Final answer:
The phenomenon described is best described as cellular differentiation. Cellular differentiation is the process by which cells become specialized to perform specific functions.
Step-by-step explanation:
The phenomenon described in the question is best described as cellular differentiation. Cellular differentiation is the process by which cells become specialized in order to perform specific functions. In this case, the brain cell produces proteins necessary for the assembly and release of synaptic vesicles at synapses, while the liver cell does not produce these proteins.