What characteristic distinguishes integral membrane proteins from peripheral ones?

The defining characteristic of integral membrane proteins is that they penetrate the lipid bilayer of the cell membrane. This penetration allows them to span across the membrane, often consisting of one or more hydrophobic regions that interact with the fatty acid tails of the phospholipids. This positioning is crucial for the protein's functions, such as transport, acting as channels or receptors, and maintaining the structural integrity of the cell membrane.

In contrast, peripheral membrane proteins are typically bound to the exterior or interior surface of the membrane rather than embedding within the lipid bilayer. They can attach to integral proteins or directly associate with the lipid heads without penetrating into the hydrophobic core of the membrane. Understanding this difference is fundamental in the study of cell biology and membrane dynamics, as it relates to how different proteins interact with lipids and contribute to cellular functions.