940,000 cases of AIDS were reported in
the United States from 1981 through
2004.
In 2004, about 39,000 new cases of HIV
infection were reported.
Currently, there are approximately 1.1
million people in the United States who
are infected with the human
immunodeficiency virus.
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Wide spread in Africa.
Lack of access to
education.
Reticence of some
leaders to recognize
the problem.
Lack of access to
treatment.
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AIDS ( Acquired
Immune
Deficiency
Syndrome) is
caused by a
retrovirus that
contains RNA
rather then DNA.
This specific virus
invades particular
cells, that are
within the immune
system making
the body unable to
fight off
infections.
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The human
immunodeficiency virus
(HIV), which causes
acquired
immunodeficiency
syndrome (AIDS),
principally attacks T-4
lymphocytes, a vital part of
the human immune system.
As a result, the ability of
the body to resist
opportunistic viral,
bacterial, fungal, protozoal,
and other infections is
greatly weakened.
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Scientists have identified three ways that
HIV infections spread:
1. Sexual intercourse with an infected person,
2. Contact with contaminated blood,
3. Transmission from an infected mother to her
child before or during birth or through
breastfeeding.
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While no medical treatment cures AIDS,
there are many drugs that have recently
been developed to eradicate the HIV virus.
Full blown symptoms of AIDS may not
appear for more then 10 years.
It usually takes 2-3 months after the initial
infection for a person to test positive for
HIV
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While no medical treatment cures AIDS,
there are many drugs that have recently
been developed to eradicate the HIV virus.
Although full blown symptoms of AIDS may
not appear for more then 10 years.
It usually takes 2-3 months after the initial
infection for a person to test positive for
HIV
During this time frame a person inflected
with HIV can easily spread the virus without
realizing it.
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