Early development & fertilization

What structure does sperm first penetrate during fertilization?

The corona radiata of the egg.

What helps sperm penetrate through the layers surrounding the egg?

Digestive enzymes of the acrosome.

What is ZP-3?

ZP-3 is an 83-kDa glycoprotein of the zona pellucida.

What does ZP-3 do?

ZP-3 binds to sperm at three sites.

Where is ZP-3 located?

In the zona pellucida.

What is the molecular size of ZP-3?

83 kDa.

How many sites does ZP-3 bind to sperm at?

Three sites.

What happens when sperm binds to ZP-3?

Sperm binding activates the acrosome reaction.

What is the acrosome reaction?

It is the reaction activated by sperm binding to ZP-3 that involves release of lysins/hydrolytic enzymes and changes that help the sperm penetrate the egg's surrounding layers.

What is released during the acrosome reaction?

Lysins such as hyaluronidase and other hydrolytic enzymes of the acrosome.

What is hyaluronidase?

A lysin released during the acrosome reaction.

What do the hydrolytic enzymes released from the acrosome do?

They break down the corona radiata.

What happens to intracellular pH during sperm activation?

Intracellular pH increases.

What ion movement causes intracellular pH to increase?

H+ efflux and Na+ influx.

Why does pH increase according to the notes?

The pH goes up due to loss of H+.

What happens to G-actin during fertilization?

G-actin is converted to F-actin.

What does F-actin form?

F-actin forms the acrosomal process, which is a filament.

What is the cytoskeleton made of according to the notes?

Actin.

What happens to the sperm when the acrosomal process forms?

The sperm elongates.

What is bindin?

Bindin is a 30-kDa protein.

What does bindin bind to?

Bindin binds to glycoproteins of the vitelline membrane/zona pellucida.

What is the molecular size of bindin?

30 kDa.

What happens when actin polymerizes through the perivitelline space?

It initiates contact between the sperm and egg plasma membranes.

What is the role of actin polymerization in fertilization?

It initiates contact between the sperm and egg plasma membranes.

What is the first step of the detailed fertilization sequence?

Sperm first penetrates the corona radiata of the egg.

What helps sperm penetrate the corona radiata?

Digestive enzymes of the acrosome.

What is the second step of the detailed fertilization sequence?

ZP-3 of the zona pellucida binds to sperm at three sites.

What is the third step of the detailed fertilization sequence?

Sperm binding activates the acrosome reaction.

What is the fourth step of the detailed fertilization sequence?

Hydrolytic enzymes of the acrosome are released to break down the corona radiata.

What is the fifth step of the detailed fertilization sequence?

Intracellular pH increases through H+ efflux and Na+ influx.

What is the sixth step of the detailed fertilization sequence?

G-actin is converted to F-actin, forming the acrosomal process.

What is the seventh step of the detailed fertilization sequence?

Bindin, a 30-kDa protein, binds to glycoproteins of the vitelline membrane/zona pellucida.

What is the eighth step of the detailed fertilization sequence?

Actin polymerization through the perivitelline space initiates contact between sperm and egg plasma membranes.

What is the ninth step of the detailed fertilization sequence?

The sperm nucleus, or pronucleus, is released into the egg.

What is the tenth step of the detailed fertilization sequence?

The egg is now fertilized, and meiosis II completes, leading to formation of the second polar body.

What is the eleventh step of the detailed fertilization sequence?

The egg is now diploid.

What happens to the sperm nucleus after sperm and egg membrane contact?

The sperm nucleus, called the pronucleus, is released into the egg.

What happens to meiosis II after the egg is fertilized?

Meiosis II completes, leading to formation of the second polar body.

What is the final ploidy of the fertilized egg?

Diploid.

What is a zygote?

A zygote is a one-cell organism that is formed after fertilization.

What is cleavage?

Cleavage is division without growth.

What is the relationship between cleavage and growth?

During cleavage, cells divide without growth.

What is found at the animal pole during cleavage?

The animal pole contains lots of small cells.

What is found at the vegetal pole during cleavage?

The vegetal pole contains many bigger cells.

What is a morula?

A morula is the 8–16-cell stage.

Are the cells of the morula equal in size?

No. The cells are not equal in size.

What are micromeres?

Micromeres are the cells at the top of the morula.

Where are micromeres located?

At the top of the morula.

What are macromeres?

Macromeres are the cells at the bottom of the morula.

Where are macromeres located?

At the bottom of the morula.

What is a blastula?

A blastula has 64+ cells.

What is the blastocoel?

The blastocoel is a pocket inside the blastula created when cells secrete fluid.

Where is the blastocoel located?

It is on the animal pole side.

What happens to cells to create the blastocoel?

Cells secrete fluid to create a pocket inside.

What is area opquae?

Area opquae is the darker region consisting of cells on top of the yolk.

What is area pellucida?

Area pellucida is the lighter region consisting of cells separated from the yolk.

What is the sequence from zygote to blastula described in the notes?

Zygote → cleavage → morula → blastula.

How many cells are present at the morula stage?

Approximately 8–16 cells.

How many cells are present at the blastula stage?

64+ cells.

What is the key difference between cleavage and ordinary cell division in the notes?

Cleavage involves division without growth.