KEEPING HEALTHY - The bodies defence against infection
ways of fighting infectious diseases
drugs, antibiotics, monoclonal antibodies
Culturing microorganisms like bacteria - testing
Doc Brown's Biology Revision Notes
Suitable for GCSE/IGCSE/O level Biology/Science courses or equivalent
This page will answer many questions e.g.
How does our body defend itself when it
What are the physical and chemical methods of
What is a pathogen? What is our immune system? What is a vaccine?
How does vaccination-immunisation protect us?
How our bodies defend themselves against infectious diseases?
Be aware that our bodies
provide a good environment for many microbes to live and multiply at our expense
and can make us ill once they are inside our body.
need to be capable of stopping most microbes from getting in and dealing with any microbes which do get
Starting with a historic note
A simple example of how science
works - cleanliness reduces the incidence of infection!
Appreciate the contribution of Semmelweiss in controlling
the rate of patient infection to solving modern problems with the spread
of infection in hospitals.
Semmelweis worked in Vienna
General Hospital in the 1840s and witnessed large numbers of women dying
after childbirth from a puerperal fever disease.
He thought that the staff of the
hospital were spreading the disease via unwashed hands.
After instructing doctors and
nurses to wash their hands in an antiseptic solution, the mortality rate was
Although Semmelweis didn't
realise it at the time, the antiseptic solution was killing the infecting
Apparently, when he left the
Vienna hospital, the practice of washing hands in the antiseptic solution
was relaxed, and the death rates rose again!
With the advent of new strain of
bacteria today, there is now an even greater need for emphasis on hospital hygiene
than ever before - so, if on a hospital visit, PLEASE WASH YOUR HANDS in the
antiseptic gel provided.
What are the
Microorganisms that cause infectious disease are
Bacteria and viruses may reproduce rapidly inside
the body and may produce poisons (toxins) that
make us feel ill.
What is a bacteria?
Bacteria and certain protozoa are very
small cells which can rapidly reproduce by cell division in your body making you feel ill by
damaging your body's cells and producing toxins (poisons produced as a
by-product of the bacteria's cell chemistry).
What is a virus?
Viruses are NOT
cells and much smaller than bacteria, but damage the cells in which
they reproduce. Viruses replicate by invading a
cell and using the cell's genetic machinery to reproduce themselves ie
copies of the original virus. The virus 'invaded' cell then
bursts releasing lots of new viruses which go on to invade more healthy
cells. The cell damage makes you feel
ill as your body (temporarily) fights back to make as many good cells as it
can to replace those destroyed by the virus.
Fungi are also pathogens
and includes microorganisms like yeasts and moulds (so don't eat mouldy
How do our bodies
The body has different
physical and chemical ways of protecting itself
Physical mechanisms of protection from
Your skin and hairs and mucous
in the respiratory tract can stop a lot of the pathogen cells from entering
The whole of the respiratory tract from the nasal passage, down
the trachea and into the lungs is covered with mucous and lined cilia (fine
hairs that can move freely at their ends).
The hairs and mucous in your
dust and any other particles that might contain pathogens like
bacteria before they can get down into the lungs.
Cells in the trachea and bronchi
secrete mucous to trap pathogens.
The hair-like structure of
the cilia then move-push the mucous up to the back of the throat
where it can be swallowed,
and the cilia can
also move the
mucous along from the lungs up to the nasal passage -and then you can blow
The stomach produces
strong hydrochloric acid, a strong acid that kills most pathogens, and
a safe distance from the sensitive tissue of the mouth and
Skin in good condition acts as a
very effective physical barrier against pathogens.
As well as acting as a
physical barrier, your skin also secretes antimicrobial
molecules that can kill pathogens.
What happens if the skin is
When a cut in the skin occurs,
small sections of cells called platelets help the blood to clot quickly to
seal the wound (seal = scab when dry) and prevent microorganisms entering
the skin tissue or blood stream. Clotting also reduces blood loss.
The greater the concentration of platelets
in the blood the faster the clotting process ('sealing') can occur.
Chemical protection by
In tears our eyes produce a
chemical called lysozyme that kills bacterial microorganisms on the surface
of the eye.
Lysozyme is an enzyme that
breaks down the cell walls of bacteria, so destroying the
bacteria on the surface of the eye.
As already mentioned, your stomach contains quite
concentrated strong hydrochloric acid which kills the majority of pathogenic
bacteria - sadly not all of them at times!
The saliva produced in your mouth
contains molecules that can kill some of the pathogens that enter
Beyond the stomach
Not all the remaining pathogens
that reach the stomach from the mouth are killed by the hydrochloric
Some pathogens enter the
intestines and have to compete with the 'local' bacteria for food to
Your gut is full of bacteria -
the gut is their natural habitat.
These physical and chemical
defences are non-specific and can counteract a variety of types of
The IMMUNE SYSTEM
What is the immune system?
The immune system 'kicks in' if
pathogens do get inside your body.
The white blood cells are
present throughout your body in your blood system and therefore are always
at hand to defend you from invading pathogens and the do so in three main
ways - see sections (a) to (c) below.
If your white blood cell count
is low you are more susceptible to disease and infection, because this
equates to a weakening of your immune response system
For example, HIV/AIDS weakens
white cell action and hence the body has a weaker responding immune system
that allows pathogens to have a more devastating effect on the body -
sometimes with fatal consequences from a disease that in a healthy body
would not have proved fatal.
The immune system of the body produces specific
antibodies to kill a particular pathogen.
This leads to
immunity from that pathogen.
In some cases, dead
or inactivated pathogens stimulate antibody
If a large proportion of the population
is immune to a pathogen, the spread of the
pathogen is very much reduced.
More details on
the functions of the white blood cells of the immune system
What is the function of white
What is an antibody? What is an antigen? What is an antitoxin?
If pathogens like harmful
bacteria actually get into your body your
responds to destroy them to defend you from their harmful effects.
The most important feature of
your immune system is the function of the different types of
white blood cells.
These white blood cells are
travelling around the whole of your body in your bloodstream and
so are always available to tackle an infection.
More of the types of white
blood cells can be made to tackle any major infection, but
infections may take time to be cleared up completely.
When white blood cells meet
an invading pathogen (bacteria, virus etc.) they can respond in
three different ways.
(a) The ingesting
of pathogens by white blood cells - phagocytes
White cells can surround
'foreign' invasive microorganisms and break them up, effectively digesting
The white blood cells that do
this are called phagocytes and the process is called
Phagocytes are made and stored in
the bone marrow - the soft tissue at the centre of bones.
When an infection happens more
phagocytes are released and travel through the blood to the point
where the pathogen (e.g. bacteria) has entered the body and the
diagram shows what happens next.
phagocyte detects the presence o pathogens and moves towards
Phagocytes have a flexible membrane that changes shape and surrounds a clump of the pathogens.
The pathogens then become completely enclosed in the cytoplasm
of the phagocyte cell and can then be digested.
in the cytoplasm of the phagocyte break the pathogens down and
the products absorbed into the phagocyte's cytoplasm.
Producing antibodies, which destroy particular
bacteria or viruses.
All invading cells have unique
molecules ('molecular structure') on their surface called antigens.
When white cells encounter a
'foreign' antigen on a pathogen they don't recognise, they produce proteins
called antibodies which lock onto the antigens of the pathogen making
them more susceptible to phagocytosis - described above.
The white blood cells that
perform this task are called B-lymphocytes and the overall
process is described using the diagram below. These cells are
involved with specific immune responses.
1. Large numbers
of B-lymphocyte white blood cells (grey) are always present
in the blood and they can recognise OR not recognise, different
types of pathogens - bacteria and viruses.
All invading pathogens (green
O) have unique molecules on their surface called
-, often proteins). If the surface of the lymphocyte detects the
antigens (blue) on the surface of a 'foreign' pathogen they don't
recognise, a response is triggered by the lymphocyte cell.
The lymphocyte cell begins to produce protein molecules called
antibodies (black Y).
The antibodies move out of the cell to 'confront' the invading
pathogen and will not lock onto any other pathogen.
The antibodies lock onto the antigens on the surface of the
pathogen (e.g. invading bacteria cell).
6. The invasive
pathogen is then more easily found and destroyed by another type of
white blood cell - the phagocytes, which destroy them by
phagocytosis - described in section (a) above.
The antibodies often cause
the pathogens to clump together making it easier for the
phagocyte cells to find and ingest them by phagocytosis.
The white blood cells that
detect the pathogen then divide to produce more copies (clones)
of the same white blood cell, which in turn make more of the
The antibodies are produced
quite rapidly and move all around the body in the bloodstream to
find other similar pathogens.
Memory lymphocyte white
blood cells (memory cells) are also produced in the immune
response to a pathogen and the harmless forms you are vaccinated
They stay in the body for
a long time and 'remember' a specific antigen on the surface
membrane of a specific pathogen. This means if you get
re-infected, your body's response is much faster and more
effective - you might not even notice any symptoms!
The antibodies produced are
specific to that type of antigen, they will not lock onto any other type of
antigen, hence they are specific to a particular pathogen.
e.g. the antibody for the
measles virus is different to the antibody of chickenpox virus.
The production of antibodies by
the body in recognition of foreign material is called the immune
One the 'blueprint' antibody is
made, it is rapidly reproduced, carried round the body in the
bloodstream, and lock onto the specific invasive pathogens and
The immune response mechanism
of the white blood cells is the same in fighting either
bacterial or viral infections.
If a person becomes infected
with the same pathogen microorganism, the appropriate type of white blood cell will automatically,
and quickly, produce the correct specific antibodies to kill the pathogen because of the
first invasion of a particularly pathogen the person has become naturally immune
to the specific infection.
This is because once the
white blood cells have made an antibody in response to a
particular infection, they can easily recognise the specific
bacterium or virus and produce the same antibody again - see
below - more on memory lymphocytes.
This immunity helps prevent the immune person becoming ill again, or at
least minimises the chance of 2nd attack of the specific pathogen having any
More on memory lymphocytes
Memory lymphocytes are
naturally produced in the immune response to a pathogen.
When a pathogen enters your
body for the first time, the immune response is slow because
there are relatively few of the B-lymphocytes around capable of
making the antibody to combat a particular pathogen.
Eventually, your body will
produce enough of specific antibody to overcome the infection,
but in the mean time, you will display symptoms of the disease.
As well as antibodies, memory
lymphocytes are also produced by your immune response to a
foreign antigen of a pathogen. They stay around in the body for
some time and 'remember' a specific antigen on the surface
membrane of a specific pathogen.
The person is now got some
immunity to respond much more quickly to a second infection.
See also section on
If the same pathogen enters
your body again there are far more white blood cells around to
recognise the pathogen and produce antibodies to combat it.
In other words, the secondary
response is faster and stronger than the first immune response,
an, in many cases, destroys the pathogen before you exhibit any
Epidemics are large
scale outbreaks of an infectious communicable disease. Mass
vaccination programmes help reduce the chances of an epidemic,
but, a high percentage of a population needs to be vaccinated to
avoid the infection spreading rapidly.
(c) White blood cells
also help to defend against pathogens by:
Producing antitoxins, which counteract the toxins
released by the pathogens.
You can think of these
antitoxins as a sort of antibody that combines with the
poisonous waste product molecules produced by e.g. by bacteria
to form a harmless product - a sort of chemical 'neutralising'
effect (but NOT the acid-alkali variety!).
These antitoxins are very
specific chemicals that remove the toxicity effect of the toxins produced by
pathogen cell action.
How can our
health be further protected from pathogens? fighting infections!
Be able to explain how the treatment of disease has changed
as a result of increased understanding of the action
of antibiotics and immunity.
Be able to evaluate the consequences of mutations of bacteria
and viruses in relation to epidemics and pandemics
- data provided.
Be able to evaluate the advantages and disadvantages of
being vaccinated against a particular disease - data provided.
As already mentioned, Semmelweiss recognised the importance of
hand-washing in the prevention of
spreading some infectious diseases.
By insisting that doctors washed their hands
before examining patients, he greatly reduced the number of deaths from
infectious diseases in his hospital.
Some medicines, including painkillers, help to relieve
the symptoms of infectious disease, but do not kill
As we have seen, our immune system of the body produces specific
antibodies to kill a particular pathogen.
This leads to
immunity from that pathogen.
In some cases, dead
or inactivated pathogens stimulate antibody
If a large proportion of the population
is made immune to a pathogen by vaccination-immunisation, the spread of the
pathogen is very much reduced - which is what the next section is all about
If you become infected with a new
('foreign') pathogen that your immune system doesn't recognise as
'friendly', it takes your white blood cells a few days to produce the
antibodies to protect you.
In the mean time you are
unfortunately ill and not feeling well to a greater (fatal) or lesser
(a bit poorly) degree.
Vaccination is a
successful method to drastically reduce the response time of your
immune system and usually prevents the onset of the disease.
People can be immunised against a disease by
introducing small quantities of dead or inactive forms
of the pathogen into the body (vaccination).
The process of vaccination has
radically changed the way we fight disease because it is not about
treatment of a disease, it is all about preventing the effects of an
Know that vaccination is an
important method of
What is vaccination? What is a vaccine?
What is immunisation?
Vaccination protects the
individual from future infections and mass scale vaccination can greatly
reduce the incidence of disease.
Protection is better than cure!
If you become infected with a pathogen, it takes a few days for your white
cell immune system to deal with the microorganism, and you can become quite
ill in a few days.
Vaccination is the
process of injecting the individual with small amounts of specific harmless
dead/inactive microorganisms (pathogens) which carry the antigens that cause the immune
system to produce the corresponding protective antibodies - even though
the pathogen is in a harmless form.
The MMR vaccine
contains weakened versions of the viruses that cause measles,
mumps and rubella (German measles).
stimulate the white blood cells to produce antibodies
that destroy the invading 'foreign' pathogens.
This makes the person
immune to future infections by the microorganism ie gives the individual
immunity from further attacks - the overall process is referred to as
If the same type of pathogen,
that you have been vaccinated against, enters your body, your body can respond by
rapidly making the correct
antibody, in the same way as if the person had
previously had the disease.
Vaccination is when the
vaccine is administered to you (usually by syringe injection).
Immunisation is what
happens in your body after you have the vaccination.
The vaccine stimulates your
immune system so that it can recognise the disease (invasive
pathogen - bacteria or virus) and protect you from future
infection (i.e. you become immune to the infection).
The diagram and notes below what
happens on vaccination to complete the immunisation effect.
You are injected by vaccination with a weakened/inactive/dead form of the
pathogen - although harmless, your body will respond to the 'new'
antigens detected - an immune response.
Your lymphocyte white blood cells recognise the pathogen as harmful
and produce the antibodies to counteract 'what is perceived' as an
3. If the same
actually active pathogen enters your body, it is quickly recognised
by its antigen molecules and attacked by the specific antibodies
already present and more can be made too, quite rapidly.
4. The effect of
the pathogen is 'neutralised' so you don't become ill.
When the pathogens are combined with the antibodies they are much
more susceptible to be ingested by the phagocyte white blood cells
MMR vaccine is used to
triple protect children against
measles, mumps and rubella (German measles).
The vaccine contains weak
inactive versions of three viruses that cause measles, mumps and rubella.
The effects of vaccination can
'wear off' over time, and booster injections maybe necessary to increase the
levels of the protective antibodies.
There are arguments for and
against vaccination (the 'pros and cons').
resulted in the large scale control of many infectious diseases that were
once common and often fatal eg measles, mumps, polio, rubella, smallpox,
tetanus, whooping cough etc.
These communicable diseases
were once common in the UK but smallpox has been completely
eradicated and polio infections are very rare these days (down
as much as 99%)
Epidemics are less likely with mass vaccination
- spread of the disease is less likely as there are fewer infected people
carry an active form of the disease - but a large percentage of the
population needs to have been vaccinated - less people around to
carry and pass on the pathogen.
Without mass vaccination an outbreak of
epidemic proportions is much more likely - many more people potentially to carry
and transmit the disease which can spread rapidly, particularly
in densely populated areas where lots of people are in close
Some vaccines do
not always give you immunity but development work goes on all the time to
make more effective vaccines - especially as different strains of viruses
and bacteria are constantly evolving.
There may also be side-effects
in which the 'patient' has a bad reaction to a particular vaccine eg
swelling, fever, seizure (serious!), but such reactions and complications
are rare and the mass good effect of large scale immunisation should be balanced against the very rare negative
effect - however serious this might be.
There are some concerns over
using 'whole' pathogens so that the vaccine actually causes
disease in the person. Therefore some vaccines only use parts of
the pathogen cells which must include the antigens for the white
blood cells to react to.
Producing vaccines and
carrying out mass vaccination programmes can be expensive - the
disease may be rare or the vaccine proves to be not that
The benefits of vaccination
must outweigh the development and production costs involved.
There is a very small risk
involved with most medical treatments and although side-effects are not
uncommon, without vaccination some of these diseases are fatal or have very
serious non-fatal outcomes - people can die of from measles, rubella has
serious consequences for pregnant women, there can be serious complications
for infected people who have not been vaccinated.
Following a seaside accident -
cut on knee, as
an eleven year old, I collapsed unconscious after a tetanus injection at a
local hospital. I was ok within half an hour BUT my parents got a bit of a
Parents of young children are
always given details of vaccination schedules and where appropriate,
warned of side effects associated with specific vaccines.
Sadly in some countries,
including in the UK, a lot misinformation was put about on social
media about the supposed ill-effects of taking the MMR (mumps,
measles and rubella) vaccine e.g. causing autism. The information
was not backed up by real scientific data and as a result was
hundreds of thousands of young children were not vaccinated with
three medical conditions with potentially serious consequences.
More on fighting disease.
Keeping healthy - communicable diseases -
pathogen infections gcse
biology revision notes
Keeping healthy - non-communicable diseases
- risk factors for e.g. cancers gcse
biology revision notes
DRUGS - medicines to treat disease
Drugs are substances that affect
how the body works.
Most drugs are proven safe
medicines to use, but some are potentially dangerous if misused.
Many drugs can be bought directly
from a pharmacy, but others can only be obtained from a doctors
The first thing you should appreciate
is the difference between 'feeling better' and being 'cured'!
Some drugs like aspirin or
paracetamol relieve pain and reduce discomfort i.e. reduce the symptoms,
but they do not counteract the disease you are suffering from e.g. a
virus giving you a headache.
Such drugs do NOT cure you
because they do NOT kill the pathogen causing the disease in the
Lots of other drugs e.g. cold
remedies, decongestants, analgesic pain killers etc., cannot destroy
e.g. the cold or flue virus but do make you feel a lot better and
help you get a better nights sleep!
Other drugs e.g. the antibiotic
penicillin do kill or inhibit the growth of certain bacterial
(See next section on
However, they are not a 'blanket
cure', different types of bacteria require different types of antibiotic
and the correct match is required to effect a cure.
Culturing microorganisms like bacteria - testing
Unlike 'symptom relievers' like
aspirin, antibiotics like penicillin do kill or inhibit the growth of
certain bacterial infections.
However, they are not a 'blanket
cure', different types of bacteria require different types of
antibiotic and the correct match is required to effect a cure.
Never-the-less, the widespread
use of antibiotics has greatly reduced the number of deaths from
communicable diseases caused by bacteria.
Unfortunately, antibiotics do NOT
destroy viruses infections from e.g. flue or cold viral infections.
Virus attacks can be treated
with very specialised and expensive anti-viral drugs, but
since viruses reproduce in your own body cells, its difficult to
avoid damage to you own healthy body cells.
Antibiotics, including penicillin, are medicines that
help to cure bacterial disease by killing infectious
bacteria inside the body, without killing your own body cells.
What is an antibiotic? How do
NOTE: An antibiotic kills
bacteria in the body.
An antiseptic kills
bacteria outside the body e.g. on the skin or
disinfecting a worktop in the kitchen.
Antibiotics cannot be used
to kill viral pathogens, which live and reproduce inside
Antibiotics do NOT destroy
viruses, typified by the cold and flue viruses we all suffer from.
make your own body cells reproduce the invasive virus and unfortunately
anti-viral drugs may attack good cells too!
It is quite difficult, and
costly, to develop and market anti-viral drugs that will only
kill the virus and not your own body's healthy cells.
penicillin kill or prevent the growth of harmful pathogens, they kill the
bacteria but not your own healthy body cells.
Antibiotics work by
inhibiting processes in bacterial cells, they do NOT affect
the cells of the host organism.
Some antibiotics inhibit the
building of the cell walls of bacteria, which prevents cell
division - these antibiotics do not affect human cells which do
not have cell walls.
Different antibiotics attack
different bacteria, so it is important that specific bacterial infections
should be treated with the appropriate specific antibiotics.
The use of antibiotics
has greatly reduced deaths from infectious bacterial
However, overuse and inappropriate use of antibiotics
has increased the rate of development of antibiotic
resistant strains of bacteria.
You need to be aware that it is difficult to develop
drugs that kill viruses without also damaging the body’s
Explaining the use of antibiotics to
Antibiotics are taken internally e.g.
intravenous syringe injection, or orally taken by tablet or liquid suspension.
Antibacterials to treat bacterial infections
Probably the most well known antibacterial
is the antibiotic penicillin which is effective against many bacterial
infections BUT NOT viruses like the common cold or flue.
An antibiotics can kill bacteria or prevent
them growing and reproducing.
Many strains of bacteria, including MRSA, have
developed resistance to antibiotics due to mutations, which cause stronger more
resilient strains of bacteria to survive as a result of
To prevent further resistance
arising it is important to avoid over-use of antibiotics.
Knowledge of the development of resistance in bacteria
is limited to the fact that pathogens mutate, producing
Mutations of pathogens produce new strains.
Antibiotics and vaccinations may no longer be effective
against a new resistant strain of the pathogen.
strain will then spread rapidly because people are not
immune to it and there is no effective treatment.
Can bacteria become resistant
Unfortunately the answer is yes!
Bacteria will sometimes quite naturally mutate into forms that are resistant
to current antibiotics, so if you are infected with a new strain of bacteria,
your resistance from your 'current' antibiotic is not as effective.
If an infection is treated with
an antibiotic, any resistant bacteria from any mutations will survive and this means
more resistant bacteria
can survive and reproduce to infect other people, while the non-resistant
strains will tend to be reduced.
This bacterial mutation is an example of
selection at the individual cell level and drug companies are constantly
trying to develop new antibiotics to combat the new evolving strains of
harmful bacteria - but new harmful 'superbugs' are becoming more common the
more we use antibiotics and new epidemics can break out!
staphylococcus aureus causes serious wound infections (including after
surgery in a hospital), can't be treated with many current antibiotics and
causes serious wound infections that can be fatal to young babies or elderly
people in particular.
Misuse by over-prescribing antibiotics is
believed to be causing the rise of mutant resistant strains of bacteria, so
doctors are being advised to avoid over-prescribing antibiotics to reduce
the mutation rate and not treating mild infections with antibiotics.
Symptoms like headaches
or sore throats are not a justification for being prescribed
antibiotics. Unfortunately, many patients (for various
reasons) are prescribed antibiotics when they are actually
suffering from a viral infection.
BUT, if an antibiotic is
appropriately prescribed, you should always complete the
course, even if you feel a lot better, this is to
maximise killing the bacterial infection and minimise
the chance of passing on of the infection.
It isn't just bacteria that can
mutate, viruses can also evolve via new mutations. Viruses are
notable for the rapidity with which they can mutate which makes it difficult
to develop new vaccines. The reason being that changes in the virus (or
bacteria) DNA leads to different gene expression in the form of different
antigens, so different antibodies are needed. The flue virus is a never
ending problem and in the past pandemics (epidemics across many countries at
the same time) have killed millions of people, mercifully this rarely
happens these days thanks to antibiotics.
Understand that antibiotics kill individual pathogens of the
Individual resistant pathogens survive and
reproduce, so the population of the resistant
Now, antibiotics are not used to treat
non-serious infections, such as mild throat
infections, so that the rate of development of
resistant strains is slowed down.
The development of antibiotic-resistant strains of
bacteria necessitates the development of new antibiotics.
Culturing microorganisms like bacteria - testing antiseptics gcse
Antibiotics kill pathogens in your
body, antiseptics kill pathogens outside of your body e.g. on the
surface of your skin or disinfecting surfaces in the kitchen.
Antiseptics are used to clean wounds
by killing microorganisms or stopping them multiplying.
The use of antiseptics in hospitals
and GP surgeries is vital to prevent the spread of infectious diseases
You should always
cleanse-disinfect your hands with the facilities provided before
visiting someone in hospital.
There are many commercial antiseptic
cleaning substances available for your kitchen, toilets etc.
Most claim to 'kill 99% of all
Antivirals are drugs used to treat
Most antivirals do not kill the virus
but stop them reproducing.
They are not easy to develop as
effective anti-virus agents because it is difficult to target the virus
without damaging the host cells.
TESTING NEW DRUGS
Products of the
Chemical & Pharmaceutical Industries & impact on us
(GCSE chemistry notes)
It has been known for some time that
plants produce a wide range of chemicals to defend themselves against
attack from e.g. insect pests or pathogen microorganisms.
Historically, currently and in the
future, these substances provide a basis for developing drugs to treat
Even some of our current medications
come from knowledge of plants giving us many traditional
herbal recipes e.g.
(i) The painkiller aspirin
was developed from chemicals in willow plants that reduce fever and
reduce pain in childbirth.
(ii) Drugs like digitalis
have developed from chemicals found in foxglove plants and are used
to treat heart conditions.
Many antibiotics are made from
growing microorganisms (first found by 'accident'!) e.g.
(i) The famous scientist
Alexander Fleming noticed in some petri dishes used for
investigating bacteria, a mould had grown, but the area
around the mould was free of bacteria.
He realised that the mould
(in this case Penicillium notatum), was producing a chemical
that killed the bacteria.
This chemical was extracted
and named penicillin, and proved to be a very effective
antibiotic in killing various bacterial infections.
(ii) These days pharmaceutical
companies grow fungi and other microbes on a large scale and extract
the antibiotic molecules in the laboratory.
These days drugs are manufactured
on a huge scale in the pharmaceutical industry.
Chemists can synthesis molecules
based on naturally found organic compounds from plants and also lots
of molecules that have never existed in nature until synthesised in
a modern chemical laboratory.
Historically, most effective
drugs were discovered by accident e.g. somebody by chance notices
some effect of a chemical which might have a medical
However, these days, research
is very systematic and we have an extensive database of
knowledge about the structure and properties of molecules AND how
Some drugs have been successfully
designed by computer software that can construct and display
molecular structure e.g. design a molecule with a shape to fit into
the active site of an enzyme to inhibit its action.
Products of the
Chemical & Pharmaceutical Industries & impact on us
(GCSE chemistry notes)
Developing a new drug - a lengthy and
The drugs developed and produced by
the pharmaceutical industry are often very costly in the making for
You have to carry out a lot of
research and development to find a suitable compound that performs an
effective medical treatment for some condition e.g. to reduce blood
pressure, kills cancer cells, slows down the development of dementia etc.
The compound must be tested, often
modified and retested.
All new potentially useful drugs must be fully
tested in trials including animal trials (controversial) and human
trials and this all takes time and money.
Until a drug has fully
passed all safety and effectiveness tests it cannot be marketed and sold
to medical institutions from hospitals to high street pharmacies etc. The
manufacturer must prove that any pharmaceutical product like a drug does
meet all legal requirements that it does actually work and is safe to
The stages in the testing of a new
drug-medicine is summarised below:
Stage 1 Preclinical testing
(non-living animal testing):
Computer models can be used
initially to simulate a human's responses to a drug and can
identify possible effective drugs, but cannot possibly be as
accurate as actually using cell tissue cultures or live animals.
In preclinical testing the
drugs are tested on human tissue cells in the laboratory.
However, these procedures
cannot be used to test drugs that affect a complex body system.
e.g. a drug for controlling blood pressure must be tested on the
whole live animal with its complete circulatory system.
Stage 2 Preclinical testing
(live animal testing):
If the stage 1 tests prove
satisfactory, and no potential harmful effects are detected, you
can then move onto testing the drug on live animals.
This is to see whether the
drug works and producing the desired medical effect (this is
known as testing the efficacy of the drug).
You are also looking for
potential harmful effects, including toxicity.
You are also investigating
the appropriate dosage in terms of concentration/amount and
frequency of administering the drug.
According to UK law, any new
drug must be tested on two different live mammals, but there are
objections to this on several grounds:
(i) Many people object on
the grounds it is cruel and unethical to use animals in
tests, but others think drug safety should override these
considerations i.e. avoid the use of a potentially dangerous
(ii) Animals used in
testing drugs are not quite the same as humans. Could their
biological differences give us false results in terms of the
efficacy of the drug when used on humans?
Stage 3 Clinical testing on
If the drug has passed all
the preclinical tests, you can then test it on human
volunteers in what is called a clinical trial - which
is just as complicated as any research laboratory testing.
Initially, the drug is
tested on healthy volunteers - this is the only way to
find out if there are any harmful side effects on a
healthy body working normally. Initially it is unsuitable to
test the drug on sick people who are likely to be more
vulnerable to side effects.
At first very low doses of
the drug are administered to healthy people and then the dose is gradually
If the results of the tests
on healthy individuals are good and meet any health and safety
criteria, the drug can then be tested on patients suffering
from the illness-disease the drug is designed to combat.
From these tests the
optimum dose is found - that is the dose that is most
effective with the fewest side effects.
The safety and
effectiveness of the new drug must be thoroughly
This takes some time,
human drug trials may last for months or even years.
Sometimes this is due
to the long term progression of a disease e.g. cancer
and the time taken for the treatment to be shown to be
It might also be a
long time before the symptoms of side effects show up.
We now get into the practice
of how to get statistically valid results from real
To test the effectiveness of
a drug a group of patients are randomly selected into two
One group is given the
new drug and the other group a placebo - a
substance that is like the drug being tested, but has no
effect - it can be just a sugar pill.
Using a placebo ensures
the doctors can see the real difference the drug is having
on the patient's condition. This also allows for
where the patient does expect an improvement in their
medical condition and might actually feel better - even though unknowingly, nothing is
suppose to improve!
In some trials on
seriously ill patients, placebos are not used -
it would be unethical not to allow all patients the same
chance of benefiting from the new drug.
In other trials
doctors might test new drugs against the best existing
treatment instead of testing against a placebo.
Note that that
clinical trials must be blind, meaning, the patient in
the trial doesn't know whether they are getting the new drug
or a placebo.
Sometimes the clinical
trials are double-blind where neither the patients
nor the doctors know who has the drug or placebo until all
the results have been gathered and analysed. This ensures
the doctors administering, monitoring and analysing the drug
trial are not subconsciously influenced by their knowledge
of the patients.
Before any drug is approved
for use in our healthcare systems, the results of drug testing
trials must be peer reviewed by other equally qualified
This is essential to
avoid false or biased claims of the new drug's performance
in real patients.
Peer reviewers check the
validity of the drug trial e.g. has it been correctly
designed and rigorously carried out to the highest
Finally, the drug can
only be approved for patients of the general public
after permission is granted by the appropriate
medical agency if all health and safety criteria are
met. The rules are strict to ensure the drugs are as
effective and safe to use as possible.
ANTIBODIES - production and uses
You need to have read about
antibodies before studying this section.
How do you make monoclonal antibodies?
As we have seen, antibodies are produced by the type of white
blood cell called B-lymphocytes. It is proving useful to medicine to
produce lots of a specific antibody from multiple clones of a single
white blood cell. The antibodies will be identical and only target one
specific antigen protein molecule. Unfortunately, lymphocyte cells
do not divide easily, but tumour cells can be readily cultured to
undergo rapid cell division.
The process starts by (i) injecting a mouse with a specific
antigen and then extracting the B-lymphocytes produced and (ii)
culturing tumour cells.
(iii) You then fuse a mouse B-lymphocyte with a tumour cell to create a
'hybrid' cell called a hybridoma cell - which can be cloned
to make lots of identical cells. It is these cells that produce
identical monoclonal antibodies, which can be collected and
purified for research or direct medical use.
If possible, you can produce monoclonal antibodies that bind to
anything you want e.g. an antigen that is only found on the surface
of a one specific type of cell e.g. a target cancer cell.
Because monoclonal antibodies only bind to a specific antigen
molecule, you can therefore target a specific cell and destroy it
(e.g. a cancer cell) or 'neutralise' a chemical in the body to
inhibit its poisonous action.
Uses of monoclonal antibodies
1. Treating diseases using monoclonal antibody techniques
As we have seen, different cells in the body
have different antigen molecules on their surface, which
gives them a unique molecular signature.
This means you can make monoclonal antibodies
that will bind to ('target') specific cells with that specific
Cancer cells have antigens on their cell
membranes that you do not find on normal healthy body cells and they
are known as tumour markers.
In the laboratory you can culture cells to
produce monoclonal antibodies (see above) that will bind to these
tumour marker antigens, but the real trick is other things you can
do with the monoclonal antibody e.g.
anticancer drug-agent can be attached to the monoclonal antibody
- see the diagram below.
The anti-cancer agent might be a toxic drug or
radioactive substance (radioisotope) or chemical that inhibits the
growth and division of cancer cells. Any toxic effect will only
kill the cancer cells, not the healthy non-cancerous cells,
because the anti-cancer agent is only attached to the cancer cell
antibody, which itself, will only attach itself to the cancer
cells - that's the way the antigen-antibody mechanism works.
Advantages and problems with using monoclonal antibodies
Despite the wonderful advantages of
applying monoclonal antibodies to medical treatments, there are
the 'usual' pros and cons.
In other cancer treatments e.g.
chemotherapy and radiotherapy you inadvertently damage
neighbouring healthy cells as well as killing the cancer cells
because of the high energy of the radiation (often gamma
radiation). This doesn't happen with monoclonal antibody drug
cancer treatment where the side effects are much less.
Unfortunately, monoclonal antibodies do
cause more side effects than expected.
Symptoms exhibited include fever, low
blood pressure and vomiting.
These side effects have limited the
use of monoclonal antibody drug treatments.
2. Tests for tracing and measuring specific substances
to help in medical diagnosis
e.g. monoclonal antibody applications include
(a) Binding them to a specific hormone
or other molecule in the blood to measure the
concentration ('level' of chemical).
(b) Testing blood samples for the
presence of specific pathogens.
(c) Tracing and locating specific
molecules on cell or tissue.
You first make monoclonal antibodies
that bind to the specific molecule X you are
The antibodies are then reacted to
bind with a fluorescent dye molecule to facilitate an
If the molecule X is present in
your analysis sample, the monoclonal antibody will attach
itself to it.
Therefore the presence, location and
concentration of molecule X can be obtained using uv
light to cause a fluorescent effect.
(d) Testing for cancer.
You first make the specific antibody
that will bind to the cancer cells, but this antibody is
labelled with a radioisotope.
The radioactive labelled antibody
is fed into the patient through a drip into the bloodstream
and carried all the way around the body.
When the antibody encounters a cancer
cell it will bind to it because it recognises the antigen of
the cancer cell (the tumour marker).
The radiation emitted from the
radioactive tracer is monitored by a special camera (linked
to a computer and screen) and where the cancer cells are
concentrated, the emitted radiation will be the greatest -
this will show up as a bright 'hot spot' on the
Therefore doctors can see exactly
where the cancer is, the size of the tumour and, from
previous scans, whether the cancer is spreading e.g.
secondary cancers from prostate cancer i.e. cancer spreading
out of the prostate gland.
using monoclonal antibodies to treat cancer in
(e) Using monoclonal antibodies to find
Blood clots form when proteins in the
blood join together to form a solid mesh that restricts
You can make monoclonal antibodies,
labelled with a radioactive tracer, that bind to these
After injection of these monoclonal
antibodies into the bloodstream, a special camera (linked to
a computer and screen) can pick out where the blood clot is
where there is a high concentration of the radioisotope -
shown by a bright 'hot spot' on the screen.
Blood clots are very potentially
dangerous and this technique is able to detect them and
allow the doctor to remove them before the patient comes to
3. Pregnancy testing using monoclonal antibodies
Monoclonal antibodies are used in a pregnancy
test strip/stick which can detect the HCG hormone which is present
in the urine of pregnant women. The science behind the test is
illustrated in the diagram below.
You wee onto the end of the strip or dip it into a collected sample
of urine - the method is upto you!
The reaction zone is impregnated with the HCG antibody which has
been modified with an enzyme (e) to facilitate a colour
effect if HCG hormone is present.
As the urine diffuses up the strip this
1st antibody combines with any HCG hormone in the urine and
continues moving along the strip.
In the test zone the HCG combination encounters and attaches itself
to a 2nd, but immobile antibody.
If the HCG hormone is present in the urine
the enzyme triggers a chemical reaction to give a colour change
e.g. the appearance of blue colour would signify a positive
If the HCG hormone is not present, no
colour change is seen, indicating a negative pregnancy result
The control zone is to check that the strip is working correctly,
irrespective of a positive result.
As the urine diffuses further up the strip
it carries along some of the first HCG antibody (with enzyme
e) that has not combined with the HCG hormone. It then
encounters an immobile version of the 2nd antibody which already
has the HCG hormone attached to it
If the pregnancy stick is behaving
correctly, you should get the same colour change as if it was a
positive pregnancy test.
Note: You can impregnate the strip with
different antibodies to test for the presence of other substances in
the urine e.g. the antigens on other pathogens.
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