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Receptors for sperm binding in mammals are present on:
During mammalian fertilization, capacitated sperm binds specifically to species-specific glycoprotein receptors (ZP3) on the Zona Pellucida. This binding induces the acrosome reaction and blocks polyspermy! Match Option (4) in 5 seconds!
At the time of ovulation and subsequent fertilization in the ampulla of the fallopian tube, the secondary oocyte is surrounded by three structural barriers: 1. Corona radiata: An outer cellular coat composed of follicular granulosa cells cemented by hyaluronic acid. 2. Zona pellucida: A thick, non-cellular, transparent glycoprotein coat secreted by the oocyte and surrounding follicle cells. 3. Perivitelline space: Fluid-filled space separating the zona pellucida from the underlying vitelline membrane (plasma membrane/oolemma).
The zona pellucida is composed of four primary glycoproteins: ZP1, ZP2, ZP3, and ZP4. ZP3 functions as the primary sperm receptor: - Proteins on the sperm head plasma membrane specifically bind ZP3. - This binding triggers an influx of into the sperm, initiating the acrosome reaction. - Hydrolytic enzymes (acrosin, hyaluronidase) digest a path through the zona pellucida. - Upon entry of the first sperm, cortical granules release enzymes into the perivitelline space that alter the zona pellucida (zona reaction or cortical reaction), destroying remaining ZP3 receptors to permanently block polyspermy.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
Incorrect. The corona radiata is dispersed enzymatically by sperm hyaluronidase; it does not contain specific sperm docking receptors.
Incorrect. The vitelline membrane (oolemma) fuses with the sperm membrane only after the sperm has already bound and penetrated the zona pellucida.
Incorrect. The perivitelline space is a fluid-filled cavity, not a membrane receptor surface.
Correct. The zona pellucida contains the definitive ZP3 glycoprotein receptors responsible for species-specific sperm binding and induction of the acrosome reaction.
Students frequently assume sperm binds first to the corona radiata because it is encountered first. However, the sperm merely pushes through corona radiata cells via hyaluronidase, and true molecular receptor binding occurs on the zona pellucida.
"Sperm binding to glycoprotein receptors on the zona pellucida induces the acrosome reaction and prevents entry of multiple sperms."
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