Fertilization

Question 1

What are the 4 stages of fertilization?

Answer 1

1. Recognition of egg by the sperm
2. Prevention of polyspermy
3. Activation of the egg metabolism
4. Fusion of the male and female pronuclei

Question 2

What is the difference between sex and reproduction?

Answer 2

Sex is the fusion of male and female pronuclei, reproduction is the production of a new individual

Question 3

Why do sperm need to be activated?

Answer 3

They are held inactive in the testes because they have limited energy

Question 4

What causes sperm to become active?

Answer 4

Changes in pH, temperature, or hormonal cues

Question 5

What is chemotaxis?

Answer 5

The sperm follow a chemical signal released by the egg

Question 6

What is the chemical sperm attractant in sea urchins?

Answer 6

Resact

Question 7

What is the chemical sperm attractant in amphibians?

Answer 7

Allurin

Question 8

What is thermotaxis?

Answer 8

Sperm are attracted to warmer temperatures. Seen in animals with internal fertilization because it is warmer near the ovaries

Question 9

What part of the egg does the sperm contact first?

Answer 9

The outer extracellular material. Either the jelly layer or the corona radiata and zona pellucida

Question 10

What is an acrosome?

Answer 10

A vesicle at the tip of the sperm with a bunch of enzymes

Question 11

What happens in the acrosome reaction in sea urchins?

Answer 11

Exocytosis of the acrosome is induced, and the globular actin right behind the acrosome forms a filament and pushes forward. Bindin is put out on the surface when the enzymes get released and they recognize the egg

Question 12

What initiates the acrosomal reaction in sea urchins?

Answer 12

Contact with the jelly layer

Question 13

What happens in the acrosome reaction in mammals?

Answer 13

Exocytosis happens, but mammalian sperm doesn’t have the actin. It relies only on the enzymes

Question 14

What initiates the acrosomal reaction in mammals?

Answer 14

Contact with the zona pellucida. The sperm can use their motility to get through the corona radiata

Question 15

What was the experiment that showed species specific recognition in sperm?

Answer 15

Looked at the interaction between bindin and ERB1 (on the egg). They coated beads in ERB1 and watched the response of the sperm. When the sperm and egg were the same species, the sperm was attracted to the bead and bound to the receptors. When the sperm was from a different species, the sperm weren’t attracted to the bead and didn’t bind very well

Question 16

Why is it important that the egg prevents polyspermy?

Answer 16

The zygote would have too many chromosomes, and cell division and chromosome segregation would get screwed up and the embryo would die

Question 17

What are the two blocks to polyspermy in sea urchins?

Answer 17

Fast block and slow block

Question 18

What stops polyspermy in mammals?

Answer 18

Just the slow block, no fast block present in mammals

Question 19

What happens in the fast block?

Answer 19

The membrane potential jumps to a positive value milliseconds after fertilization, where the inside of the cell becomes positively charged. The charge change messes up the shape of the receptors, so they lose their function

Question 20

What happens in the slow block?

Answer 20

Fertilization causes internal calcium stores to be released, which causes exocytosis of the cortical granules. The cortical granules eat the connections with the vitelline envelope and cause it to lift off and form the fertilization envelope

Question 21

What is contained inside the cortical granules?

Answer 21

Serine proteases that eat the connections with the vitelline envelope and proteoglycans that absorb water and cause the fertilization envelope to expand

Question 22

What causes activation of the egg metabolism?

Answer 22

Calcium

Question 23

How does the calcium get released from the ER when fertilization occurs?

Answer 23

Triggers the IP3 pathway. The sperm activates a tyrosine kinase, which activates phospholipase C, which breaks down PIP2 into DAG and IP3, then the IP3 diffuses through the cytoplasm and binds to channels on the ER causing calcium to be released

Question 24

What happens in the early stages of egg activation?

Answer 24

Activation of NAD+ kinase, which creates NADP+ and starts lipid metabolism. The hyaline layer is hardened and cross-linked

Question 25

What happens in the late stages of egg activation?

Answer 25

Regular translation and DNA synthesis machinery is reactivated, cell cycle resumes, membrane biosynthesis

Question 26

What has to happen to mammalian sperm before they are able to fertilize the egg?

Answer 26

They require capacitation

Question 27

What is capacitation?

Answer 27

Modifications done by the female reproductive tract to the sperm to make them able to fertilize the egg

Question 28

What modifications happen to the sperm during capacitation?

Answer 28

The metabolism is changed so the sperm can undergo acrosomal reaction, exposes the binding proteins ZP1 and ZP2, increases motility

Question 29

How does capacitation eliminate the need for the fast polyspermy block in mammals?

Answer 29

Capacitation becomes a time released mechanism, which limits the number of sperm that can reach the egg at a time