The cell membrane is primarily made up of a phospholipid bilayer along with proteins and glycolipids. This bilayer arrangement forms a semi-permeable barrier that controls the movement of substances in and out of the cell. In eukaryotic cells, sterols such as cholesterol are also present in the cell membrane, contributing to membrane fluidity and stability. The nuclear membrane, also called the nuclear envelope, consists of two lipid bilayer membranes—an inner and an outer membrane—that surround the nucleus. It is made of phospholipid bilayers like the cell membrane but has an additional layer since it is a double membrane. The nuclear membrane contains nuclear pores that regulate the passage of molecules such as proteins and RNA in and out of the nucleus. A protein mesh called the nuclear lamina underlies the inner membrane, providing structural support to the nucleus. In summary:
- Cell membrane: a single phospholipid bilayer with proteins, glycolipids, and sterols.
- Nuclear membrane: two phospholipid bilayers (inner and outer) with nuclear pores and nuclear lamina proteins for support.
