Cell membrane. Computer artwork of the plasma membrane of a cell showing sugars (red) protruding from the outer surface. The sugars are linked to membrane proteins and lipids forming glycoprotein and glycolipid groups. These surface sugars act as receptors and are responsible for recognising and binding molecules, for example hormones or toxins. The plasma membrane itself is formed of a lipid bilayer (green) with integral transmembrane proteins (purple). Inside the cell is a stack of Golgi apparatus (lower right) producing lysosomes (blue spheres). Lysosomes are vesicles containing digestive enzymes.