Proteins, lipids and carbohydrates.
PROTEINS have the following functions:
- structural function (serving as the membrane exoskeleton together with lipids)
- transport function (they help transporting elements from one side of the membrane to the other)
- signalling function (depending on which proteins the cell has in its membrane it is perceived differently by other cells and microorganisms).
LIPIDS have a structural function : both phospholipids and cholesterol, constituting the roof the membrane and regulating how fluid it is.
CARBOHYDRATES that are attatched to both lipids and proteins have signalling function , and they are only on the external side of the membrane



