Topic 2.4 - Cell Recognition & Immune System Flashcards
What is an antigen? (2)
- Foreign molecule / protein
- That stimulates an immune response leading to production of an antibody
How are cells identified by the immune system? (2)
- Each type of cell has specific molecules on its surface
- Often proteins -> have a specific tertiary structure
What types of cells and molecules can the immune system identify? (4)
1) Pathogens
2) Cells from other organisms of the same species
3) Abnormal body cells
4) Toxins
Describe phagocytosis of pathogens (non-specific immune response) (5)
1) Phagocyte recognises foreign antigens on pathogen
2) Phagocyte engulfs pathogen by surrounding it with its cell membrane
3) Pathogen contained in phagosome
4) Lysosome fuses with phagosome and releases lysozymes
5) Lysozymes hydrolyse pathogen
Describe the response of T lymphocytes to a foreign antigen (cell mediated response) (1+3)
Specific T helper cells with complementary receptors bind to antigen on antigen presenting cell -> activated and divide by mitosis to form clones which stimulate:
- Cytotoxic T cells -> kill infected cells / tumour cells (by producing perforin)
- Specific B cells -> humoral response
- Phagocytes -> engulf pathogens by phagocytosis
Describe the response of B lymphocytes to a foreign antigen (humoral response) (3+3)
1) Clonal selection:
- Specific B lymphocyte with complementary receptor binds to antigen
- This is then stimulated by helper T cells
- So divides by mitosis to form clones
2) Some differentiate into B plasma cells -> secrete large amounts of antibody
3) Some differentiate into B memory cells -> remain in blood for secondary immune response
What are antibodies? (3)
- Quaternary structure proteins (4 polypeptide chains)
- Secreted by B lymphocytes
- Bind specifically to antigens forming antigen-antibody complexes
Explain how antibodies lead to the destruction of pathogens (4)
1) Antibodies bind to antigens on pathogens forming antigen-antibody complex
2) Each antibody binds to 2 pathogens at a time causing agglutination (clumping) of pathogens
3) Antibodies attract phagocytes
4) Phagocytes bind to the antibodies and phagocytose many pathogens at once
Explain the process of primary immune response (1+3)
Primary - First exposure to antigen
1) Antibodies produced slowly at a lower concentration
2) Takes time for specific B plasma cells to be stimulated to produce specific antibodies
3) Memory cells produced
Explain the process of Secondary immune response (1+2)
Secondary - Second exposure to antigen
- Antibodies produced faster at a higher concentration
- B memory cells rapidly undergo mitosis to produce plasma cells which produce antibodies
What is a vaccine? (2)
- Injection of antigens from (dead/inactive) pathogens
- Stimulating formation of memory cells
Explain how vaccines provide protection to individuals against disease (7)
1) Specific B lymphocyte with complementary receptor binds to antigen
2) Specific T helper cell binds to antigen-presenting cell and stimulates B cell
3) B lymphocyte divides by mitosis to form clones
4) Some differentiate into B plasma cells which release antibodies
5) Some differentiate into B memory cells
6) On secondary exposure to antigen, B memory cells rapidly divide by mitosis to produce B plasma cells
7) These release antibodies faster and at a higher concentration
Explain how vaccines provide protections for populations against disease (3)
1) Herd immunity - large proportion of population vaccinated, reducing spread of pathogen
2) Large proportion of population is immune so do not become ill from infection
3) Fewer infected people to pass pathogen on
Key features of Active Immunity (5)
1) Initial exposure to antigen e.g. vaccine
2) Memory cells involved
3) Antibody produced and secreted by B plasma cells
4) Slow, takes longer to develop
5) Long term immunity
Key features of Passive Immunity (5)
1) No exposure to antigen
2) No memory cells involved
3) Antibody introduced from another organism
4) Faster acting
5) Short term immunity
Explain the effect of antigen variability on disease and disease prevention (2+2)
1) Antigens on pathogens change shape / tertiary structure due to gene mutations
2) So no longer immune
- B memory cell receptors cannot bind to changed antigen on secondary exposure
- Specific antibodies not complementary / cannot bind to changed antigen
Describe the replication of HIV in helper T-cells (7+2)
1) HIV attachment proteins attach to receptors on helper T cell
2) Lipid envelope fuses with cell-surface membrane, releasing capsid into cell
3) Capsid uncoats, releasing RNA and reverse transcriptase
4) Reverse transcriptase converts viral RNA to DNA
5) Viral DNA inserted into helper T cell DNA
6) Viral protein / enzymes are produced
A. DNA transcribed into HIV mRNA
B. HIV mRNA translated into new HIV proteins
7) Virus particles assembled and released from cell
Explain how HIV causes the symptoms of AIDS (3+2)
1) HIV infects and kills helper T cells as it multiplies rapidly
- So T helper cells can’t stimulate cytotoxic T cells, B cells and phagocytes
- So B plasma cells can’t release as many antibodies for agglutination & destroy pathogens
2) Immune system deteriorates -> more susceptible to infections
3) Pathogens reproduce, release toxins and damage cells
Why are antibiotics ineffective against viruses? (2)
- Viruses do not have metabolic processes / ribosomes
- Viruses do not have bacterial enzymes
What is a monoclonal antibody?
- Antibody produced from cloned B lymphocytes
- So have the same tertiary structure
Explain how monoclonal antibodies can be used in medical treatments? (4)
- Monoclonal antibody has a specific tertiary structure / binding site
- Complementary to receptor / antigen only found on a specific cell type
- Therapeutic drug attached to antibody
- Antibody binds to specific cell, forming antigen-antibody complex, delivering drug
Explain how monoclonal antibodies can be used in medical diagnosis (4)
- Monoclonal antibody has a specific tertiary structure / binding site
- Complementary to specific receptor / antigen associated with diagnosis
- Dye / stain / marker attached to antibody
- Antibody binds to receptor / antigen forming an antigen-antibody complex
