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Activation of Egg Metabolism
Transcript of Activation of Egg Metabolism
the sperm triggers the explosive release of calcium in the egg is still something of a mystery"
Recent data suggest that the production of inositol 1,4,5-trisphosphate (IP3) is the primary mechanism for releasing calcium ions from their intracellular storage.
The IP3 pathway
The membrane phospholipid phosphatidylinositol 4,5-bisphosphate
is split by the enzyme phospholipase C
yield two active compounds:
IP3 is able to release calcium ions
into the cytoplasm by opening the calcium ion channels of the endoplasmic reticulum.
activates protein kinase C, which in turn activates a protein that exchanges sodium ions for
hydrogen ions, raising the pH of the egg
What activates the phospholipase C enzymes?
Recent Studies have suggested that PLC is activated by Protein Tyrosine Kinase
IP3-responsive calcium channels have been found in the egg endoplasmic reticulum. The IP3 formed at the site of sperm entry is thought to bind to the IP3 receptors of these channels, effecting a local release of calcium.Once released, the calcium ions can diffuse directly, or they can facilitate the release of
more calcium ions by binding to calcium-sensitive receptors located in the ER.
According to one
model, the sperm receptor
protein crosses the egg plasma membrane and has a protein tyrosine kinase activity in its cytoplasmic domain
According to a second model, the bindin receptor is linked to a protein tyrosine kinase and can activate the kinase, perhaps as a consequence of receptor crosslinking by
Third possibility is that the activation of the IP3 pathway is caused not by the binding of sperm and egg, but by the fusion of the sperm and egg
What are the 2 products obtained by cleavage of PIP2 by PLC?
How does IP3 release calcium ions?
Where are the intracellular calcium ions sequestered?
Exchange of Na+/H+ is switched ON by which chemical?
What would happen if I inhibited the IP3 synthesis?
1. IP3 and DAG
2.Opens Ca+ channels in ER
5.Calcium Release Prevented