The Sperm and its Plasma Membrane
The sperm is a streamlined cell that has lost most of its cellular components to become a DNA cruise missile. The DNA is in the nucleus and is surrounded on the anterior end by the acrosome that is involved in allowing a sperm to penetrate the outer layers of the oocyte or egg. Moving past the nucleus, the head of the sperm narrows into the neck and the beginning of the tail. The first part of the tail is the middle piece which has the power house of the sperm, the mitochondria, wrapped around the central part of the tail. The mitochondria then end but the contractile elements of the tail continue on down to the end piece. The entire sperm is covered by a membrane called a plasma membrane. As with any cell, the plasma membrane of the sperm is composed of a phospholipid bilayer (2 opposing layers of lipids) as shown in the image below. Note that there is more than one type of phospholipid as indicated by the black and white polar head groups. These phospholipid move rapidly within the outer or inner layer of lipids. Within the membrane are also proteins that also move around in the membrane. The ability of these proteins to function appropriately is essential to normal physiological functions of sperm.
