Distinguish between Antigens and Anitbodies
Antigen
It's a foreign body in the blood, it is any
molecule recognized by the anitbodies.
It is a large molecule (protein,
glycoprotein, lipoprotein or
polysaccharide) on the outer surface of
a cell.
All living ells have these antigens as
part of their cell membrane or cell wall.
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.
Antibodies
It is a globular protein that recognizes
an antigen and attaches to its surface,
forming antibody-antigen complex.
B-cells made antibodies
Is a protein molecule that can bind
specifically to an antigen.
Antibodies all have similar structure
composed of 4 polypeptide chains
joined together by strong disulphide
bonds to form Y0shaped structure
The ends of the arms of the Y are called
the variable regions of the molecule
because different immunoglobulin
molecule has different amino acud
structure ad therefore different
structures.
Antibiotics block specific metabolic pathways found in bacteria, but not in
eukaryotic cells.
Antibiotics can be selectively toxic by targeting such features as the bacterial cell
wall, 70S ribosomes, and enzymes that are specific to bacteria. In this way the human
eukaryotic cells are unaffected.
Viruses reproduce using the host cell metabolic pathways that are not affected
by antibiotics.
Viruses do not have metabolic pathways like bacteria and therefore antibiotics do not
work on viruses.
Viruses can only be treated by their specific anti-microbial agent and antibiotics
should never be prescribed for viral infections (such as flu).
Outline the principle of challenge and response, clonal selection, and memory cells as
the basis of immunity:
Challenge:
• antigens:
o substances foreign to the host
o which stimulate antibody production by B lymphocytes
Response:
• antibodies:
o immunoglobulins
§ produced during protein synthesis
§ by B-lymphocytes
o great variety of different B lymphocytes
§ about 10 to the 15th power
§ each producing its own unique antibody, specific to just one type of
antigen
• process of immunity called challenge and response
o because immunity to a disease is only produced after exposure
o to the specific antigens associated with the disease
Clonal Selection:
• initial encounter with an antigen
o produces a primary challenge and response
o including a lag time for clonal selection
o to mitotically produce many daughter lymphocytes
• B-lymphocyte proliferation
o by mitotic cloning of selected B-lymphocytes
§ selection by match of antibody to antigen
§ just one (= clonal selection)
§ or a few (=polyclonal selection)
• antibody production
o B-lymphocytes produce >1000 antibodies/second/B-lymphocyte
o each specific to the invading antigen
Memory Cells:
• initial exposure
o each clone of B-lymphocytes
§ includes immediately active, antibody-producing plasma cells
§ as well as dormant, memory cells
• subsequent exposure
o stimulates memory cells to produce a secondary response
o because of the elevated number of memory cells
o secondary response is much faster and stronger than the primary response
http://www.slic2.wsu.edu:82/hurlbert/micro101/images/immcs2.gif
Burrell, John. "Click4Biology: 6.3 Defence against Infectious
Disease." Click4Biology. Web. 18 Sept. 2011.
<http://click4biology.info/c4b/6/hum6.3.htm>.