Fertilisation

Question 1

What are the important components of ejaculate

Answer 1

• seminal fluid secretions
  -prostate gland secretions

Question 2

What are the components of seminal fluid

Answer 2

-Fructose: provides a carbohydrate energy source for the sperm.

-Prostaglandins: cause the contraction of the smooth muscle in the uterus- causing it to move backwards- Retropulsion

-Coagulase: the sperm can leak out of the vagina, so this enzyme causes seminal and vaginal fluid to coagulate and adhere to the walls of the vagina.

Question 3

What are the components of the prostate gland secretion

Answer 3

• Fibrinolysin- breaks down the coagulation of the seminal and vaginal fluid
• Citrate: energy source
• Prostate specific antigen: This enzyme participates in the dissolution of the seminal fluid coagulum.

Question 4

Sperm motility in environment

Answer 4

sperm moves slowly through an acidic environment

sperm moves fast in an alkaline environment

Question 5

First step in Fertilisation

Answer 5

1. Capacitation reaction
   The capcitation reaction allows for only modified glycoproteins to remain on their surface. This allows for the hypermotility of the sperm. Only specialised glycoproteins remain on its cell membrane which are able to recognise ZP3 proteins on the zona pellucida.

Question 6

What is the second step in Fertilisation

Answer 6

The release of calcium which triggers the acrosomal reaction.
The cell membrane of the sperm opens up and the vessel of the acrosome fuses with the cell membrane and releases acrosomal enzymes such as acrosome and protease that break the zona pellucida

Question 7

What is the third step in Fertilisation

Answer 7

Release of genetic material & preventing polyspermy

The sperm head contains specialised proteins with an alpha and beta subunit.

1. Beta subunit binding

The beta subunit of the protein binds to the cell membrane of the oocyte, this activates channels in the cell membrane of the oocyte causing Na+ ions to enter the cell membrane, creating a positive charge near the cell membrane this is the fast-activating mechanism to prevent polyspermy.

2. Alpha subunit binding

When the alpha subunit of the protein binds, this causes the sperm to open its cell membrane and release its genetic material and haploid chromosomes into the oocyte. The binding of the alpha subunit also causes the release of calcium from the smooth endoplasmic reticulum. This stimulates lysosomes containing proteases to fuses with the cell membrane and release the hydrolytic enzymes which cause the break down of the zona pellucida wall and consequently form a hardened layer in the cell membrane to prevent polyspermy. The increased levels of calcium also allow for the secondary oocyte to complete its second meiotic division to form a definitive oocyte and a second polar body which is degraded. This allows for the male and female pronuclei to fuse and form a zygote.