Which protein helps in species specific recognisition of sperm and egg?
Answers
Once the sea urchin sperm has penetrated the egg jelly, the acrosomal process of the sperm contacts the surface of the egg (Figure 7.14A). A major species-specific recognition step occurs at this point. The acrosomal protein mediating this recognition is called bindin
The egg jelly causesthe acrosomal reaction to occur, allowing the acrosomal process to form and release proteolytic enzymes.
The sperm adheres to the vitelline envelope and lyses a hole in it.
The sperm adheres to the egg plasma membrane and fuses with it. The sperm pronucleus can now enter the egg cytoplasm.
Mammalian fertilization is internal.
The contents of the female reproductive tract capacitate, attract, and activate the sperm.
The acrosome-intact sperm binds to the zona pellucida, which constitutes a thicker envelope than that of sea urchins.
The acrosomal reaction occurs on the zona pellucida.
The sperm digests a hole in the zona pellucida.
The sperm adheres to the egg, and their plasma membranes fuse
1.
The chemoattraction of the sperm to the egg by soluble molecules secreted by the egg
2.
The exocytosis of the acrosomal vesicle to release its enzymes
3.
The binding of the sperm to the extracellular envelope (vitelline layer or zona pellucida) of the egg
4.
The passing of the sperm through this extracellular envelope
5.
Fusion of egg and sperm cell plasma membranes
Sometimes steps 2 and 3 are reversed (as in mammalian fertilization) and the sperm binds to the egg before releasing the contents of the acrosome. After these five steps are accomplished, the haploid sperm and egg nuclei can meet, and the reactions that initiate development can begin.
In many species, the meeting of sperm and egg is not a simple matter. Many marine organisms release their gametes into the environment. That environment may be as small as a tide pool or as large as an ocean. Moreover, it is shared with other species that may shed their sex cells at the same time. These organisms are faced with two problems: How can sperm and eggs meet in such a dilute concentration, and how can sperm be prevented from trying to fertilize eggs of another species? Two major mechanisms have evolved to solve these problems: species-specific attraction of sperm and species-specific sperm activation.