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lectures 20, 23, and 25 biology

lectures 20, 23, and 25 biology - Lecture 20...

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Lecture 20 Multicellularity: Immune Systems Defending Self from Nonself Where We’re Going 1) Innate Responses 2) Acquired – specificity 3) Acquired – diversity 4) Acquired – self vs nonself 5) Acquired – memory Innate Responses Characteristics: phylogenetically ancient, broad spectrum responses, limited # of recognition molecules, no lasting protection or memory 1) Physical anatomical barriers a. Structures: waxy cuticle, skin, mucus membranes b. Secretions: sap flow, mucus, exfoliating bark 2) Physiological barriers (temperature pH, oxygen tension) 3) Chemical Responses (complement proteins , lysozyme, interferons, defensins) a. Complement proteins: about 30 types b. Lysozyme: enzyme that cleaves peptidoglycans c. Interferons: viruses d. Antimicrobial peptides (defensins, bacteria) 4) Inflammation: release of histamine from mast cells, capillary response, local swelling heart a. Damaged tissues release histamines increasing blood flow to area b. Histamines cause capillaries to leak, releasing phagocytes and clotting factors into wound c. Phagocytes engulf bacteria, dead cells, and cellular debris d. Platelets move out of the capillary to seal the wounded area 5) Cellular responses: mobile phagocytic cells, natural killer, etc Acquired Immune Responses -Characteristics: evolutionary derived (known so far from vertebrate animals) high specificity , diversity of recognition, self vs nonself , memory : ability to remember prior exposure -Components of human immune system: blood, lymph, lymphatic ducts/nodes (neck/shoulders), spleen (abs), bone marrow (thigh), thymus (chest) -Invaders are, or create antigens with a variety of different epitopes …host produces antibodies (proteins) that recognize specific epitopes -B Cells: 2 heavy chains, 2 light chains with tip: variable and base: constant -Cytotoxic or helper Cell: 1 alpha, 1 beta (variable at top) -proteins composed of 2 identical subunits: each with light and heavy chain Host produces antibodies (proteins) that recognize specific epitopes constant part -variable part transmembraneregion identical binding sites on two arms of Y (about 100,000 copies per cell) similar to immunoglobulinsor antibodies (except for transmembraneregion) diversity across cells (106B-cell types, 107 T-cell types) Antigens are presented to killer T cell receptors by MHC 1 proteins (MHC found
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on all cells, recognized by cytotoxic) Antigens are presented to helper T cell receptors my MHC II Proteins …found only on dendritic cells , macrophages, or B cells. MHC I and II are polymorphic (variable in population Some people are able to discriminate odor of others based on array of MHC molecules -diversity conundrum: how can human genome code for millions of b-cell and t- cell receptors and antibody proteins -gene economy: assemble receptor proteins from subunits (no need for multiple genes) -variable regions: combinatorial diversification DNA rearrangement and RNA splicing of immunoglobin (Ig) genes 1) DNA deleted between randomly selected segments by recombinase 2) Function gene transcription 3) RNA processing 4) Translation Y shape is adaptive
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