Final answer:
Endoplasmic reticulum aminopeptidase (ERAP) is involved in antigen presentation, which is essential for the immune response.
Step-by-step explanation:
Endoplasmic reticulum aminopeptidase (ERAP) is primarily involved in c. Antigen presentation. This enzyme plays a crucial role in the immune response by trimming peptides within the endoplasmic reticulum (ER) for presentation by major histocompatibility complex (MHC) class I molecules. Protein synthesis, as referenced in options a and d, refers to the assembly of amino acids into proteins by ribosomes, typically attached to the rough endoplasmic reticulum (RER), not directly linked to the function of ERAP. Protein folding, option b, is related to the role of chaperone proteins within the ER that ensure newly synthesized proteins acquire their proper 3-dimensional shapes, which is also distinct from the antigen processing activity of ERAP. Lastly, DNA replication (option d) is a separate cellular process for duplicating the genetic material and does not involve ERAP.