Final answer:
Immunoglobulin domains are primarily composed of anti-parallel β-pleated sheets that are stabilized by hydrophobic interactions. These structures are crucial for the antigen-binding ability of the antibody and are a result of the evolutionary conservation of certain amino acid sequences forming these domains.
Step-by-step explanation:
Immunoglobulin domains consist of anti-parallel β-pleated sheets folded and stabilized by hydrophobic interactions (option C). Immunoglobulin molecules are made up of two identical light chains and two identical heavy chains, forming a tetramer (L₂H₂) connected by interchain disulfide bonds. Each chain can be divided into domains, with light chains having two domains (one in the variable region and one in the constant region) and heavy chains having four domains. The domains are formed by loops of approximately 60 amino acids connected by intrachain disulfide bonds.
These domains show homology in their amino acid sequences, which is a result of the evolutionary process. The secondary structures of proteins, α-helix and β-pleated sheet, are essential for the stability and function of proteins. In the case of immunoglobulin domains, the structure is primarily composed of β-pleated sheets, which are stabilized by hydrogen bonds between the backbone's carbonyl and amine groups. This structural motif is crucial for the antibody's ability to bind specific epitopes on antigens, a key aspect of the immune response.