Question

Which of the following is not true about antibodies?

• A. Antibodies have multiple antigen binding sites.
• B. Antibodies are built from equal number of large (heavy) and small (light) chains.
• C. The class of antibody molecule is determined solely by its heavy chain.
• D. Antibodies are secreted and function away from the cell. They are not bound to the cell membrane.

Answer 1

The correct option is D

Antibodies are secreted and function away from the cell. They are not bound to the cell membrane.

All antibody units are made up of two identical heavy chains and two identical light chains. The Y shaped antibody unit has an antigen binding site at the end of each arm of the Y, so all antibodies have at least two antigen binding sites. There are nine alternative genes coding for the constant region of the heavy chain. The class of antibody produced is determined by the one that is expressed.
Non-activated B-cells carry an antibody attached to their cell membrane. Additionally IgE are attached to the membranes of the mast cells. Therefore they are not always secreted.