The Zona Pellucida is a glycoprotein (ZP3) membrane surrounding the plasma membrane of an oocyte. Glyco proteins are proteins attached to the poly-peptide (short polymers of amino acids linked by peptide bonds) side chains. Simply, glycoprotein is a conjugated protein having a carbohydrate component. Plasma membrane is a biological cell membrane that separates the interior of all cells from the outside environment. Oocyte is a female reproductive cell. Zona Pellucida binds sperm and is vital for the acrosome reaction, which helps a sperm penetrate the egg cell during fertilization. Acrosome is a specialized organelle found on sperm cells. It wraps around the head of the sperm and contains enzymes designed to help the sperm penetrate the egg by breaking down the proteins in the egg&rsquo;s cell wall. In the process of acrosome reaction, the sperm cell fuses with the egg, releases the enzymes, enters the egg to complete fertilization.
An egg cell, like all animal cells, is surrounded by a plasma membrane, which protects the intracellular components and regulates the materials that go in and out of the cell. The Zona Pellucida is located just outside the egg cell’s plasma membrane and is important part of it. It is composed of 3 glyco proteins, ZP1, ZP2 and ZP3. The role of each of them is as follows.
During fertilization, the Zona Pellucida binds the sperm by sticking to proteins on its plasma membrane. When this occurs, the acrosome, an organelle on the tip of the sperm’s head, opens and releases enzymes (biological catalysts) and antigens (molecule recognized by the immune system) facilitating it to break through the touch plasma membrane of the oocyte. When a sperm experiences the acrosome reaction and breaks through the egg&rsquo;s plasma membrane, fertilization happens. After fertilization, the Zona Pellucida dies and shed in a phenomenon called “Zona hatching”. The Zona Pellucida is also essential for egg cell death in ceases when there is no fertilization.
Male infertility is sometimes due to sperm that fail to undergo the acrosome reaction. On the contrary, in some species, some release the fillings of their acrosome before reaching the egg, removing their own chance of fertilizing the egg, but increasing the motility of the other sperm. Premature acrosome reaction is most common in species in which females have many sexual partners, which results in high contest for the sperm.