Final answer:
Complement proteins are encoded by the genes located in the MHC class III complex, with MHC class I molecules playing a central role in the immune system's defense strategy.
Step-by-step explanation:
Complement proteins are encoded by genes in the MHC class III gene complex. The correct answer to the question is option C. III.
MHC class I molecules are found on the surface of all nucleated cells and are involved in presenting abnormal or non-self-antigens to T cells. These molecules are composed of a longer α protein chain coupled with a smaller β2 microglobulin protein, and only the α chain spans the cytoplasmic membrane.
The function of these MHC class I molecules is crucial for the immune system's defense strategy, as they help the body to recognize and deal with infected or cancerous cells by providing a template into which antigens can be loaded for recognition by lymphocytes.