Question

dracribe the acrosomql reaction. be sure to identify all of the structure and/ ot molecules involved, ans include the cytokeletal protein that the sperm uses ti attach itself to the egg.

Answer 1

The zonal pellucide of most mammalian egg is composed of mainly three glycoproteins - ZP1 , ZP2 and ZP3 .This glycoproteins matrix binds the sperm and once the sperm is bound initiates the acrosome reaction.The ZP3 induces sperm to undergo acrosome reaction in which the contents of the acrosome are released by exocytosis.The exocytosis of the acrosome vesicle releases a variety proteases that lyse the zonal pellucida.These enzymes creates a hole through which sperm can travel towards egg.The acrosome reaction is mediated by intracellular calcium increase.The plasma membrane channels involved in calcium entry are operated by a plasma membrane depolarization and protein phosphorylation mediated by protein kinase C and tyrosine kinase protein.Part of the calcium increase could also be due to intracellular store release through IP3 and cAMP gates channel.Besides adenylate cyclese and phospholipase C activation intracellular calcium increase also stimulates Phospholipase A2 activity and actin polymerization leading to membrane fusion.

Acrosome reaction alters the sperm surface so that it can bind to and fuse with plasma membrane of the egg.In mammals the sperm contacts the egg not at its tip but on side of the head.The molecular mechanism is not known.Two proteins have been shown to be required for the fusion.One is sperm specific transmembrane protein of the immunoglobulin super family called Izumo.It becomes exposed during acrosome reaction.The protein present on egg surface is CD9 protein.