Antibodies Flashcards
What are antibodies
proteins with specific binding site synthesised by B cells
Structure of antibody
-4 polypeptide chain
-2x long chain (heavy)
-2x short chain (light)
-each antibody has specific binding site that fits precisely onto specific antigen (antigen-antibody complex)
-binding site different on ever antibody so called variable region
-each binding site consists of a sequence of a.a that form specific 3d shape that binds directly to specific antigen
-rest of body = constant region - binds to receptors on cells eg b cells
Describe and explain how the structure of antibody relates to function
-primary structure of protein - sequence of a.a in a polypeptide chain
-determines folds in secondary structure as R groups interact
-determines specific shape pf tertiary structure and position of H , ionic and disulfide bridges
-quaternary structure comprised of 4 polypeptide chains (tertiary structured) held together by H , ionic and disulfide bridges.
enables specific shaped variable region (binding site) to form which is complimentary shape to specific antigen.
enables antibody-antigen complex to form
How antibody leads to destruction of antigen
eg bacteria cell
-binds to 2 pathogens at the same time (at variable region/binding site) forming antigen-antibody complex
-enables agglutination of bacterial cells, making it easier for phagocytes to locate them as they’re less spread-out within body
-phagocytes bind to antibodies and phagocytose many pathogens at once (serve as markers that stimulate phagocytes to engulf bacteria cellls to which they’re attached
Describe the nature of a monoclonal antibody
A single type of antibody that has been isolated and cloned
Process of monoclonal antibody therapy (treat cancer cells)
-monoclonal antibodies are produced that are specific to antigens on cancer cells
-these antibodies are given to a patient and attach themselves to receptors on their cancer cells
-they attach to the surface of their cancer cells and block chemical signals that stimulate uncontrolled growth
Advantage of monoclonal antibody therapy
since antibodies aren’t toxic and are highly specific, they lead to fewer side effects than other forms of therapy
Explain how monoclonal antibodies are produced
-Expose mouse to non-self material you need the antibody for Mouse B cells produce a mixture of antibodies which are extracted from the spleen
-Mix B cells with cells that will divide outside the body eg cancer tumour cells
-Detergent added to break cell membranes and fuse cells into hybridoma cells
-Culture each different hybridoma cell and test clone to check for required antibody
-Clone producing required antibody cloned on large scale and antibodies extracted - monoclonal antibodies
The use of monoclonal antibodies
- Monoclonal antibody = antibody produced from a single group of genetically identical (clones) B cells / plasma cells
- Identical structure - Bind to specific complimentary antigen
- Have a binding site / variable region with a specific tertiary structure / shape
- Only one complementary antigen will fit
Why are monoclonal antibodies useful in medicine
- Only bind to specific target molecules / antigens because
- Antibodies have a specific tertiary structure (binding site / variable region) that’s complementary to a specific antigen which can bind/fit to the antibody
Monoclonal antibodies: targeting medication to specific cell types by attaching a therapeutic drug to an antibody
- Monoclonal antibodies made to be complementary to antigens specific to cancer cells → cancer cells are abnormal body cells with different antigens (tumour markers)
- Anti-cancer drug attached to antibody
- Antibody binds / attaches to cancer cells (forming antigen-antibody complex)
- Delivers attached anti-cancer drug directly to specific cancer cells so drug accumulates →
fewer side effects e.g. fewer normal body cells killed
Monoclonal antibodies: medical diagnosis
Example: pregnancy test
- Pregnant women have the hormone hCG in their urine
- Urine test strip has 3 parts with 3 different antibodies
- Application area, position 1: antibodies complementary to hCG (bound to a blue coloured bead)
- Middle, position 2: antibodies complementary to hCG-antibody complex
- End, position 3: antibodies complementary to antibody without hCG attached - If pregnant
- hCG binds to antibodies in application area = hCG-antibody complex
- Travels up test strip, binds to antibodies at position 2 = blue line - If not pregnant
- No hCG in urine so hCG doesn’t bind to antibodies in application area so doesn’t bind to antibodies at position 2 = no blue line
- Bind to antibodies at position 3 → blue line = control
Ethical issues associated with monoclonal antibodies
- Animals are involved in the production of monoclonal antibodies i.e. by producing cancer in mice who have a CNS so feel pain, and it is unfair to give them a disease
- Although effective treatment for cancer and diabetes has caused deaths when used in treatment of Multiple Sclerosis
- Patients need to be informed of risk and benefits before treatment so they can make informed decisions
What is the variable region on an antibody?
the area on an antibody that contains the antigen binding site. They are different on each antibody, this is caused by the difference in the primary structure of the protein.
What is the constant region of an antibody
A
When antibodies bond to more than one pathogen causing them to clump together
