Question

Normal fertilization requires changes in the membrane organization of both sperm and oocyte and penetration of the oocyte by a single spermatozoon.

a. What physical, cellular and biochemical molecular processes are necessary for the succesful passage of a spem from the outermost portion of the cumulus oophorus to the oocyte membrane?

b. How does the human sperm nucleus move in the cytoplasm and why does it facilitate the juxtaposition of the material and paternal pronuclei?

Answer 1

Ans a) In order for the sperm to pass through the outermost portion of the cumulus oophorus to the oocyte membrane, there are number of physical, cellular and biochemical molecular processes involved. After one minute of the ejagulation the sperm undergoes coagulation which temporarily restricts its movement out of the seminal clot. The mature ovum consists of number of surrounding layers that penetrates by the spermatozoa for normal process of fertilization. The spermatozoa have a cap like structure called acrosome which helps with membrane fusion and sperm entry into the ovum. The acrosome reaction is initiated as the spermatozoa arrives at the ovum. The outermost covering of the ovum which is called cumulus oophorus is broken down by hyaluronidase which is present in the plasma membrane of the spermatozoa. The sperm binds to zona pellucid and proacrosin zymogen converts the zymogen into acrosin leading to breakdown of the zona pellucid. This leads to the removal of the spermatozoa plasma membrane and acrosomal membrane. After it moves through the zona pellucid, sperm attached to the perivitelline space and attach to the ovum cell membrane. This leads to fusion of the sperm and ovum plasma membrane allowing its entry into ovum for fertilization.