Fertilisation

Question 1

What is the fertilisation?

Answer 1

o The fertilization process is the fusion of the sperm and egg to form a diploid zygote.
o This process is a complex sequence of events as depicted below in sea urchins.

Question 2

What does the sperms contact with the egg’s surface initiate?

Answer 2

The sperm’s contact with the egg’s surface initiates metabolic reactions in the egg that trigger the onset of embryonic development.

Question 3

Describe the process of how sperm enters the egg. (6)

Answer 3

1. Acrosomal reaction is stimulated by sperm contact with egg jelly.
2. Hydrolytic enzymes released from the acrosome digest the jelly coat.
3. Sperm contact causes Ca2+ influx which stimulates actin polymerization to form the acrosomal process.
4. Acrosomal process adheres to the vitelline envelope via binding proteins found in the egg membrane.
5. Sperm acrosomal process membrane fuses with egg membrane.
6. The sperm’s nucleus and centriole enter the egg after fusion occurs.

Question 4

Sperm head contains the acrosome and ______ proteins.

Answer 4

binding

Question 5

What is egg activation?

Answer 5

o Ca2+ in the cytosol increases the rate of cellular respiration and protein synthesis by the egg cell.
o The collection of these events are referred to as egg activation.

Question 6

What is required for egg activation?

Answer 6

o Proteins and mRNAs needed for activation are already present in the egg.
o The sperm nucleus fuses with the egg nucleus, and cell division begins.

Question 7

What is polyspermy?

Answer 7

Polyspermy is a fusion of additional sperm to the fertilized egg.

Question 8

How is polyspermy blocked? (4)

Answer 8

> Ca2+ also triggers the cortical reaction and cortical granules release their content via exocytosis.
Hyalin and other enzymes separate the vitelline envelope from the egg.
Cortical reactions form a fertilization envelope.
o This acts as a slow block to polyspermy.
Fusion of egg and sperm membranes triggers depolarization of the egg membrane within 1-3 seconds of entry.
o This acts as a fast block to polyspermy.

Question 9

What is hyalin?

Answer 9

> Hyalin is a sugar-rich molecule that attracts water via osmosis into the space between egg and vitelline envelope.

Question 10

o In humans, the fertilisation process is like that in Sea Urchins but much slower (__-__ hours).
o The egg uses this time to complete the _____ division.

Answer 10

12-36

meiotic

Question 11

Describe fertilisation in mammals. (5)

Answer 11

1. The sperm must travel through a layer of follicle cells that surround the egg called Corona radiata.
2. Then borrow through an extracellular matrix called Zona pellucida.
   (The fertilization process is internal.)
3. Cortical granules release enzymes that harden the zona pellucida.
4. The enzymes also strip the sperm receptors found in the egg membrane.
5. There is no known fast block polyspermy process in mammals.