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# Long description

The diagram shows the double layer of phospholipid molecules: the polar head of each phospholipid molecule is shown as a blue sphere and the two hydrophobic or non-polar tails attached to the head are shown as zig-zag yellow ribbons. The tails in each layer are oriented in parallel and are facing, but not touching, the tails of the opposing layer in the bilayer structure. Interspersed between the phospholipid molecules are so-called integral protein molecules (shown here in red) which span the width of the membrane and provide aqueous channels or pores in the membrane. Other protein molecules, the peripheral membrane proteins, are attached to the cytosolic surface of the membrane. Some of the proteins and lipids at the extracellular surface of the membrane have short, sometimes branched sugar chains attached; these are called glycoproteins and glycolipids, respectively.