Final answer:
TAP genes transport peptides into the ER for binding to MHC-I, essential for antigen presentation to T cells.
Step-by-step explanation:
The products of the transporter associated with antigen processing (TAP) genes are involved in the immunological process of antigen presentation. Their specific function is to transport peptides from the cytosol into the endoplasmic reticulum (ER). Once inside the ER, these peptides bind to Major Histocompatibility Complex class I (MHC-I) molecules. Following this association, the peptide-MHC-I complex is then transported to the surface of the cell via a transport vesicle. The correct answer to the student's question is, therefore, D. transport peptides into the endoplasmic reticulum for binding to MHC-I.