The structure of a typical immunoglobulin consists of how many light and heavy chains?

• A. 2 Light and 2 Heavy
• B. 4L and 2H chains
• C. 4L and 4H chains
• D. 2L and 4H chains

Answer: (A)

Immunoglobulins are built from two identical light chains and two identical heavy chains, linked together to form a Y-shaped molecule. Each arm of the Y is made from one light chain paired with one heavy chain, creating two antigen-binding fragments (Fab). The stem, called the Fc region, comes from the constant parts of the two heavy chains and handles effector functions. This two-light, two-heavy arrangement is why antibodies have two binding sites and a stable core structure. The other options would not yield the proper Fab–Fc architecture, as they imply the wrong total number of chains.