Intro Bio 151-153 Discussion homework for the week of April 23 rd INSTRUCTIONS: Print this homework and complete it before going to your discussion section. Believe us – there is a lot to go over this upcoming week in discussion, and you will have a greater chance of getting through it if you really takethis homework seriously. 1. What general, or “innate,” defense mechanisms does the body use to help prevent infection by pathogens? For example, what defense mechanisms are involved in local inflammatory responses? What are some of the other “players” in innate immunity (I can think of at least 4 from lecture)? How does the body use these defenses?Epithelial Surfaces Help Prevent Infection, Human Cells Recognize Conserved Features of Pathogens, Complement Activation Targets Pathogens for Phagocytosis or Lysis, Toll-like Proteins Are an Ancient Family of Pattern Recognition Receptors. The interior epithelial surfaces are also covered with a mucus layer that protects these surfaces against microbial, mechanical, and chemical insults; many amphibians and fish also have a mucus layer covering their skin. The slimy mucus coating is made primarily of secreted mucin and other glycoproteins, and it physically helps prevent pathogens from adhering to the epithelium.Skin, saliva, 2. Review your class notes and also watch the subtitled animations via the links given below. Take note of the different “players” in the immune system and what they do (T cells [cytotoxic and helper], B cells, antibodies, antigens, etc.) as well as how the whole process works. After watching these, answer the following questions. Please note that these animations are simplified models. As such, they can omit some important details (e.g., they may show processed antigens moving through the cytoplasm of a cell, when in reality, they would be moving through the cell within a vesicle).“Antigenic Determinants (Epitopes)”:http://highered.mheducation.com/sites/0072507470/student_view0/chapter22/animation__antigenic_determinants__epitopes_.html“Antigen Processing”http://highered.mheducation.com/sites/0072507470/student_view0/chapter22/animation__antigen_processing.html “Interaction of Antigen Presenting Cells and T-helper Cells”http://highered.mheducation.com/sites/9834092339/student_view0/chapter51/interaction_of_antigen_presenting_cells_and_t-helper_cells.html “Cytotoxic T-Cell Activity against Target Cells”http://highered.mheducation.com/sites/0072507470/student_view0/chapter22/animation__cytotoxic_t-cell_activity_against_target_cells__quiz_1_.htmla. When a macrophage engulfs “EVIL” it presents the EVIL on its cell surface. What roles do Class II MHC molecules, CD4, helper T cells, T cell receptors, and cytokines play in the antibody-mediated response? Cytotoxic T cells interact with the virus-infected cells by recognizing both the viral antigen and the ClassI MHC. The T cell then releases cytotoxins which induce apoptosis in the infected cell and perforin, which causes perforations in the cell membrane. Self-proteins are also degraded and the fragments presented on the surface via Class I MHCs. Fragments of self-proteins are not recognized by cytotoxic T cells. 1b. What happens when helper T cells interact with B cells? The protein antigen is ingested and then broken down into peptide fragments by an antigen-presenting cell such as a macrophage. The antigen is then moved to the surface of the macrophage on a Class II MHC. c. Why are the plasma cells so full of endoplasmic reticulum?Abundant rough endoplasmic reticulum combined with a well-developed Golgi apparatus makes plasma cells well-suited for secreting immunoglobulins. Other organelles in a plasma cell include ribosomes, lysosomes, mitochondria, and the plasma membrane.3. What is the role played by exocytosis and endocytosis in the humoral (antibody-mediated) immune response? In otherwords, what is the path an antigen takes, starting outside the cell, moving inside the cell, and then ending up attached tothe cell membrane?Antigens bind to B cells.Interleukins or helper T cells costimulate B cells. In most cases, both an antigen and a costimulator are required to activate a B cell and initiate B cell proliferation.B cells become plasma cells. The plasma cells bear antibodies with the identical antigen specificity as the antigen receptors of the activated B cells. The antibodies are released and circulate through the body, binding to antigens.B cells produce memory cells. Memory cells provide future immunity.4. How does somatic recombination create diversity in antibodies? In your answer, consider just the light chain (but be sure you understand what also happens in the heavy chain). What other mechanisms are there for increasing diversity?The first line of defense (or outside defense system) includes physical and chemical barriers that are always readyand prepared to defend the body from infection. These include your skin, tears, mucus, cilia, stomach acid, urine flow, 'friendly' bacteria and white blood cells called