Structure of antibodies is composed of
**Core Concept**
Antibodies, also known as immunoglobulins, are glycoprotein molecules that play a crucial role in the immune system by recognizing and binding to specific antigens. The structure of antibodies is composed of multiple polypeptide chains, which are highly specialized and essential for their function.
**Why the Correct Answer is Right**
The correct structure of antibodies is composed of four polypeptide chains: two heavy chains and two light chains. The heavy chains are responsible for the antibody's class and are named alpha (α), delta (δ), epsilon (ε), gamma (γ), and mu (μ). The light chains are either kappa (κ) or lambda (λ) in type. These polypeptide chains are held together by disulfide bonds and are highly specific to the antigen they bind to.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect, as antibodies are not composed of only one type of polypeptide chain.
**Option B:** Incorrect, as the correct number of polypeptide chains in an antibody is four, not three.
**Option C:** Incorrect, as while the heavy chains do contribute to the antibody's class, they are not the only component of the antibody's structure.
**Clinical Pearl / High-Yield Fact**
A key feature of antibodies is their ability to undergo class switching, where the heavy chain type is changed from one class to another while the antigen specificity remains the same. This process is essential for the immune system to adapt to different pathogens and is a critical aspect of antibody-mediated immunity.
**Correct Answer:** A. Four polypeptide chains (two heavy chains and two light chains).