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Flashcards · 9700 · AS Topic 11
Immunity (AS Level) flashcards
13 cards on AS Topic 11, subtopics 11.1 to 11.2. Pick a subtopic or study them all.
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11.1 The immune system
- Antigen, and self vs non-self
- An antigen is a molecule (usually a protein or glycoprotein) recognised by the immune system that stimulates an immune response. Self antigens are on your own cells and normally trigger no response; non-self antigens do.
- Steps of phagocytosis
- Chemotaxis → receptors bind the pathogen → the membrane engulfs it (endocytosis) into a phagocytic vacuole → lysosomes fuse and release hydrolytic enzymes → the pathogen is digested.
- Neutrophils vs macrophages
- Neutrophils: lobed nucleus, short-lived, first to arrive; engulf and digest. Macrophages: develop from monocytes in tissues, long-lived; engulf and digest, and present antigens to lymphocytes.
- T-helper cell vs T-killer cell
- T-helper: binds presented antigen, divides and releases cytokines that activate B-cells and T-killer cells. T-killer: binds to infected body cells showing the antigen and kills them. Neither makes antibodies.
- Clonal selection and clonal expansion
- Clonal selection: only lymphocytes with receptors complementary to the antigen are activated. Clonal expansion: the selected lymphocytes divide by mitosis to form a clone.
- Primary vs secondary immune response
- Primary: first exposure; few matching lymphocytes; delay of several days; low antibody peak; usually symptoms. Secondary: many memory cells; short delay; much higher peak; pathogen usually destroyed before symptoms.
- Plasma cell
- A cell formed from a B-lymphocyte, with lots of rough ER and Golgi, that secretes antibodies. Short-lived, unlike memory cells.
11.2 Antibodies and vaccination
- Structure of an antibody
- Two heavy and two light polypeptide chains joined by disulfide bonds (Y shape). Variable regions form two antigen-binding sites complementary to one antigen; a hinge gives flexibility; the constant region binds receptors on phagocytes.
- Ways antibodies help destroy pathogens
- Agglutination (two binding sites clump pathogens); neutralising toxins; blocking the sites viruses use to enter cells; marking pathogens for phagocytes via the constant region.
- How are monoclonal antibodies made?
- Inject a mouse with the antigen; remove its antibody-making B-lymphocytes; fuse them with myeloma cells to form hybridoma cells; select the hybridoma making the required antibody and clone it. Myeloma cells let the hybrid divide indefinitely.
- Principle of using monoclonal antibodies in diagnosis and treatment
- Diagnosis: an antibody carrying a marker binds only where its antigen is (for example hCG in pregnancy tests). Treatment: it binds a specific antigen on target cells, blocking a receptor, marking cells or delivering a drug.
- Active vs passive immunity, natural vs artificial
- Active (own antibodies and memory cells, long-term): natural = infection; artificial = vaccination. Passive (antibodies from outside, no memory, short-term): natural = placenta or breast milk; artificial = antibody injection.
- Vaccine and herd immunity
- A vaccine contains antigens and causes a primary response without disease, producing memory cells. Herd immunity: so many people are immune that transmission breaks down, protecting unvaccinated people too.