Immunoglobulin structure, isotype classes, class switching, and affinity maturation concepts tested on USMLE Step 1.
35 cards · basic cards · AI-written, checked twice. Edit anything.
- What is the basic chain structure of an immunoglobulin monomer?
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Two identical heavy chains and two identical light chains linked by disulfide bonds- What are the two types of light chains found in immunoglobulins?
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Kappa and lambda- What region of the antibody determines its antigen specificity?
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The variable (V) region, located at the tips of the Fab arms- What region of the antibody mediates effector functions like complement fixation and Fc receptor binding?
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The constant (Fc) region of the heavy chain- What is the Fab fragment of an antibody?
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The antigen-binding fragment, containing the variable regions of one heavy and one light chain- What structure connects the two Fab arms to the Fc region and allows flexibility?
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The hinge region- Which immunoglobulin isotype is the first antibody produced in a primary immune response?
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IgM- What is the typical structural form of secreted IgM?
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A pentamer, joined by a J chain- Why is pentameric IgM particularly effective at complement fixation despite relatively low individual binding affinity?
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Its multivalent structure provides high avidity, and multiple Fc regions in close proximity efficiently activate the classical complement pathway- Which immunoglobulin isotype is the most abundant in serum and provides long-term humoral immunity?
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IgG- Which immunoglobulin isotype is the only one that crosses the placenta to provide passive immunity to the fetus?
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IgG- Which immunoglobulin isotype is the predominant antibody in mucosal secretions such as saliva, tears, and breast milk?
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IgA- What structural feature allows secretory IgA to resist degradation in mucosal secretions?
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The secretory component, added during transport across epithelial cells- What is the typical structural form of secretory IgA?
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A dimer, joined by a J chain- Which immunoglobulin isotype is bound to mast cells and basophils and mediates immediate (type I) hypersensitivity?
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IgE
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