What is the permeability of the lipid bilayer of the cell membrane to proteins?

The lipid bilayer of the cell membrane is classified as impermeable to proteins due to its hydrophobic core that primarily interacts with non-polar molecules. This structure creates a barrier that prevents most polar or charged substances, including proteins, from freely passing through. Proteins are typically large, and their hydrophilic regions do not interact favorably with the hydrophobic interior of the membrane.

Instead, proteins are transported across the membrane via specific mechanisms such as facilitated diffusion or active transport involving protein channels or transporters. This selective permeability is essential for maintaining the internal environment of the cell and for the regulation of materials entering and leaving the cell.