5.5 - Antibodies Flashcards
What are antibodies
- proteins with specific binding sites synthesised by B cells
Describe how an antibody reacts with an antigen
- Binds to them on the surface of the non-self material
- each antibody has 2 identical binding sites
- the antibody identity sites are complementary to a specific antigen
What makes the variety of antibodies possible
- they’re made of proteins
Describe the structure of an antibody
- made up of 4 polypeptide chains, the chains of one pair = long (called heavy chains), while the chain of the other pair = shorter (called light chains)
- specific binding site for each antibody, fits precisely to the antigen to form: antigen-antibody complex
- the different binding sites on each antibody is known as: variable region
- each binding site consists of a sequence of amino acids that form the specific 3D shape that binds directly to a specific antigen
- the rest of the antibody is known as the constant region, its the same for all antibodies. It binds to the receptors on cells such as B cells
How does the antibody lead to the destruction of the antigen
antibodies don’t destroy antigens, but prepare the antigen for destruction in a different range of ways for each antibody
- e.g.: when the antigen is a bacterial cell - antibodies assist in its destruction in 2 ways:
1) agglutination - clumps of bacterial cells are formed, making it easier for the phagocytes to locate them (because they’re less spread-out within the body)
2) They then serve as markers that stimulate phagocytosis to engulf the bacterial cells to which they are attached
What’s the importance of the variable regions
It’s the variable region that will determine the antigen specificity, giving a specific response
What type of protein is an antibody
Antibody is an example of globular proteins
Explain how a change in the primary structure of a globular protein may result in a different 3D structure, and the consequence of this on the immune response (5 marks)
- Primary structure is the sequence of amino acids
- Determines positioning of bonds and therefore tertiary structure
- This determines shape of variable region of antibody
- which is specific/complementary to one type of antigen
- change in the variable region = the antigen can no longer bind/no antigen-antibody complex formed
- Pathogen can no longer be formed
When is neutralisation used
Some pathogens make us ill by producing toxins
—> some antibodies work by neutralising these toxins
What is a complement cascade
- the binding of an antigen to the surface of a pathogen can set off a chain reaction with blood proteins
- which causes the pathogen to swell up and burst
What are the 3 ways that antibodies work
- Agglutination
- Neutralisation
- Complement cascade
What are monoclonal antibodies
- antibodies produced from a single group of genetically identical (cloned) B-cells
- therefore, they’re all identical in structure
Are antibodies specific?
- yes
- their binding sites have a uniques tertiary structure that only one particular antigen will fit into
What are the uses of monoclonal antibodies
- Cancer treatment (both direct and indirect)
- Medical diagnosis / ELISA
- Pregnancy testing
How can monoclonal be used for cancer treatment
- monoclonal antibodies can be used to target specific substances, e.g. cancer cells
- therefore they can be used in many different ways to treat cancer:
1) direct monoclonal antibody therapy, e.g. Herceptin
2) indirect monoclonal antibody therapy,
Explain direct monoclonal antibody therapy
- monoclonal antibodies are produced that are specific to antigens on cancer cells
- These antibodies are given to a patient and attach themselves to the receptors on their cancer cells
- They attach to the surface of their cancer cells and block the chemical signals that stimulate their uncontrolled growth
Give an example for a monoclonal antibody used in direct monoclonal antibody therapy
Herceptin
- treats breast cancer
What is the advantage to direct monoclonal antibody therapy
- antibodies are not toxic
- antibodies are highly specific
—> leads to fewer side effects, than other forms of therapy
Explain indirect monoclonal antibody therapy
- attaching a radioactive or cytotoxic drug (a drug that kills cells) to the monoclonal antibody
- when the antibody attaches to the cancer cells = kills them
Why are monoclonal antibodies used in indirect monoclonal antibody therapy sometimes referred to as ‘magic bullets’
- used in smaller doses, as they target only specific sites
- this is not only cheaper, but also reduces any side effects that the drug may have
Which diseases can be diagnosed using monoclonal antibodies
- influenza
- hepatitis
- chlamydia
—> produces a much more rapid result than conventional methods for diagnosis
How can monoclonal antibodies be used to diagnose prostate cancer
- men with prostate cancer produce more of a protein called prostate specific antigen (PSA), leading to unusually high levels of it in the blood
- by using the monoclonal antibodies that interacts with this antigen = obtain a measure of the level of PSA in a sample of blood
- whilst higher than normal levels of PSA in the blood isn’t diagnostic of the disease, it does give early warnings and the need for further tests
How are monoclonal antibodies used in pregnancy testing
- placenta produces hormone: human chorionic gonadatrophin (hCG)
- hCG can be found in the mothers urine
- monoclonal, antibodies present on the test strip of a home pregnancy testing kit are linked to coloured particles
- if hCG present in urine it will bind to these antibodies
- the hCG-antibody-colour complex moves along the strip until its trapped by a different type of antibody
—> creating a coloured line - they will also create a second line at the bottom, regardless of whether hCG is present or not (acts as a control, showing if the test is faulty or not)
