1.What are the 2 general types of DNA sequences that regulate the transcription
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Question
1.What are the 2 general types of DNA sequences that regulate the transcription immunoglobulin genes? 12 marks] of 2. Is platelet derived growth factor [PDGFI a member of the immunoglobulin superfamily ? Yes or No [1 mark] Justify your answer [ ie: explain why you a way you did]I 2 marks] 3. With respect to B-cell biology, why are CD40/CD40L interactions important ? [4 marks] 4. Is the entire MAC complex absolutely required for effective cytolysis to occur? Yes or No? [1 mark]. Justify your answer. [2 marks] 5. In precipitation reactions, what specific factors determine the antigen-antibody lattice ? 16 marks]Explanation / Answer
1. There are two separate genes encode a single immunoglobulin heavy or light chain, one gene for the V region (variable region) and the other for the C region (constant region). Thus two genes must come together at the DNA level to regulate the transcription and translated into a single Ig heavy or light chain. This two gene model was proposed by Dreyer and Bennett.
2. The PDGF receptor, which is a member of the immunoglobulin superfamily (IgSF) controls cell proliferation and participate in cell cycle regulation.
3. CD40 receptor, a member of the tumor necrosis factor receptor family, is expressed by B cells. CD40 binds its ligand CD40L, which is transiently expressed on activated T cells. Hence interaction between CD40 and CD40L is essential for T cell-dependent B-cell activation. T cells expressing CD40L can provide signals to B cells that induce proliferation, immunoglobulin isotype switching, antibody secretion and rescue from apoptosis at different times during the life of a B cell. This signal also has a role in the development of germinal centres (GC) and the survival of memory B cells.
4. Membrane attack complex refers to the association of the complement proteins C5, C6, C7, C8, and C9 to form a potentially cytolytic complex. Not necessarily, entire MAC complex required for effective cytolysis. However, C5b-C9, termed as the complement membrane attack complex is responsible for the cytolytic function of complement, a potent mechanism contributing to innate defence against pathogens.
5. When both antibodies and their corresponding antigens are present in a solution, during precipitation reaction, antibodies bind more and more antigens together, resulting in a visible precipitin, or forming large complexes (lattices) that precipitates out of solution. Most precipitin tests use a polyclonal antiserum rather than monoclonal antibodies because polyclonal antibodies can bind to multiple epitopes on an antigen, making lattice formation more likely. Although monoclonal antibodies may bind some antigens, the binding will occur less often, lattice formation is much less likely.
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