Week 2 - Fertilisation

Question 1

Oocyte Development Summarised

Answer 1

Question 2

When should sex occur for successful fertilisation?

Answer 2

between 3 days before and 1 day after ovulation

Question 3

How many days does it take beating cilia to move egg along the fallopian tube

Answer 3

4 days for egg to reach the uterus

Question 4

What is sperm capacitation?

Answer 4

• replaces the wavelike beats of a sperm’s tail with a more whiplike action that propels the sperm forward in strong surges
• causes sperm’s plasma membrane to become fragile so hydrolytic enzymes in acrosomes can be released

Question 5

What are the steps for sperm transport and capacitation?

Answer 5

1. Plasma membrane of the epididymal sperm is coated w proteins
2. During ejaculation, additional seminal plasma proteins associate with the sperm membrane
3. Within the female tract, proteins are removed and cholesterol is depleted -> sperm can now fertilise

Question 6

Steps of Fertilisation

Answer 6

1. Sperm weaves its way past cumulus granulosa cells aided by the enzyme hyaluronidase
2. Sperm binds to ZP3 molecules in zona pellucida causing a rise in Ca2+ lvl within sperm triggering acrosomal reaction
3. Acrosomal enzymes digest holes through zona pellucida clearing a path to the oocyte membrane
4. Sperm forms acrosomal process which binds to the oocyte’s sperm-binding receptors
5. The sperm and oocyte plasma membranes fuse allowing sperm contents to enter the oocyte
6. Sperm contents causes a rise in Ca2+ level in oocyte cytoplasm triggering cortical reaction, cell division, etc.

Question 7

What does Zona Pellucida do?

Answer 7

• mediates specific gamete interactions
• prevents polyspermy
• protects developing embryo from implantation

Question 8

When is the acrosome reaction triggered?

Answer 8

when sperm binds to ZP3

Question 9

What does the acrosome reaction do?

Answer 9

• causes a significant increase in intracellular Ca2+ levels
• high Ca2+ induces fusion of acrosome and plasma membranes and exocytosis of acrosome contents

Question 10

Ways to penetrate the zona pellucida

Answer 10

Question 11

How does the transition from an egg to an embryo occur?

Answer 11

Mammalian oocytes undergo periodic changes in cytosolic Ca2+ conc.
- promotes pronuclear development
- initiates embryonic gene expression
- etc.

Question 12

Steps of transitioning from egg to an embryo

Answer 12

1. After the sperm penetrates the secondary oocyte, the oocyte completes meiosis II forming ovum and second polar body
2. Sperm and ovum nuclei swell forming pronuclei
3. Pronuclei approach each other and mitotic spindle forms between them
4. Chromosomes of pronuclei intermix then DNA replicates in preparation for first cleavage division

Question 13

Summary of events leading to fertilisation

Answer 13

Question 14

What is the Acrosome?

Answer 14

= a unique membranous organelle located over the anterior part of the sperm nucleus
- contains a number of hydrolytic enzymes that, when secreted, help the sperm penetrate the egg’s coats