Which are the primary molecules making up plasma membranes in cells?

Plasma membranes are made of [approximately] 50% lipids and 50% proteins.

Explanation:

In a cell, the composition of membranes varies depending on its type. The plasma membrane plays an essential role in separating the interior of the cell from the outside. They are made of [approximately] 50% lipids and 50% proteins (Cooper G., 2000) and some carbohydrates that are attached.

In these membranes, lipids are hydrophobic molecules with extremely important functions such as cell structure, biosynthesis, adhesion, growth, amongst other roles. Proteins, such as membrane receptor proteins, are also fundamental because they send and receive signals between the internal part of the cell and the external environment.