The smallest immunoglobulin is IgG.
IgG (Immunoglobulin G) is the most abundant antibody isotype in the blood and extracellular fluid, and it is also the smallest. This smaller size, compared to other immunoglobulins like IgM, IgA, IgE, and IgD, allows IgG to more easily diffuse into tissues.
Here's a breakdown to illustrate why IgG is the smallest:
- Molecular Weight: IgG has a molecular weight of approximately 150 kDa. The molecular weights of other immunoglobulins are significantly higher. For example, IgM exists as a pentamer, making it much larger and heavier. IgA exists as a dimer.
- Structure: The basic structure of an immunoglobulin is a Y-shaped molecule composed of two heavy chains and two light chains. IgG is a monomer, meaning it exists as a single Y-shaped unit.
Therefore, due to its smaller molecular weight and monomeric structure, IgG is the smallest immunoglobulin.
