AR3

Question 1

What is the mechanism to avoid polyspemy in sea urchins? And why does it need to be quicker?

Answer 1

• After fusion the electric potential of the membrane changes, blocking other sperm
• Faster block for external fertilisation

Question 2

Describe the plasma membrane binding process in sea urchins

Answer 2

• 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

Question 3

What do sea urchins have in place of the zona pellucida and what are its properties?

Answer 3

• 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

Question 4

What are the 4 main stages of fertilsation in mammals?

Answer 4

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

Question 5

What is the role of the acrosome capping the sperms head?

Answer 5

Contains enzyme used for penetrating the coat of the ovum

Question 6

What are the 5 main parts of the mammalian egg?

Answer 6

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