What are the stages of fertilization?
What are the stages of fertilization?
The stages of fertilization can be divided into four processes: 1) sperm preparation, 2) sperm-egg recognition and binding, 3) sperm-egg fusion and 4) fusion of sperm and egg pronuclei and activation of the zygote.
Which membranes fuse first during fertilization?
During fertilization, a sperm must first fuse with the plasma membrane and then penetrate the female egg cell to fertilize it. Fusing to the egg cell usually causes little problem, whereas penetrating through the egg’s hard shell or extracellular matrix can be more difficult.
How does fertilization trigger egg activation?
Egg activation is initiated by or temporally coincident with sperm entry in many animals, therefore, the fertilized egg must first complete the second meiotic division to form the haploid maternal pronucleus then mediate fusion of the male and female pronucleus while transitioning from a meiotic cell cycle to the …
How does the change in membrane potential of the egg cell membrane prevent polyspermy?
The fast block to polyspermy. The fast block to poly-spermy is achieved by changing the electric potential of the egg plasma membrane. This membrane provides a selective barrier between the egg cytoplasm and the outside environment, and the ionic concentration of the egg differs greatly from that of its surroundings.
What is fertilization membrane?
Definition of fertilization membrane : a resistant membranous layer in eggs of many animals that forms following fertilization by the thickening and separation of the vitelline membrane from the cell surface and that prevents multiple fertilization.
Which part of sperm enters into an ovum during fertilization?
head
During fertilization, only head of spermatozoa enters egg.
What does fertilization trigger?
Fertilization ultimately causes a rise in intracellular Ca2+ that starts from the point of sperm entry and spreads in a wave-like manner across the entire egg (Gilkey et al.,1978; Eisen et al.,1984; Sardet et al.,2006). IP3 then binds to its receptor on the ER, causing Ca2+ to be released into the cytosol (Fig. 1A).
What membrane and cortical events occur during egg activation?
The interaction between sperm and egg plasma membranes leads to egg activation, which is essential for further development. Egg activation includes early events such as [Ca2+]j rise, cortical reaction (CR), resumption of the cell cycle, and later events such as pronuclear formation and DNA synthesis.
How does a fertilized egg prevent polyspermy?
An egg must be fertilized by a single sperm only. To prevent polyspermy, the zona pellucida, a structure that surrounds mammalian eggs, becomes impermeable upon fertilization, preventing the entry of further sperm. The structural changes in the zona upon fertilization are driven by the exocytosis of cortical granules.
Why is the egg membrane depolarized after fusion?
This depolarization prevents additional sperm from fusing to the egg plasma membrane. The egg plasma membrane is restored to its normal -70mV potential within minutes of fusion as the Na+ channels close, other + ions flow out of the cell, and Na+ is pumped out.
How does the egg cell membrane block polyspermy?
The fast block to polyspermy involves the opening of Na+ channels in the egg plasma membrane. Na+ flows into the egg cell, depolarizingthe membrane. This depolarization prevents additional sperm from fusing to the egg plasma membrane.
What are the steps involved in the process of fertilization?
1 Formation of the fertilization cone 2 Instant depolarization of the egg membrane 3 Release of cortical granules from the egg
What happens when sperm penetrate the egg membrane?
The head of each sperm, the acrosome, releases enzymes that begin to break down the outer, jelly-like layer of the egg’s membrane, trying to penetrate the egg. Once a single sperm has penetrated, the cell membrane of the egg changes its electrical characteristics.
