Question

What are two functions of the protein molecules in the cell membrane?

Answer 1

1. To facilitate passive or active transportation of molecules into, or out of the cell.
2. Metabotropic receptors that facilitate biochemical cascades or other events in the cell.

An example of (1) is the voltage-gated ion channel in neurons that is generally why our neurons can communicate through action potentials.

An example of (2) is the sensory rhodopsin II receptor that effectuates the transduction of electromagnetic radiation in retinas of your eyes. I'll save you the headache of the biochemical metabolism, but if you'd like to hear about it, ask!