The property of the phospholipid bilayer that allows proteins to move laterally in the membrane is its fluidity. The bilayer behaves as a two- dimensional fluid where both lipids and proteins are free to rotate and move sideways within the plane of the membrane. This fluid nature arises because the phospholipid molecules are not covalently bonded to each other, allowing them and embedded proteins to diffuse laterally
. This fluidity is influenced by factors such as temperature, lipid composition (e.g., presence of unsaturated fatty acid chains that introduce kinks), and cholesterol content, which modulate how tightly the fatty acid chains pack together. The fluid mosaic model describes the membrane as a flexible, dynamic structure where proteins can move laterally due to the "fluid" phospholipid environment that surrounds them
. In summary, the lateral mobility of proteins in the membrane is enabled by the phospholipid bilayer's fluid, viscous nature, where phospholipids and proteins are free to move sideways within the membrane plane.
