What type of proteins do not penetrate the cell membrane?

Peripheral proteins are characterized by their location on the cell membrane's surface rather than being embedded within it. They typically interact with the membrane's lipid bilayer or with integral proteins but do not extend through the membrane itself. This distinction is important in understanding cellular functioning and how different types of proteins contribute to the cell's architecture and signaling pathways.

Transmembrane proteins and integral proteins are embedded within the lipid bilayer, facilitating a wide range of functions including acting as channels, receptors, and transporters. Structural proteins can also be integral to the function and shape of the membrane, often forming the cytoskeleton's framework. Peripheral proteins, by contrast, play roles in signaling, maintaining the cell's shape, and facilitating connections with other cells, but they do not penetrate the membrane barrier. This specificity allows them to function differently from the other protein types listed.