Chapter 5- Cell Recognition And Immune System Flashcards
What is a pathogen? Name an example.
A microorganism that causes infectious diseases.
E.g. Virus, bacteria, protists, fungi
What is a toxin?
A poisonous substance produced by a living organism.
Animals can produce toxins to kill prey.
What is an antigen?
- refer to genetic mutations.
A foreign molecule (protein) that stimulates an immune response.
- Genetic mutations in a pathogen can cause antigens to change… therefore a person has to launch an new immune response.
The Immune response 1
Describe the process of phagocytosis.
- Phagocyte is attracted to pathogen by chemicals.
- Phagocyte has many receptors on membrane, these attach to chemicals on pathogen
- Lysosomes migrate towards phagosome (formed via engulfing pathogen)
- Lysosomes release lysozymes which hydrolyse the pathogen
- Products are then absorbed by phagocyte.
The Immune response 2
Describe the cellular response
- After phagocytosis, the phagocyte contains debris from the hydrolysed pathogen
- It contains a useful antigen, which is moved towards the cell membrane of the phagocyte
- Only 1 Helper T cell receptor fits antigen via process of clonal selection
- Mitosis allows cloning of helper T cell so many activated cytotoxic helper T cells are produced
What do helper T cells do after cellular response?
- become memory cells: these circulate in blood ready to respond to future infection by same pathogen
- Stimulate B cells to divide
- stimulates phagocytosis
- Activates cytotoxic cells which kill infected cells by making holes in membranes of them
The Immune Response 3
Describe the humoral response
It uses B cells that are stimulated to divide from cellular response
- B cell has specific receptor for that antigen. It engulfs the pathogen using this
- A vesicle forms round the pathogen and lysozymes hydrolyse it
- Processed antigen is then portrayed on outside of B cell
- Helper T cell binds to B Cell and stimulates clonal selection of B cells by mitosis
- These B Cells produce plasma cells and memory cells
What do plasma and memory cells do?
Primary response - Plasma Cells attach to antigens on pathogens to destroy it via secreting antibodies
Secondary response - Memory cells circulate in blood ready to respond to future infection by same pathogen
- they do this by dividing into plasma cells.
What is an antibody? Label structures
A protein able to bind to a specific antigen. They are secreted by plasma cells.
- Variable region - specific amino acid sequence
- Antigen binding site
- Light and heavy polypeptide chain
- Hinge region - disulfide bridge
- Chain of sugar molecules
How do antibodies destroy antigens?
- Agglutination - antibodies each bind to an antigen on 2 separate pathogens, causing them to clump via a network of antigen-antibody complexes
- Subsequent phagocytosis - the clump makes it easier for phagocytes to locate pathogens - antibodies serve as marker.
Differences between active and passive immunity [3]
- In ACTIVE antibodies are secreted by plasma cells whereas in PASSIVE antibodies are introduced into body from outside
- ACTIVE is longer term as memory cells are developed whereas PASSIVE is shorter term because no memory cells are created.
- ACTIVE takes longer to develop whereas PASSIVE is fast acting
Examples of active and passive immunity
ACTIVE:
Natural - normal immune response
Artificial - vaccination
PASSIVE:
Natural - antibodies from placenta to foetus
Artificial - anti-venom
How does vaccination work? - non exam style
- vaccines contain isolated antigen molecules, dead pathogens or live but attenuated (weakened) pathogens. However must still have required antigen on surface
- when injected: leads to primary response and memory cells are made
- on second exposure- memory cells bind to antigen and:
- Rapidly divide into plasma cells which leads to a faster production of antibodies at a higher concentration.
What is herd immunity?
- form of indirect protection from infectious disease.
- occurs when a sufficient % of population are immune to infection (through vaccination) which results in a reduced chance of infection for those who lack immunity.
Why is herd immunity important?
IMPOSSIBLE TO VACCINATE EVERYONE:
- infants immune system is still developing
- some people are very ill and can’t be vaccinated
- allergies
- ethical/religious obligations
What makes a successful vaccination programme? [5]
- economically viable to produce on large enough scale
- easy to administer
- few side effects
- easy to achieve herd immunity
- means to produce, store and transport vaccine
Why can vaccines fail to eliminate disease?
- defective immune systems
- catch disease too soon after
- antigen variability
- many types of pathogen for same disease
- some pathogens hide from immune system
- ethical/religious obligations
List some potential problems with vaccines
- inactive microorganisms may become active
- attenuated microorganisms may mutate and become harmful
- non pathogenic microorganisms may mutate and become harmful
- genetic info/ protein in it may harm cells
- vaccine not effective against all strains of pathogen
- false positives
What is a monoclonal antibody?
Antibodies with the same tertiary structure produced from a genetically identical set of plasma cells.
- all bind to same antigen
List the 2 main medical uses of monoclonal antibodies?
- Targeting medication to specific cell types by attaching therapeutic drug to antibody.
- deliver cytotoxic drugs to cancer cells which kill them - Medical diagnosis: e.g. a pregnancy test identifies presence of a pregnancy hormone (hCG) in urine sample.
Ethical issues with monoclonal antibodies use.
- they are made using mice that have to be given cancer
- potential to cause side effects that may be serious even if shown to be safe in LAB animals.
EXAM STYLE QUESTION
How are pathogens destroyed by phagocytosis? 4 marks
- Phagocyte attracted by substance;
- Pathogen engulfed;
- Enclosed vesicle/ phagosome;
- Phagosome fuses with lysosome;
- Lysosome contains lysozymes;
- Pathogen digested/ hydrolysed;
EXAM STYLE QUESTION
Explain why antibodies bind to a specific antigen. 3 marks
- Antibody variable region has specific amino acid sequence;
- Shape/ tertiary structure of binding site is complementary to antigens;
- Forms antigen- antibody complex;
EXAM STYLE QUESTION
Describe how phagocytosis of a virus leads to the presentation of it’s antigens. 3 marks
- Phagosome fuses with lysosome;
- Virus destroyed by lysozymes;
- Antigens are displayed on the cell membrane;
EXAM STYLE QUESTION
Describe how the presentation of antigens leads to secretion of antibodies. 3 marks
- Helper T cell binds to antigen on phagocyte;
- This helper T cell stimulates a specific B cell to divide;
- B cell divides by mitosis;
- It forms plasma cells that release antibodies;
EXAM STYLE QUESTION
Why do vaccines need to be refrigerated?
- antigens are proteins
- high temperature will break ionic/ hydrogen bonds in protein
- antigen will denature
- results in no immune response.
EXAM STYLE QUESTION
Describe how B lymphocytes would respond to vaccination against a virus. 3 marks
- B cell binds to viral antigen;
- B cells divides by mitosis;
- Plasma cells release antibodies;
- B cells produce / develop into memory cells;
EXAM STYLE QUESTION
Explain how vaccination would lead to a person developing immunity to a pathogen. 5 marks
- Vaccine contains antigen/ attenuated / dead pathogens;
- T cells activate B cells;
- B cells divide by mitosis;
- Plasma cells produce antibodies;
- Memory cells produced meaning more antibodies in secondary response;
How do viruses (HIV) replicate?
- Attachment proteins attach to receptors on helper T cell
- RNA enters the cell
- Reverse transcriptase converts RNA to DNA
- Viral protein produced
- virus assembles and released from cell
EXAM STYLE QUESTION
Describe how HIV is replicated once inside helper T cells [4marks]
- RNA is converted into DNA using reverse transcriptase
- DNA inserted into helper T cell DNA
- DNA is transcribed into HIV RNA
- This is then translated into viral proteins
Describe the role of antibodies in producing a positive result in the ELISA test [4]
- First antibody binds to antigen
- Second antibody with enzyme attached is added
- Second antibody attaches to the antigen
- This causes a colour change
