Final answer:
An immunoglobulin molecule has two heavy chains and two light chains. Light chains are kappa or lambda but not both, while heavy chains determine the class of the immunoglobulin (IgG, IgA, IgM, IgE, IgD). The pairing of these chains forms a Y-shaped structure.
Step-by-step explanation:
An immunoglobulin (Ig), also known as an antibody, has a specific structure comprising four polypeptide chains: it contains two identical heavy chains and two identical light chains. The arrangement of these chains forms a Y-shaped structure. Each light chain is made up of one variable domain (VL) and one constant domain (CL), with a total of 214 amino acids. The heavy chains each contain one variable domain (VH) and three or four constant domains (CH1, CH2, CH3, and possibly CH4), with each heavy chain consisting of 446 amino acids.
The light chains can be of two types, kappa (k) or lambda (λ), and all immunoglobulin molecules have light chains of just one type, either kappa or lambda, but not both. In humans, kappa chains are more common than lambda, with a ratio of approximately 2:1. Conversely, the heavy chains come in five different types (γ, α, μ, ε, and δ), which determine the immunoglobulin class (IgG, IgA, IgM, IgE, IgD), and the presence of a specific heavy chain allows for binding with light chains of any type, as long as they are both the same within a given antibody molecule. Furthermore, multimeric IgM and IgA have an additional joining (J) chain that stabilizes the structure.