What is the mechanism to avoid polyspemy in sea urchins? And why does it need to be quicker?
- After fusion the electric potential of the membrane changes, blocking other sperm
- Faster block for external fertilisation
Describe the plasma membrane binding process in sea urchins
- Under jelly coat is a plasma membrane lined with protein receptors
- As acresomal enzymes release a protrusion from sperms head develops
- Requires protein binding detected by ovum receptors
- Entry of sperm nucleus
What do sea urchins have in place of the zona pellucida and what are its properties?
- Protective jelly coat instead
- Proteins in coat have chemoattractant properties, sperm migrate towards
- Egg proteins only influence sperm from matching species and matching nuclear and mitochondrial genes
What are the 4 main stages of fertilsation in mammals?
1) Hyperactivation- vigorous motility to burrow through cells
2) Acrosome reaction at zona pellucida
3) Proteins involved in recognition process
4) Enzymes released modifying zona pellucida, blocking more sperm from entering
What is the role of the acrosome capping the sperms head?
Contains enzyme used for penetrating the coat of the ovum
What are the 5 main parts of the mammalian egg?
1) Germinal vesicle- nucleus containing DNA
2) Ooplasm- cytoplasm containing nutrients
3) Vitelline membrane
4) Zona pellucida- extracellular matrix protecting glycoprotiens, protects the egg
5) Corona radrata- layer of follicle cells
