Anonymous
Jan 6
Formation of fertilization cone in egg? And prevention of polyspermy?
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Jan 6
The formation of a fertilization cone in the egg is a process that occurs in some species, particularly in aquatic organisms. It is a mechanism that helps guide the sperm towards the egg for successful fertilization.
During fertilization, when a sperm approaches the egg, it triggers a series of changes in the egg's membrane. These changes include the formation of a fertilization cone, also known as the fertilization cone or the attraction cone. The fertilization cone is a protrusion that extends from the egg's surface towards the approaching sperm.
The formation of the fertilization cone is facilitated by the release of calcium ions from the egg's cytoplasm. This calcium influx causes the actin filaments in the egg's cytoskeleton to rearrange, leading to the formation of the cone. The fertilization cone acts as a physical guide, directing the sperm towards the egg's micropyle, which is a small opening in the egg's membrane.
Prevention of polyspermy, or the entry of multiple sperm into the egg, is crucial for successful fertilization. If polyspermy occurs, it can disrupt the normal development of the embryo. To prevent polyspermy, eggs have evolved various mechanisms.
One common mechanism is the fast block to polyspermy, which is a rapid electrical change in the egg's membrane potential upon fertilization. This change is triggered by the fusion of the sperm with the egg, and it depolarizes the egg's membrane, making it temporarily unresponsive to other sperm. This fast block occurs within seconds of fertilization and helps prevent additional sperm from binding to the egg.
Another mechanism is the slow block to polyspermy, also known as the cortical reaction. After the fast block, the slow block is initiated to reinforce the prevention of polyspermy. The cortical reaction involves the release of cortical granules from the egg's cytoplasm into the perivitelline space, which is the space between the egg's plasma membrane and the vitelline envelope. The cortical granules release their contents, which include enzymes and other molecules, causing the vitelline envelope to harden or thicken. This hardening or thickening of the envelope creates a physical barrier that prevents additional sperm from binding to the egg.
Overall, the formation of a fertilization cone helps guide the sperm towards the egg, while the fast and slow blocks to polyspermy prevent multiple sperm from fertilizing the egg, ensuring successful fertilization and normal embryo development.
During fertilization, when a sperm approaches the egg, it triggers a series of changes in the egg's membrane. These changes include the formation of a fertilization cone, also known as the fertilization cone or the attraction cone. The fertilization cone is a protrusion that extends from the egg's surface towards the approaching sperm.
The formation of the fertilization cone is facilitated by the release of calcium ions from the egg's cytoplasm. This calcium influx causes the actin filaments in the egg's cytoskeleton to rearrange, leading to the formation of the cone. The fertilization cone acts as a physical guide, directing the sperm towards the egg's micropyle, which is a small opening in the egg's membrane.
Prevention of polyspermy, or the entry of multiple sperm into the egg, is crucial for successful fertilization. If polyspermy occurs, it can disrupt the normal development of the embryo. To prevent polyspermy, eggs have evolved various mechanisms.
One common mechanism is the fast block to polyspermy, which is a rapid electrical change in the egg's membrane potential upon fertilization. This change is triggered by the fusion of the sperm with the egg, and it depolarizes the egg's membrane, making it temporarily unresponsive to other sperm. This fast block occurs within seconds of fertilization and helps prevent additional sperm from binding to the egg.
Another mechanism is the slow block to polyspermy, also known as the cortical reaction. After the fast block, the slow block is initiated to reinforce the prevention of polyspermy. The cortical reaction involves the release of cortical granules from the egg's cytoplasm into the perivitelline space, which is the space between the egg's plasma membrane and the vitelline envelope. The cortical granules release their contents, which include enzymes and other molecules, causing the vitelline envelope to harden or thicken. This hardening or thickening of the envelope creates a physical barrier that prevents additional sperm from binding to the egg.
Overall, the formation of a fertilization cone helps guide the sperm towards the egg, while the fast and slow blocks to polyspermy prevent multiple sperm from fertilizing the egg, ensuring successful fertilization and normal embryo development.
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