Download Antigens and Antibodies

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Lab:
Immunity - Antigens and Antibodies
The human body is well protected against invading pathogens. The first line of
defense prevents harmful microorganisms from getting into the body by
blocking their entry. The skin, when unbroken, provides an effective physical
barrier to nearly all pathogenic organisms. Secretions such as tears, saliva, and
mucus provide an effective physical and chemical barrier; they contain enzymes
that destroy pathogens or help trap and flush them out of the body. Nevertheless,
some pathogens manage to elude the first line of defense and gain entry. They
may do so through breaks in the skin (cuts and scrapes) or through the eyes and
natural openings in the body, such as the mouth and nostrils. Some pathogens
produce toxins, or poisonous wastes. Once inside, these invaders are
confronted by the immune system, the body's primary defense mechanism.
Invaders may be destroyed by being engulfed by special cells or by being
chemically marked for destruction and elimination.
Background Information:
How does the immune system function? The human immune system consists of specialized white
blood cells and lymphatic organs such as the spleen, thymus, and tonsils. Some white blood cells,
called macrophages, engulf and digest pathogens. One type of white blood cell, called helper T
cells, stimulate another called the cytotoxic T cells. The cytotoxic T cells are specialized to
either kill pathogens or to mark the pathogens for destruction. This type of immunity is called cell
mediated immunity.
A different type of immunity is called Antibody Mediated immunity (or
humoral immunity). All cells have very specific proteins on their cell
membrane surfaces called antigens (antibody-generating proteins).
The immune system is able to identify these protein markers (think of
them like a name tag) on cells that are foreign and to distinguish them
from its own body's proteins. Think of antigens like name tags.
Antibodies are another type of protein created by white blood cells,
called B cells, in response to antigens. Antibodies are part of the body's
defense system against disease and infection.
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Antibodies have a chemical structure that precisely “fits”
the shape of the antigen with which they react. Once the
binding between the antigen and antibody has been made
the pathogen is destroyed. The combination of an antigen
stuck to an antibody is called an antigen-antibody
complex.
Antibodies have two binding sites, so they can attach to
two antigen molecules. They deal with pathogens by
clumping or linking them together to make it easier for them to be engulfed by phagocytes. They
can also rupture foreign cells and inactivate any toxins they produce.
Some of the antibody producing cells remains in the body's immune system as memory cells.
These specialized cells can quickly mount an attack if the body is invaded again by the same
pathogen.
Pre-lab questions:
1. What is a pathogen? Provide an example.
2. What are the similarities and differences between cell mediated immunity and
antibody mediated immunity? Create a graphic organizer (concept map, t-chart,
venn diagram, etc…) using information found in the reading.
3. Antibodies are very specific to the antigen’s shape. Make a connection to two
other shape-specific proteins that have been discussed during the Living
Environment course.
4. What is the name of the “thing” that has antigens on its surface? Where are
antigens found on these “things”?
5. Where do antibodies come from?
Procedure:
1. Cut out the shapes from the last two pages of this packet. Spread the pieces out on your
desk or table.
2. Before you proceed make sure you understand what the pieces of paper represent!
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3. Find two shapes that fit together like pieces of a jigsaw puzzle. Glue the shapes in place on a
piece of scrap paper. (It does not matter where on the scrap paper you place the shapes, as
long as the shapes are joined together. Do keep in mind that you eventually will have to fit all
the shapes on the paper.)
4. Repeat step 3 until you have matched up all the shapes and attached them on the paper.
Questions:
1. What is the relationship between antigens and antibodies? Is it specific or nonspecific? Explain.
2. According to this antigen-antibody complex model you created, what seems to happen when
antibody comes in contact with an antigen? Hint: Look at the shape of an antibody compared to that
of an antigen.
3. What are two ways in which the actions of an antibody are helpful in preventing disease or
infection?
4. Sometimes it takes time for white blood cells (B cells) to produce antibodies needed to attack an
antigen. What would you be experiencing while waiting for the antibodies to be produced?
5. Sometimes white blood cells "remember" how to make a certain type of antibody, and thus produce
antibodies immediately. If this were the case in your body, what would happen if you were exposed
again to the pathogen (contains previously identified antigen) that these antibodies were designed to
fight?
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