Question

What happens after a sperm has penetrated the extracellular coat of the egg?

Answer 1

Fertilisation:

1. When the sperm penetrates the extracellular layer of the egg, it interacts with the ovum's plasma membrane that has the tips of microvilli on the surface of the egg.
2. The adjacent microvilli quickly elongate and a group around sperms ensures it is firmly attached for it to fuse with the egg.
3. As soon as it fuses, the sperm enters the egg. First, the head enters and microvilli start to get resorbed.
4. In the sperms, fertilsin – a transmembrane protein gets bind to the surface of the sperm during the acrosomal reaction.
5. This helps the sperms to bind to the plasma membrane of the egg and can have a role in the union of the two plasma membranes.