W13-Animal Development

What are the two ways animals can reproduce?

Asexually and sexually

Which type of reproduction is more common in animals?

sexually

What are the 3 mechanisms of Asexual reproduction?

1. Fission

2. Budding

3. Fragmentation

When does sexual reproduction begin?

Fertilization

Describe fertilization

Fusion of a haploid egg and sperm to produce a diploid zygote

Where can sexual reproduction occur?

Either internally or externally

What kind of fertilization does sea urchin go through?

External fertilization

What is a acrosome?

A vesicle containing hydrolytic enzymes found in the sperm head of a sea urchin

What is Fast block to polyspermy?

The fast block to polyspermy is a rapid electrical change in the egg's membrane that prevents multiple sperm from entering after the first sperm fuses with the egg

What occurs before an acrosomal reaction can begin of a sea urchin?

• Sea urchin release eggs into the waters

• The eggs releases attractants that can cause the sperm to swim towards the egg

• As soon as the sperm reaches the jelly coat of the egg, molecules in the jelly coat trigger the acrosomal reaction in the sperm.

What does exocytosis of the acrosome of the sperm of a sea urchin lead to?

Exocytosis of the acrosome leads to release of the enzyme which results in partial digestion of the jelly coat

Describe the Acrosomal Reaction

Proteins on acrosomal proteins bind to sperm receptors

Importance for Acrosomal Reaction

Allows for species-species recognition

After proteins on acrosomal process bind to sperm receptors, what occurs?

• Fusion of plasma membranes occur.

• Fusion results in the opening of sodium channels in the egg’s plasma membrane

  • Na⁺ enters

As sodium channels are opened in the egg’s plasma membrane, what occurs?

• Na⁺ enters resulting in depolarization; a decrease in the membrane’s potential.

As Na⁺ enters the egg cell after fusion of the membranes of the sperm and egg cell, what are the resulting changes and what are their effects?

• Negative result on the outside of the membrane and Positive on the inside of the membrane

• Will result in the repulsion of any additional nearby sperm

• Preventing polyspermy - acting as a fast block to polyspermy

What prevents fast block to poplyspermy?

A change in charge as Na⁺ enters the egg cell leading to the inner membrane to have a positive charge and the outer membrane to have a negative charge

Describe Polyspermy

More than one sperm nuclei in the egg

Describe the process illustrated int he picture

What is the longer-lasting change that occurs as well to prevent polyspermy?

Slow block to polyspermy

Define the Vitelline Layer

Layer of glycoprotein attached to the plasma membrane.
(THE PURPLE PART)

What is found underneath the plasma membrane of the egg cell of a sea urchin?

vesicles called Cortical Granules

What does binding of a sperm to an egg of a sea urchin cause?

Causes release of Ca²⁺ from the ER to the cytosol

What does increase in Ca²⁺ causes on the sea urchin after sperm and egg cell binds?

Causes the cortical granules to release enzymes and other macromolecules into the space between the plasma membrane and the vitelline layer.

After cortical granules release enzymes and other macromolecules into the space, what does it trigger?

Triggers a cortical reaction, which lifts the vitelline layer away from the egg which is hardened to form a protective fertilization envelop.

What does the fertilization barrier do?

Provides a barrier against any additional sperm, leading to a slow block of polyspermy

After sperm enters the egg cell what occurs with the nuclei of both egg and sperm cell?

Sperm nucleus fuses with the egg nucleus which initiates and speeds up various metabolic reactions that will trigger embryonic development.

This process is called Egg ActivationW

What is egg activation?

What is a difference between sea urchin and mammals in terms of fertilization?

No fast block to polyspermy has been observed in mammals.