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73 Cards in this Set
- Front
- Back
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Antigen (Definition) |
Any substance that binds specifically to an antibody or a T cell receptor |
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Antibody (Ab) (Definition) |
A protein produced by B cells that binds specifically to an antigen; may be on surface of B cells or secreted as soluble proteins |
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"Antibody" is synonymous with ____ |
Immunoglobulin (Ig) |
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T cell antigen receptor (TCR) (Definition) |
A complex of proteins on the surface of T cells that binds specifically to peptide antigens that are bound to a major histocompatability complex (MHC) protein on the surface of other cells |
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Immunogen (Definition) |
A substance that can elicit an immune response; usually compromises multiple antigens |
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Are all immunogens antigens? |
Yes |
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Are all antigens immunogens? |
No |
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Epitope (Definition) |
The site on an antigen that directly contacts the antigen-binding pocket of an antibody or T cell receptor |
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"Epitope" is synonymous with ____ |
Antigenic determinant |
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Hapten (Definition) |
A low-molecular weight compound that can act as an epitope but is not immunogenic unless coupled to a larger carrier molecule |
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What determines immunogenicity? |
Foreignness
High molecular weight
Chemical complexity |
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Why are high molecular weight molecules more immunogenic? |
They have more potential epitopes |
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What class/es of macromolecules do T cells respond to? |
Proteins |
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What class/es of macromolecules do B cells respond to? |
Proteins
Polysaccharides
Lipids
Nucleic acids
Lipopolysaccharides (lipids + polysaccharides) |
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Why do combinations of classes of macromolecules (glycoproteins, proteoglycans, and lipoproteins) have high immunogenicity? |
They bind to both B and T cells
(↑ complexity) |
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What determines an individual's immune repertoire (of B and T cells)? |
Antigens encountered during the lifetime of an individual |
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Each individual possesses a ____ but ____ immune repertoire |
Unique but overlapping |
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Binding of an antigen to cell surface receptors causes cell ____ and ____ into memory cells and effector cells, a process called clonal selection |
Proliferation and differentiation |
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Relationship between membrane bound Ig and secreted antibodies |
Secreted antibodies have the same antigen specificity as the membrane bound Ig expressed by their B cell precursors |
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What are the components of an immunoglobulin/antibody? |
A pair of identical heavy chains and a pair of identical light chains |
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How are the various chains of an immunoglobulin/antibody held together? |
Disulfide bonds |
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Where is the antigen-binding site of an Ig/Ab located? |
At the N-terminus |
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Where is the transmembrane/hydrophobic region of a membrane bound Ig located? |
At the C-terminus of the heavy chain |
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What are the variable regions of an Ig/Ab? |
The N-terminus regions of the heavy and light chains |
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What are the constant regions of an Ig/Ab? |
The C-terminus regions of the heavy and light chains |
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Why is it significant that Ig/Ab are divalent (have two binding sites)? |
Allows cross-linking of antigens to form immune complexes |
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What do the variable regions of Ig/Ab confer? |
Ag-specific binding |
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What do the constant regions of Ig/Ab confer? |
Specific immune effector functions |
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Immunoglobulin domains (Definition) |
Tightly folded domains in the polypeptide chains of the Ig molecule that are connected by short linear segments; are the functional regions of the Ig |
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Where do heavy and light chains associate with each other? |
At corresponding Ig domians |
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What does the association of corresponding heavy and light chain Ig domains form? |
A unique antigen-binding pocket |
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How do the highly variable regions of the heavy and light chains come together to form an antigen-binding site? |
Protein folding |
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Uses of proteolytic fragments of immunoglobulins |
Diagnostic markers
Therapeutic agents |
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Papain (Function) |
Cleaves immunoglobulins, separating two Fab fragments from an Fc fragment |
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Fab fragment (Definition) |
A monovalent fragment of an immunoglobulin; can bind a single antigen |
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Fc fragment (Definition) |
C-terminal region of heavy chain; can be crystallized |
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Pepsin (Function) |
Cleaves immunoglobulin, producing F(ab')₂ fragment and degrading the Fc region |
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F(ab')₂ fragment (Definition) |
A divalent fragment of an immunoglobulin; can still bind two antigens |
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Linear epitope (Definition) |
A linear sequence of amino acids recognized by an antibody |
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Discontinuous (conformational) epitope |
A discontinuous sequence of amino acids recognized by an antibody; can be destroyed by denaturation |
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Multivalent antigen (Definition) |
An antigen with multiple epitopes |
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Most B-cell epitopes are _____ epitopes |
Discontinuous |
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Affinity (Definition) |
The strength of binding between an antibody and antigen |
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What determines affinity of antibody-antigen binding? |
Non-covalent interactions between a single antigen-binding site on the antibody and the epitope on the antigen |
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Avidity (Definition) |
The accumulated strength of multiple affinities of individual non-covalent binding interactions |
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How is the avidity of antigen-antibody binding increased? |
Cooperativity among antigen-binding sites on the same antibody molecule, when bound to a multivalent antigen |
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Isotype (Definition) |
Antibody class |
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What determines antibody isotype? |
The heavy chain constant region |
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Does isotype affect antigen binding? |
No |
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What does isotype affect? |
Effector functions of an antibody |
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Allotype (Definition) |
Antibody polymorphisms due to minor genetic differences among individuals |
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Does allotype affect antibody function? |
No |
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Idiotype (Definition) |
Unique sequence of antibody variable region |
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What does idiotype affect? |
Ag-binding specificity |
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What determines arm movement of immunoglobulins? |
Hinge region |
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What are the classes (isotypes) of human immunoglobulins? |
IgG
IgM
IgD
IgA
IgE |
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What classes of immunoglobulins have subclasses? |
IgG (1, 2, 3, and 4)
IgA (1 and 2) |
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Are the IgG subclasses functionally unique? |
Yes |
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Are the IgA subclasses functionally unique? |
No |
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What heavy chain is associated with each class/subclass of immunoglobulin? |
IgG = γ₁, γ₂, γ₃, and γ₄
IgA = α₁ and α₂
IgM = µ
IgD = δ
IgE = ε |
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Which class of immunoglobulin is synthesized in the highest concentrations in serum (daily)? Second highest? |
1st: IgA
2nd: IgG |
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Which class of immunoglobulin is present in highest concentrations in the serum? Second highest? |
1st: IgG
2nd: IgA |
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Which class of immunoglobulin is synthesized in the serum and doesn't leave? |
IgM |
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Which class of Ig is secreted by plasma cells as a pentamer? |
IgM |
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Pentameric IgM has higher ____ for multivalent antigens |
Avidity |
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Why does pentameric IgM only utilize 5 binding sites instead of the full 10? |
Stiff hinge region |
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Which class of Ig is secreted by plasma cells as a dimer? |
IgA |
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Is IgA in the serum mainly monomeric or polymeric? |
Monomeric |
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Is externally secreted IgA mainly monomeric or polymeric? |
Polymeric |
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What polymers can IgA form? |
Dimers, trimers, and tetramers |
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Which class of Ig is transported across epithelium into breastmilk? |
IgA, IgM (very little) |
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Which classes of Ig are transported across placenta? |
All IgG subclasses (mostly IgG1, very little IgG2) |
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Which classes of Ig diffuse into extravascular sites? |
All IgG subclasses, IgA monomers, IgE (very little) |
