This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Physiology
The immunoglobulin lacking hinge region is 
Select and explain. 
A. Ig A, B. Ig G, C. Ig D, D. Ig E
D: Ig E
Answer: D: Ig E 
Explanation: Hinges contribute to flexibility of immunoglobulin molecules. They contain cysteine and proline. Cysteine provides interchain linkage.Proline cannot be incorporated into secondary structure of immunoglobulin molecules. The immunoglobulins Ig M & Ig E lack the hinge region. They have an extra domain in the constant region-Ch4