Final answer:
Membrane proteins differ from water-soluble proteins like phycocyanin as they feature hydrophobic domains allowing them to be embedded in the cell's lipid bilayer. They have hydrophilic regions at the ends that interact with the cell's internal and external aqueous environments.
Step-by-step explanation:
Proteins embedded in the nonpolar phospholipid bilayer of a cell membrane have unique three-dimensional structures that are suited for their environment. Unlike water-soluble proteins such as phycocyanin, membrane proteins contain hydrophobic regions that interact with the lipid tails within the bilayer. Integral membrane proteins span this bilayer, with hydrophilic domains at both ends to interact with the aqueous environments inside and outside the cell, and a hydrophobic domain to anchor them within the membrane. In contrast, peripheral proteins are attached to the membrane surface through electrostatic forces and hydrogen bonds.
This structure is essential for the function of the membrane proteins, enabling them to perform roles such as ion channels, signal transducers, or anchors. Their compatibility with the membrane's hydrophobic core is a key feature that distinguishes them from water-soluble proteins, which have more evenly distributed hydrophilic surfaces suitable for an aqueous environment. Furthermore, membrane proteins may be glycoproteins with a sugar coating that faces outside the cell, contributing to the glycocalyx involved in immune function and cellular communication.