Polyspermy is when two sperm fertilize the egg as opposed to monospermy, which is the normal fusion of one sperm nuclei with the egg nuclei creating a diploid nucleus and therefore a viable zygote. Polyspermy will result in an egg that contains more than two copies of each chromosome (for example, forming a triploid nucleus) and typically results in a zygote that is unviable.
There are two mechanisms that exist to prevent polyspermy.
The first is fast block to polyspermy. As the sperm enters, the membrane potential immediately changes within a tenth of a second. Normally, the membrane potential of the egg is -70 mV, which allows the entry of sperm. Within seconds after sperm entry, the potential becomes positive. This happens because Na+ …show more content…
The purpose is to remove the other sperm by a cortical granule reaction, specifically by raising of the vitelline envelope. There are thousands of granules beneath the cell membrane that are similar to the granules in the acrosome of sperm. They will fuse with the membrane when Ca2+ is released from the ER within the egg. This fusion will then cause an exocytosis of the granules’ contents between the cell membrane and the vitelline envelope. An enzyme, cortical granule serine protease, is included in the released contents and it will cleave the protein connections between the egg and vitelline envelope so that the envelope will be lifted off. The protease also breaks bindin receptors, which are the receptors that assist in species-specific recognition of sperm. Any sperm attached will then also be clipped off. Next there is the formation of the fertilization envelope that begins where the sperm entered and proceeds to expand around the whole egg to get rid of the excess sperm. This is formed by the binding of the cortical granuels to the vitelline envelope, which releases mucopolysaccharides causing the envelope to life from the cell membrane. This is assisted by the absorption of water. At this point, all of the excess sperm have been removed and the envelope is further stabilized to endure oceans’
There are two mechanisms that exist to prevent polyspermy.
The first is fast block to polyspermy. As the sperm enters, the membrane potential immediately changes within a tenth of a second. Normally, the membrane potential of the egg is -70 mV, which allows the entry of sperm. Within seconds after sperm entry, the potential becomes positive. This happens because Na+ …show more content…
The purpose is to remove the other sperm by a cortical granule reaction, specifically by raising of the vitelline envelope. There are thousands of granules beneath the cell membrane that are similar to the granules in the acrosome of sperm. They will fuse with the membrane when Ca2+ is released from the ER within the egg. This fusion will then cause an exocytosis of the granules’ contents between the cell membrane and the vitelline envelope. An enzyme, cortical granule serine protease, is included in the released contents and it will cleave the protein connections between the egg and vitelline envelope so that the envelope will be lifted off. The protease also breaks bindin receptors, which are the receptors that assist in species-specific recognition of sperm. Any sperm attached will then also be clipped off. Next there is the formation of the fertilization envelope that begins where the sperm entered and proceeds to expand around the whole egg to get rid of the excess sperm. This is formed by the binding of the cortical granuels to the vitelline envelope, which releases mucopolysaccharides causing the envelope to life from the cell membrane. This is assisted by the absorption of water. At this point, all of the excess sperm have been removed and the envelope is further stabilized to endure oceans’