Lipids and proteins are synthesized on the endoplasmic reticulum. Ribosomes are the site for protein synthesis. The ribosomes attached to the rough endoplasmic reticulum (rough ER) synthesize proteins. Those proteins are then used to form the mosaic in the phospholipid bilayer of the plasma membrane. Smooth endoplasmic reticulum (smooth ER) helps in the manufacture of lipids, which are important for cell functioning. Modifications take place in the golgi apparatus before they are sent to their destination. The golgi apparatus serves as an assembly line in which membrane proteins undergo post-translational modification. The synthesized membrane lipids and proteins must be transported by membrane-bound vesicles. The proteins and lipids made will then fuse with the cell membrane and orient themselves through hydrophobic and hydrophilic interaction within the cell.