Covers the structure of antibodies, beginning with their role in humoral immunity and how B cells produce them in membrane-bound and soluble forms. It then describes the four-chain Y-shaped molecule, its domains, the complementarity determining regions that form the antigen-binding site, and the constant region's effector functions. The note also outlines light and heavy chain isotypes, oligomeric forms such as IgA dimers and IgM pentamers, glycosylation, papain fragmentation, and monoclonal antibodies. Four mnemonics summarise chain structure, binding sites, antibody classes and papain cleavage.
Topic 48 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 15 sections, about 1,075 words (8 min of reading), with 12 flashcards.
In this note
Structure of antibodies
General Characteristics of Antibodies
Formation and Types
Basic Structure: Polypeptide Chains and Overall Shape
Chain Arrangement and Bonding
Domain Architecture
Antigen Binding Regions
Constant Region Functions
Membrane-Bound vs. Soluble Forms
Antibody Isotypes and Their Structural Variations
Oligomeric Forms
Glycosylation and Solubility
Enzymatic Fragmentation and Structural Analysis
Monoclonal Antibodies
MNEMONIC
Structure of antibodies
Structure of Antibodies (Immunoglobulins)
General Characteristics of Antibodies
Antibodies, scientifically known as immunoglobulins (Ig), are glycoproteins produced by B lymphocytes.
They are central to humoral immunity, the aspect of the immune system that combats pathogens in bodily fluids.
The term "Ab" is often used in the context of function (e.g., antigen neutralization), while "Ig" is used to describe structural and classification features.
Formation and Types
B cells initially express antibodies as membrane-bound receptors embedded in their plasma membrane.
Upon recognizing a specific antigen, the B cell becomes activated and differentiates into a plasma cell, which secretes soluble antibody molecules into the bloodstream.
Soluble antibodies retain the same antigen specificity but lack the transmembrane region due to alternative RNA splicing during post-transcriptional processing.
Basic Structure: Polypeptide Chains and Overall Shape
Each antibody is a quaternary protein complex consisting of four polypeptide chains:
Two identical heavy chains (larger, around 50 kilodaltons)
Two identical light chains (smaller, around 25 kilodaltons)
These four chains are linked by disulfide bonds, which provide structural integrity.
The molecule has a Y-shaped configuration, symmetrical in structure.
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