01:119:115 Lecture Notes - Lecture 16: Zona Pellucida, Acrosome Reaction, Polyspermy
8 Jul 2015
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In sea urchins : egg layers/coverings (internal to external, plasma membrane, thin vitelline layer, thick glycoprotein layer (jelly coat, jelly coat can exude soluble molecules to attract sperm swimming in water a. In sea urchins : recognition event between sperm and egg triggers fusion of plasma membrane, fusion triggers depolarization of membrane, unfertilized egg is polarized (cytoplasm has negative charge relative to outside) ii. Increased aerobic respiration: maternal enzymes and proteins activated. Increased protein synthesis using maternal mrna already in cell: secondary oocyte resumes meiosis ii (had stopped @ metaphase. In sea urchins fusion occurs 20 min after sperm nucleus enters egg. In mammals, it takes several hours: first cell division marks end of fertilization and beginning of next stage of development, next step is cleavage. Cleavage stage of development is characterized by a succession of rapid cell divisions: first cell division in sea urchins occurs within 90 minutes of sperm binding to egg i.
