The zona pellucida is a glycoprotein coat surrounding the secondary oocyte. Which glycoprotein component of the zona pellucida binds specifically to the sperm acrosomal receptors and initiates the acrosome reaction?
- A ZP3 (zona protein 3) ✓
- B ZP1
- C ZP2
- D ZP4
Correct answer: A. ZP3 (zona protein 3)
Explanation
The zona pellucida consists of three glycoproteins: ZP1 (structural, cross-links ZP2 and ZP3 fibrils), ZP2, and ZP3. ZP3 is the primary sperm receptor — it binds to the sperm head surface (to proteins on the plasma membrane overlying the acrosome) and triggers the acrosome reaction (exocytosis of acrosomal enzymes including acrosin and hyaluronidase), which digests the zona. After fertilization, ZP2 is cleaved by cortical granule enzymes to harden the zona pellucida and prevent polyspermy (zona reaction). This is key embryology for NEET PG.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.