Polyspermy

Question 1

What is polyspermy?

Answer 1

The fertilisation of an egg by more than one sperm

Question 2

What are the consequences of polyspermy?

Answer 2

Chromosomal issues, high embryonic mortality

Question 3

What is fast-block to polyspermy?

Answer 3

An electrical barrier that occurs soon after fertilisation

Question 4

What is the process of fast-block to polyspermy?

Answer 4

1. RMP of egg: -70mV
2. Sperm binding triggers Na+ channels to open
3. Na+ ions flow into egg due to concentration gradient
4. Membrane depolarises to 20mV
5. Positive MP blocks additional sperm

Question 5

What is the process of fast-block to polyspermy?

Answer 5

1. RMP of egg: -70mV
2. Sperm binding triggers sodium channels to open
3. Na+ ions flow into the egg due to concentration gradient
4. Membrane depolarises to 20mV
5. Positive MP blocks additional sperm

Question 6

What is slow block to polyspermy?

Answer 6

Long-lasting barrier that occurs after fertilisation in the eggs of sexually reproducing organisms

Question 7

How is the cortical reaction triggered?

Answer 7

When the sperm acromsomal tubule binds with the eggs membrane

Question 8

What is the cortical reaction?

Answer 8

This is when the cortical granules fuse with the egg membrane, releasing compounds: Serine proteases, Mucopolysacchrides, peroxidases, hyaline proteins

Question 9

What is the role of serine proteases?

Answer 9

• Seperate the vitelline membrane from the plasma membrane = perivitelline membrane = elevated
• destroy glycoprotein sperm receptor sites

Question 10

What is the role of Mucopolysacchrides?

Answer 10

Use osmotic pressure to draw water into the perivitelline space

Question 11

What is the role of peroxidases?

Answer 11

Harden the membrane = fertilisation envelope

Question 12

What is the role of hyaline proteins?

Answer 12

Form a protective layer underneath the fertilisation envelope

Question 13

Why is Ca2+ important in the slow-block process?

Answer 13

• Ca2+ concentration increases when the sperm binds to the egg, opening ion channels
• Ca2+ regulates the process
• triggers the cortical reaction
• self-propagating wave of calcium release
• Advances cortical granule exocytosis around the eggs surface

Question 14

What are the differences in the two blocking mechanisms?

Answer 14

Fast block: Rapid but transient protection
Slow block: Multi-layered, long-lasting defense
- Both mechanisms complement each other to prevent polyspermy