Final answer:
Partial D mutations primarily occur in the intracellular portion of the protein and in the membrane itself.
Step-by-step explanation:
Partial D mutations primarily occur in the portion of the protein that is intracellular and in the membrane itself. Proteins associated with biological membranes, called intrinsic proteins or integral proteins, are embedded in the membrane and often function as part of transport systems. A mutation in these regions can result in dysfunctional proteins, which can have significant impacts on cellular function.