HeeJae Lim
Chandni Agrawal
Catherine Pua
Distinguish between antigens and antibodies.
From the powerpoint
By Stephen Taylor
Antigen causes the disease, and antibody acts against the disease!
Antigen:

An antigen is a large molecule (protein, glycoprotein, lipoprotein or polysaccharide) on
the outer surface of a cell.

All living cells have these antigens as part of their cell membrane or cell wall.

The capsid proteins of viruses and even individual protein molecules can also be
classed as antigens.

Their purpose is for cell communication, and cells from different individuals have
different antigens, while all the cells of the same individual have the same antigens.

Antigens are genetically controlled, so close relative have more similar antigens than
unrelated individuals.

Blood groups are an example of antigens on red blood cells, but all cells have them.
The link with infection is that when a pathogen or toxin enters the body it this that the
immune system reacts against.
HeeJae Lim
Chandni Agrawal
Catherine Pua
Antibodies are proteins secreted from lymphocytes that destroy pathogen and antigen
infections

B-cells make antibodies.

An antibody (also called an immunoglobulin) is a protein molecule that can bind
specifically to an antigen.

Antibodies all have a similar structure composed of 4 polypeptide chains (2 heavy
chains and 2 light chains) joined together by strong disulphide bonds to form a Yshaped structure.

The stem of the Y is called the constant region because in all immunoglobulin's it has
the same amino acid sequence, and therefore same structure.

The ends of the arms of the Y are called the variable regions of the molecule because
different immunoglobulin molecules have different amino acid structure and therefore
different structures.

These variable regions are where the antigens bind to form a highly specific antigenantibody complex, much like an enzyme-substrate complex.

Each B-cell has around 10 5 membrane-bound antibody molecules on its surface and
can also secrete soluble antibodies into its surroundings.

Every human has around 108 different types of B cell, each making antibodies with
slightly different variable regions.

Between them, these antibodies can therefore bind specifically to 108 different
antigens, so there will be an antibody to match almost every conceivable antigen that
might enter the body.
From Click4Biology
HeeJae Lim
Chandni Agrawal
Catherine Pua
Explain why antibiotics are effective against bacteria but not against viruses.
Antibiotics are medicines that help your body fight bacteria and viruses, either by directly
killing the offending bugs or by weakening them so that your own immune system can fight
and kill them more easily. The vast majority of antibiotics are bacteria fighters; although
there are millions of viruses, we only have antibiotics for half-a-dozen or so of them.
Bacteria, on the other hand, are more complex (while viruses must "live" in a "host" (us),
bacteria can live independently) and so are easier to kill.
Virus
Bacteria
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But bacteria can become resistant to antibiotics. Bacterial genes mutate (change), just like the
genes of larger organisms (including humans) mutate. Some of these changes happen because
of chemical or radiation exposure; some just happen randomly, and no one's sure quite why.
If bacteria with a changed gene is less susceptible to an antibiotic, and that antibiotic is
around, the less susceptible (and more resistant) version of the bacteria is more likely to
survive the antibiotic and continue to multiply.
Since antibiotics interrupt the basic biological functions of bacteria it is easier for them to
detect and fight against bacteria but because viruses are non-living things, it is hard for
antibiotics to fight against them. There is only half a dozen antibiotics to fight the millions
and millions of viruses which also have fault in them. Human and animal viruses can develop
resistance to antiviral antibiotics, usually through mutation. This isn't a big issue, since there
aren't a lot of antiviral antibiotics. However, antiviral resistance has become a major problem
in diseases such as HIV (AIDS) therapy, where the virus rapidly becomes resistant to the
first-line antivirals such as AZT.
Outline the principle of challenge and response, clonal selection and memory cells as the
basis of immunity.

Challenge and Response
An immune system must be challenged to by invading pathogens to respond by
antibody production from the lymphocytes.

HeeJae Lim
Chandni Agrawal
Catherine Pua
When the lymphocyte responds, it clones itself to produce a large number of
antibodies to fight the pathogen.
Colonal Selection:
 A pathogen is engulfed by a phagocyte, macrophage, and antigens from the engulfed
pathogen are displayed on the surface.
 They are bound to MHC protein, a membrane protein.
 Antigens are characteristic to the type of cell, hence only the antibody that has the
complementary shape can attach to the antigen marker.
 A receptor on a specific T-lymphocyte cell will bind to the antigens and be activated.
 The T-cell will then bind to a specific B-cell and stimulate the B-cell to divide,
forming clones of plasma B-cells or memory B-cells.
 The plasma B-cells secrete antibodies specific to the invading pathogen.
 The T-cell may also activate the killer T-cells that puncture the cell membrane of the
invader, destroying the cell.
 With viruses, the killer T-cell destroys the infected cell body preventing the virus
from reproducing.
 After the foreign pathogens have been defeated, suppressor T-cells signal the immune
system to shut down, stopping the production of antibodies.
Memory Cells
 The cloned memory b-cells will remain in the body long after the invasion by the
pathogens to prepare for future invasions.
 When the same pathogen infects the body, the memory b-cells will help produce a
quicker response against the infection.
HeeJae Lim
Chandni Agrawal
Catherine Pua
HeeJae Lim
Chandni Agrawal
Catherine Pua
Bibliography
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