Human Immunoglobulin G is the main antibody in the serum.  Notice how the dimer is perfectly symmetrical about a single axis of rotation. The Y-shaped molecule consists of four polypeptide chains, two identical heavy chains and two identical light chains.

The heavy chain (blue)   is about twice as long as the light chain (yellow) .

Each L chain is linked to an H chain by a disulfide bond. The resultant Y-shaped molecule has two identical antigen binding sites.

  Click here to see the two LH dimers. 

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