antibodies Flashcards
(18 cards)
what are antibodies?
proteins that have binding sites complementary in shape to certain antigens
what are antibodies made from?
four polypeptide chains
the chains of one pair are long and are called heavy chains, while the chains of the other pair are shorter and known as light chains
what do all antibodies have?
two specific binding sites which are complementary to the
specific antigen
this means that antibodies combine to two antigens and form an antigen-antibody complex
what is the variable region of antibodies? what about constant region?
the binding sites are different on different antibodies so is called the variable region
the rest of the antibody is called the constant region, which binds to receptors on cells such as B cells
when an antigen-antibody complex has formed, what does this mean for the pathogen?
it immobilises the pathogen so it can’t attach to host cells (agglutination)
it also makes it easier for phagocytes to engulf the pathogens (agglutination)
what does the Ag-Ab complex activate?
chemicals that lead to holes being placed in the cell membranes of cellular pathogens and in virus infected cells
these holes mean water can enter by osmosis and the cell undergoes cell lysis
how do antibodies affect toxins by binding?
they block the toxins receptor site so that they can no longer bind to cells and it causes them to precipitate out of the solution (become a solid that cannot dissolve)
what is a monoclonal antibody?
a single type of antibody that cab be isolated and cloned
what are the uses of monoclonal antibodies?
-targeted medication (direct and indirect monoclonal antibody therapy)
-medical diagnosis
-pregnancy tests
describe how direct monoclonal antibody therapy works?
-some cancer can be treated with monoclonal antibodies with a binding site complementary to the antigens on cancer cells
-antibodies are given to the cancer patient and attach to the cancer cells and this blocks the chemical signals that lead to uncontrolled division
-this means normal cells won’t be affected
describe how indirect monoclonal antibody therapy works?
-monoclonal antibodies have a cytotoxic drug attached to them
-when the antibody attaches to the cancer cells, the cytotoxic drug kills them
-monoclonal antibodies used in this way are referred to as ‘magic bullets’ and can be used in smaller doses since they target specific sites; this reduces side effects that traditional chemo may have
once urine passes through the reaction zone, how does a blue line show up in the test zone when using monoclonal antibodies for pregnancy testing?
-if HCG hormone is present in urine, it binds to the mobile HCG antibody in the reaction zone. These antibodies have blue dye attached
-the mobile antibodies pass along the stick, transporting any bound HCG with it
-the HCG hormone attached to the mobile antibodies also binds to the immobilised HCG antibodies in the test zone
-the dye that is attached to the mobile antibodies show up as a blue line in the test zone
if mobile antibodies no not bind to HCG then there is no binding to immobilised antibodies and so no blue line appears
where do mobile antibodies also continue into for the second part of pregnancy tests?
into the control zone
in the control zone there are antibodies that are able to bind to the antibodies for HCG
the binding means blue dye appears in control zone
what can monoclonal antibodies be used to test for in medical diagnosis?
-pregnancy
-influenza
-hepatitis
-chlamydia
-prostate cancer
-HIV
what test do we use monoclonal antibodies for in medical diagnosis?
ELISA test (enzyme linked immunosorbent essay)
it uses antibodies to detect which antigens and the quantity of antigens in a sample
when using the ELISA test to test for HIV, what is done once the HIV antigens are applied to the solid surface (surface of the well)?
-wash surface/ wells to remove any unattached HIV antigens
-add the sample from the patient being tested for HIV and leave time for binding to occur
-if the sample contains antibodies to HIV then these antibodies will bind to the antigens because they have complementary shapes
-any other antibodies in the patients sample will not be complementary to the HIV antigens and so will not bind (TEST IS HIGHLY SPECIFIC)
once binding has occurred using the ELISA test, what is done?
-wash surface/ well to remove any unbound antibodies
-add the second antibody that is able to bind to HIV antibodies
-this is a monoclonal antibody that has an enzyme attached
-allow time for binding to occur
-wash surface/wells to remove unbound antibodies
when the substrate is added during the ELISA test, what happens?
the enzyme acts on the substrate to change it from colourless to a coloured product
the presence of colour indicates presence of HIV antigen and intensity of colour = quantity of antigen
