Final answer:
The normal function of the PrP protein in mammals is believed to be assisting in normal synaptic development and function. So, the correct answer is option d.
Step-by-step explanation:
The normal function of the PrP protein in mammals is believed to be assisting in normal synaptic development and function. PrP protein (PrPc) is thought to bind to Ab peptides, effectively preventing their aggregation into plaques. However, when a mutant version of the protein (PrPSc) is present and misfolds, it can induce abnormal folding even in normal PrPc, leading to the formation of amyloid plaques and neurodegeneration.
So, the correct answer is option d.