01:119:116 Lecture Notes - Lecture 16: Zona Pellucida, Cortical Reaction, Polyspermy
22 Apr 2016
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Document Summary
Sperm dissolves protective layers to reach plasma membrane. Sperm surface molecules binds to receptors on egg surface (same species) Surface of egg changes to prevent polyspermy (so only one sperm enters) Egg coverings: internal to external (plasma membrane, vitelline layer, jelly coat) Eternal fertilizers sperm released in h2o; jelly coat of eggs exclude chemicals in h2o attract sperm (chemotaxis) Steps of fertilization (sperm entry: contact: sperm contact with egg jelly coat; triggers exocytosis of sperm"s acrosome, acrosomal reaction: acrosome releases hydrolytic enzymes that partially digest jelly coat. Formation of acrosomal process: made of actin filaments. 1 to 3 seconds after sperm fuse: ion channels in egg pm open, na+ diffuse and enter egg, egg is depolarized. Cortical reaction: vitelline layers lift away from egg and hardens forms fertilization envelope (protective layer; prevent entry of additional sperm) Enzymes clip off and release external portion or remaining receptors with other attached sperm (requires one minute complete block): irreversible and permanent.
