What happens in the cortical reaction?
The cortical reaction, also known as the zona reaction, occurs when a sperm unites with the egg’s plasma membrane, altering the zona pellucida which prevents other sperm from binding to and entering the egg.
What do cortical granules do in sea urchin fertilization?
Cortical granules are secretory vesicles poised at the cortex of an egg that, upon stimulation by sperm contact at fertilization, secrete their contents. These contents modify the extracellular environment and block additional sperm from reaching the egg.
What is the function of the cortical reaction?
Abstract. The cortical reaction is a calcium-dependent exocytotic process in which the content of secretory granules is released into the perivitellin space immediately after fertilization, which serves to prevent polyspermic fertilization.
What is the cortical reaction and where does it occur?
Fusion of the plasma membranes of the sperm and oocyte triggers the cortical reaction, which prevents other sperm from entering the oocyte. The union of oocyte and sperm occurs in the ampulla of the oviduct and marks the initiation of prenatal development.
Why can only one sperm enter an egg?
The egg and sperm each contain one set of chromosomes. To ensure that the offspring has only one complete diploid set of chromosomes, only one sperm must fuse with one egg. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum.
What is released in the cortical granules?
The fertilization envelope is formed by the lifting of the vitelline envelope away from the egg plasma membrane. The cortical granules contain enzymes that aid in the detachment of the vitelline envelope, as well as other components that aid the osmotic swelling of the fertilization envelope away from the egg.
What is cortical reaction and why is it important?
The cortical reaction is a process initiated during fertilization that prevents polyspermy, the fusion of multiple sperm with one egg.
What does cortical granules contain?
The cortical granules contain enzymes that aid in the detachment of the vitelline envelope, as well as other components that aid the osmotic swelling of the fertilization envelope away from the egg.
What is an oocyte cortical reaction?
The cortical reaction is a process through which cortical granules from the oocyte are released preventing polyspermy. The fast block of polyspermy immediately prevents additional sperm getting attached to the oocyte.
What is difference between acrosome reaction and cortical reaction?
Acrosome Reaction: A regulated exocytotic event in which an apical vesicle in the sperm head fuses with the sperm plasma membrane. Cortical Reaction: A regulated exocytosis in which apically localized vesicles (cortical granules) in the egg fuse with plasma membrane after fertilization.
What is a acrosome?
The acrosome is a special kind of organelle with a cap-like structure that covers the anterior portion of the head of the spermatozoon. The acrosome is derived from the Golgi apparatus and contains digestive enzymes.
What is Fertilisation Ncert?
The fusion of haploid male gamete, sperm and haploid female gamete, ovum is called fertilization. The haploid nucleus of the sperm and ovum fuse together to form a zygote which develops into new individual.
Where are the cortical granules in a sea urchin egg?
The sea urchin egg contains about 15,000 cortical granules lying in a layer just beneath the plasma membrane. Each granule have a diameter of about 1 µm. The free calcium ions initiate the cortical granules to move to the inner surface of the plasma membrane and to fuse with it.
How does fertilization take place in a sea urchin?
Four important events of fertilization in the sea urchin are: 1) the acrosome reaction of the sperm, 2) sperm-egg fusion, 3) the cortical reaction of the egg, and 4) the formation of the fertilization coat. The acrosome reaction is triggered by contact of the sperm with the jelly coat, a complex extracellular matrix surrounding the egg.
How does a sea urchin avoid polyspermy?
Sea urchin has evolved two blocks to avoid polyspermy. The fast block to polyspermy is accomplished by a temporary electrical change in the egg plasma membrane. This is followed by a slower, more complex but permanent block called the slow block to polyspermy (Fig. 5.22).
What kind of chemotaxin does a sea urchin have?
One such chemotaxin is a 14-amino acid peptide called resect, has been isolated from the egg jelly of a sea urchin Arbacia punctulata. Resact diffuses readily in sea-water.