Final answer:
The heavy chain in an immunoglobulin molecule has additional constant domains compared to the light chain. These extra constant domains are structured into loop-shaped zones created by intrachain disulfide bonds, adding to the antibody's complexity.
Step-by-step explanation:
The extra sequence found in the heavy chain of an immunoglobulin that is not present in the light chain can be described as additional constant domain regions. The heavy chains contain one variable domain (VH) and either three or four constant domains (CH¹, CH², CH³ and C´) depending on the antibody class. In contrast, light chains contain just one variable domain (V¹) and one constant domain (C¹). Specifically, the constant region of heavy chains includes three to four independent domains, referred to as 'domains,' each of which is created by intrachain disulfide bonds and folded into recognizable loop shapes. These additional domains in heavy chains contribute to the structural complexity and functional versatility of antibodies.