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Questions and Answers
Which immunoglobulin class is characterized as a pentamer?
What does the papain enzyme digest immunoglobulin into?
Which heavy chain class is associated with IgE?
In multiple myeloma, which immunoglobulin is most commonly overproduced?
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What type of immunoglobulin structure does IgA primarily exist in its secretory form?
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Which process does not occur with IgD in terms of placental transfer?
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Bence Jones proteinuria is typically found in patients with which type of myeloma?
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What is the main function of immunoglobulins?
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How many antigen binding sites does each antibody have at a minimum?
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What distinguishes the different classes of heavy chains in immunoglobulins?
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What is the molecular weight of light chains in immunoglobulins?
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Which of the following describes the structure of an immunoglobulin?
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Which immunoglobulin classes are identified by Greek letters?
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What type of chains can light chains in immunoglobulins be classified into?
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Where is the antigen binding site located in an immunoglobulin molecule?
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Study Notes
Immunoglobulins (Antibodies)
- Glycoproteins in the plasma's gamma globulin fraction
- Produced by B-lymphocytes (plasma cells) in response to antigens
- Each antibody has at least two antigen-binding sites
Basic Unit (Monomer) of Immunoglobulin
- Four polypeptide chains: two identical heavy chains and two identical light chains
- Resembles a Y-shaped tetramer
Heavy Chains (H)
- Molecular weight: 50-75 kDa (400 amino acids)
- Identify five different immunoglobulin classes (isotypes): IgG, IgA, IgM, IgD, and IgE
Light Chains (L)
- Molecular weight: 23 kDa (212 amino acids)
- Two types: κ (kappa) and λ (lambda)
- Both κ and λ chains are present in all immunoglobulin classes
Disulfide Bonds
- Interchain bonds: Between H chains (H-H) and between H and L chains (H-L)
- Intrachain bonds: Within an individual chain
IG Domains
- Each H chain has four or five domains: one variable region (VH) and three or four constant regions (CH1, CH2, CH3, and CH4)
- Each L chain has two domains: one variable region (VL) and one constant region (CL)
Antigen Binding Site (Paratope)
- The area of the immunoglobulin molecule that interacts specifically with the epitope of the antigen
- Formed by the paired VH and VL domains at the ends of the two arms of the Y tetramer
Immunoglobulin Classes
- IgG: Monomer, γ(Gamma) heavy chain, passes placental transfer
- IgM: Pentamer, μ (Meu) heavy chain, does not pass placental transfer
- IgA: Monomer (serum) and dimeric (secretory), α (alpha) heavy chain, does not pass placental transfer
- IgD: Monomer, δ (delta) heavy chain, does not pass placental transfer
- IgE: Monomer, ε (epsilon) heavy chain, does not pass placental transfer
Immunoglobulin Digestion
- Two enzymes digest immunoglobulin molecules:
- Papain Enzyme: Digests into 2 antigen-binding fragments (2 Fab) and 1 crystallizable fragment (Fc)
- Pepsin Enzyme: Digests into 1 antigen-binding fragment F(ab)2 and digested fragments of Fc
Clinical Correlates
-
Multiple Myeloma:
- Plasma cell cancer (plasmacytoma)
- More prevalent in females
- Overproduction of abnormal Ig, primarily IgG (75%) and sometimes IgA or IgM (25%)
-
Bence Jones Proteinuria:
- Free light chain proteinuria
- Seen in patients with light chain myeloma, where monoclonal light chain expression occurs without a coexisting heavy chain
- Present in approximately 50% of IgG and IgA myeloma cases
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Description
Explore the fascinating world of immunoglobulins, the glycoproteins essential for the immune response. This quiz covers the structure, function, and types of antibodies, delving into their heavy and light chains, as well as the significance of disulfide bonds. Test your knowledge on the basic units and classifications of immunoglobulins.
