How are membrane-bound immunoglobulin molecules anchored?

Membrane-bound immunoglobulin molecules, commonly found on B lymphocytes, are anchored in the membrane by a hydrophobic sequence of about 26 amino acid residues. This hydrophobic region, often referred to as a transmembrane domain, interacts with the lipid bilayer of the cell membrane, allowing the immunoglobulin to remain embedded and functional as a receptor.

This anchoring mechanism is crucial for the immunoglobulins to participate in cell signaling and immune responses; they serve as receptors that can bind antigens and activate the B cell. The transmembrane domain's length and hydrophobic properties are specifically designed to facilitate this interaction with the cellular membrane.

Other options like a disulfide bond, carbohydrate chain, or lipid anchor do not play a role in the anchoring of membrane-bound immunoglobulins. Disulfide bonds are primarily involved in stabilizing protein structures, carbohydrate chains may be associated with glycosylation but do not anchor the molecule to the membrane, and while lipid anchors are used in some proteins, they are not the mechanism employed by immunoglobulins for membrane attachment.