Reactions in fertilisation
Capacitation- Changes required in order for a sperm to fertilise an oocyte. Takes place when travelling through the female reproductive tract and takes a few hours. Involves the removal of cholesterol and glycoproteins from the memrane above the acrosome making the membrane more fluid and permeable to Calcium ions.
The acrosome reaction- The sperm head binds to the zona pellucida (jelly coat) which triggers Calcium ions to enter the head. The outer membrane of the sperm and the acrosome membrane fuse together allowing the sperm to digest its way through the jelly coat until the sperm membrane fuses with the oocyte's plasma membrane allowing the sperm nuclei into the oocyte.
Cortical reaction- When the sperm membrane binds to the plasma membrane of the oocyte, calcium ions are released from storage sites in the oocyte. This causes vesicles in the oocyte, cortical granules, to fuse with the oocyte membrane and release their content into the space between the oocyte membrane and the jelly coat. This causes changes to the jelly coat which forms a fertilisation membrane that prevents entry of any more sperm.