Cells (CELL RECOGNITION AND THE IMMUNE SYSTEM) Flashcards
Define antigen
An antigen is a substance foreign to the body (non self) that causes the production of antibodies from the body and causes an immune response
Define antibody
A protein with a specific binding site (due to its specific tertiary structure) complimentary to a specific antigen, synthesised and stored by plasma cells
Describe the structure of an antibody
Y shaped
Disulphide bridges
Variable region and constant region
At the 2 top ends of the Y is the specific complimentary antigen binding site
What is the body’s first line of defence and give some examples
Natural barriers that reduce the risk of infection (often exterior defences)
Eg:
Skin and membranes
Ciliated epithelium (goblet cells secrete mucus) and trap microbes in inhaled air
Acid in stomach
Sweat contains antimicrobial agents
Blood clots
Lysozyme present in tears break down bacterial cells walls (contain murein)
Describe the process of phagocytosis
The bacteria (pathogen) is attracted to the phagocyte
Pathogen gets engulfed by phagocyte which forms a phagocytic vesicle
Lysosomes fuse to vesicle
Lysozymes digest/ hydrolyse pathogen into monomers.
Antigens in bacteria surround the membrane to produce antigen presenting cell
Describe the process of cellular mediated immune response
1) Phagocytosis - forms an antigen presenting cell with antigens attached to the cell surface membrane of the phagocyte
2) Specific complimentary helper T cell binds to antigens on antigen presenting cell
3) Helper T cell undergoes clonal selection and divides by mitosis
4) This activates B cells which produces antibodies or cytotoxic T cells or memory cells
Describe what cytotoxic T cells do
Cytotoxic T cells bind to infected cell
Produce perforin which makes holes in the cell surface membrane
Infected cell lyses (dies)
Describe the process of humoral immunity
Antigens from pathogen bind to specific complimentary receptors on a B cell to form antigen presenting cell
Specific helper T helper cell activates B cell
B cell undergoes clonal selection and divides by mitosis to form memory B cells and plasma cells
Plasma cell releases antibodies and causes the agglutination of bacteria cells which causes bacteria cells to stick together and act as markers to signal phagocytes to engulf bacterial cell
Apoptosis
Describe how a pregnancy test works
Define what is meant by a monoclonal antibody
a single type of antibody produced by a single clone of plasma cells
Give some uses of monoclonal antibody’s
Treat cancers, pregnancy tests
Describe the process of direct monoclonal antibody therapy to treat cancer
- Monoclonal antibody is produced that is complimentary to the antigens on cancerous cell
- When antibody is given to patient, antibody attaches to antigen, preventing chemicals that stimulate mitosis from binding to it
Describe the process of indirect monoclonal antibody therapy to treat cancer
- A cytotoxic drug (one that kills cancer) is attached to the monoclonal antibody. This antibody has a complimentary shape to the antigens on the cancer cells
- When antibodies attach to antigen, enzyme is delivered directly to cancer cells and doesn’t kill it
–> less side effects and doesn’t damage surrounding cells
–> known as a “bullet drug” as its delivered straight to cancer cell
Explain how HIV affects the production of antibodies when AIDS develops in a person
Less antibodies are produced as HIV destroys helper T cells so less B cells can be activated
Explain how HIV replicates
HIV can only replicate inside an organism
* HIV attachment proteins bind to specific receptors called CD4 on helper T cell
* HIV capsule fuses to helper T cell membrane, injecting its RNA and reverse transcriptase enzyme
*RNA is converted into DNA through the reverse transcriptase enzyme
* DNA moves into nucleus of T cell
* DNA is transcribed into HIV mRNA.
* HIV mRNA is translated into new HIV proteins for assembly into viral particles
Explain how a vaccine works
Vaccine contains antigens of a pathogen displayed on antigen presenting cell
Antigens bind to specific complementary receptors on B cells
Helper T cell activates B cell
B cell undergoes clonal selection by mitosis to form plasma cells and memory cells
B cells produce antibodies
Vaccine contains antigen /dead/inactive pathogen;
Specific helper T cell stimulates B cell specific to antigen
B cell clones/divides by mitosis;
Plasma cells release antibodies;
Memory cells produced meaning higher concentration of antibodies/antibodies produced faster in secondary response/on infection with the actual pathogen;
Describe the ELISA tests and what it tests for
Antigens of the virus (eg: HIV antigens) are attached to the bottom of a well in a well plate
Sample of blood added with potential complimentary antibodies which will bind to HIV antigen.
Wash to remove any unbound antibody
Add a second antibody which is attached to a specific enzyme. This antibody is complimentary to the first antibody and so will only bind if the first antibody is present and bound to the HIV antigen
Wash again
A colour change will occur as the enzyme reacts
Colour change = positive result
What does a stronger colour change in the ELISA test show
Stronger colour change = higher concentration of antibodies
Describe some of the ethical considerations raised with monoclonal antibodies
–> Creating monoclonal antibodies requires mice to be injected in their spleen causing them to die for the betterment of humans
Describe active immunity
Active immunity:
–> Direct contact with the pathogen/ antigen is necessary
–> Antibodies secreted by plasma cells
–> Involves immune response and memory cells
–> Immunity is long term, but takes time to develop as antibody is produced in response to antigen
Describe passive immunity
–> No direct contact with antigen or pathogen.
–> Antibodies are introduced from an outside source
–> No memory cells formed and so no lasting immunity.
–> Immediate protection (fast acting) , but short term as antibodies are broken down
Define the term antigen variability and what does that means for vaccines
—> change of surface protein by microorganism in order to try and evade the immune system
—> vaccines need to be annually modified and updates so that the mutated microorganism does not evade the immune system
