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acrosome reaction
- 1. Topic Prepared by Rajamoni saikia M.Sc 1st semester zoology
- 2. It is only within the past 135 year that the sperms roll in fertilization has been known . Anton van leeuwenhoek , the dutch microscopist who co-discovered sperm in the 1670 s, Each sperm cell consist of a haploid nucleolus . In front of this compressed haploid nucleus lies the acrosomal vesicle , or acrosome . The acrosome is derive from the cells Golgi apparatus and contain enzymes that digest proteins and complex sugars . Acrosome +nucleus = sperm head .
- 3. A second interaction between sperm and egg jelly result in the acrosome reaction . In a acrosome reaction in initiated by contact of the sperm with the egg jelly. Exocytosis occur in acrosomal vesicle . Proteolytic enzyme and proteasomes that digest a path through the jelly coat to the egg surface . Sulphate containing polysaccharide bind to the specific receptor located on the sperm cell membrane directly above the acrosomal vesicle . Thus acrosome reaction constitute a barrier to interspecific fertilisation .
- 4. Figure 47.3-1 Basal body (centriole) Sperm head Acrosome Jelly coat Sperm-binding receptors Vitelline layer Egg plasma membrane
- 5. Figure 47.3-2 Basal body (centriole) Sperm head Acrosome Jelly coat Sperm-binding receptors Hydrolytic enzymes Vitelline layer Egg plasma membrane
- 6. Figure 47.3-3 Basal body (centriole) Sperm nucleus Sperm head Acrosome Jelly coat Sperm-binding receptors Hydrolytic enzymes Vitelline layer Egg plasma membrane Actin filament Acrosomal process
- 7. Figure 47.3-4 Basal body (centriole) Sperm plasma membrane Sperm nucleus Sperm head Acrosome Jelly coat Sperm-binding receptors Fused plasma membranes Hydrolytic enzymes Vitelline layer Egg plasma membrane Actin filament Acrosomal process
- 8. Figure 47.3-5 Basal body (centriole) Sperm plasma membrane Sperm nucleus Sperm head Acrosome Jelly coat Sperm-binding receptors Fertilization envelope Cortical granule Fused plasma membranes Hydrolytic enzymes Vitelline layer Egg plasma membrane Perivitelline space EGG CYTOPLASM Actin filament Acrosomal process
- 9. Acrosome reaction Acrosome reaction is initiated by repeating polymer of fucose sulphate . When this sulphate binds to its receptor on the sperm the receptor activates three sperm proteins . 1) A calcium transport channel that allows ca2+ to enter the sperm heat . 2) A sodium Na/H exchanger that pumps sodium ion into the sperm as it pumps hydrogen ion out . 3) A phpospholipase enzyme that makes another second messenger the phospholipid inositol trisphosphate (ip3) . Ip3 able to release calcium from inside the sperm . The elevated calcium level in a relatively basic cytoplasm triggers the fusion of acrosomal membrane with the adjacent sperm cell membrane . Releasing enzyme that can lyse a path through the egg jelly to the vitelline envelop.
- 10. It extend of the acrosomal process . This protrusion arises through the polymerization of globular actin molecules into actin filament. The influx of calcium is thought to inactivate the protein RhoB in the acrosomal region and mid piece of sea uracin sperm. This GTP binding protein helps to active in polymrising actin to make the acrosomal processes.
- 11. The acrosome reaction allow the sperm by exocytosis release of acrosomal enzyme to penetrate the zona pellucida of the egg. The species specific zona pellucida protein that serve as a sperm receptor also stimulates a seri9es of event that lead to fusion between the plasma membrane and outré acrosomal membrane.