Question

1. What is an acrosomal reaction after egg and sperm first contact? What molecular interaction activates the acrosomal reaction? What is the purpose of acrosomal reaction?

2. What proteins on sperm tether the sperm to egg vitelline envelope? What would the consequence if this protein loses its specificity? (20 points)

3. What is polyspermy? What is the consequence of polyspermy?

4. What is the mechanism for fast block to polyspermy? What would be the influence on fertilization if the sodium concentration in the environment where fertilization occurs is too low?

Answer 1

1. An acrosomal reaction is a special kind of reaction where the acrosome if the sperm interacts with the egg to get fertilised. When the egg comes to contact with the sperm the plasma membrane fused with the sperm head which activates the acrosomal reaction. The acrosome release certain enzymes which there by defeat the zona pellusida and thus the sperm can reach the egg. The purpose of this reaction is to favour fertilisation.

2. It's the protein called vacqueir, it helps in dissolving the egg vitelline layer. If the protein losses it's specificity the binding of the sperm to the egg doesn't takes place hence the fertilisation also doesn't takes place.

3. Polyspermy is the situation when one egg is fertilised by more than one sperm. According to the number of the sperm that fertilize an egg the zygote will be triploid,tetraploid etc. The zygote will have extra genetic material and the Pattern of cell division will be abnormal.

4. Fast block of polyspermy is the situation in which the polyspermy is blocked. This is by the opening of Na+ channel when the sperm enters the egg. So when the sperm enters the egg the Na+ channel guides the Na+ to flow inside the egg and then the membrane potential changes and the new sperm can't enter the egg. If sodium concentration is too low this cannot be easy and thus the fertilisation won't be much easier.