Topic.2.Development.powerpoint2.0.Fertilization

Question 1

What is fertilization?

Answer 1

formation of a diploid zygote from a haploid egg and sperm

Question 2

What are the key features of fertilization?

Answer 2

1. Recognition at a distance
2. Contact recognition and binding
3. Egg and sperm fusion
4. blocks polyspermy
5. Egg activation

Question 3

T/F: Sea Urchins have external fertilization

Answer 3

True,
Sea urchins, resact is released from the jelly layer into the surrounding seawater. Where sperm of the same species can bind to it.

Question 4

Explain how Sea Urchins recognize at a distance

Answer 4

Chemotaxis: The migration of cells towards a soluble concentration gradient of a stimulant.
Ex: Sea urchins-resact

Question 5

Resact

Answer 5

soluble glycoprotein derived from the jelly layer of the egg

Question 6

Explain contact recognition in sea urchins:

Answer 6

The egg jelly layer binds to receptor on the sperm plasma membrane through a carbohydrate molecule called fucose sulfate

Question 7

Acrosomal reaction in sea urchin:

Answer 7

acrosomal vesicle fuses with the plasma membrane causing the extracellular release of digestive enzymes that penetrate the jelly
coat.

Question 8

Explain the acrosomal process:

Answer 8

It’s a thin extension that grows out from the sperm to meet the vitelline envelope on the egg. The thin extension is made up of actin monomers that lengthen into actin filaments through a process of polymerization. The acrosomal process is covered by proteins, called bindin, that attach to receptors on the egg. The interaction is bindin species specific.The binding of the sperm to the egg completes the acrosomal reaction and allows the sperm’s plasma membrane to fuse with that of the egg.

Question 9

Explain egg and sperm binding in sea urchins

Answer 9

In the acrosomal process, the extension is covered by protein molecules called bindins that are attached to sperm-binding receptors on the vitelline layer of the egg. This binding is species-specific.

Question 10

Explain Blocks to polyspermy: Fast transient block
In sea urchins

Answer 10

Na sodium channels on the egg vitelline layer open, causing an inward influx of Na+ causing depolarization. Unfertilized eggs have a negative charge but become more positive upon fertilization. Thus having a positive charge, blocks other sperm from fusing.

Question 11

A fertilized sea urchin egg can be expected to be more negative or positive?

Answer 11

positive

Question 12

Explain the cortical reaction/ slow blocks to polyspermy in sea urchin

Answer 12

triggered by intracellular calcium release which causes cortical granules (vesicles) to fuse with the membrane. Enzymes released from granules clip receptors, lifting the vitelline layer, which then hardens to form the fertilization envelope. Sperm nucleus enters.

Question 13

in sea urchin cortical reaction, what triggers cortical granule fusion?

Answer 13

increase in intracellular calcium levels

Question 14

Cortical Granules fuse with the egg plasma membrane resulting in the release of:

Answer 14

-Proteinases & glycosidases
-mucopolysaccharides
-peroxidases
-hyalin protein

Question 15

Proteinases and Glycosidases

Answer 15

separate vitelline layer
from plasma membrane

Question 16

Mucopolysaccharides

Answer 16

produce an osmotic gradient that causes water to rush into the space between the plasma membrane and the vitelline envelope, causing the envelope to expand and become the fertilization envelope

Question 17

Peroxidases

Answer 17

crosslinks macromolecules of the vitelline membrane in order to harden the fertilization envelope

Question 18

Hyalin protein

Answer 18

modifies the extracellular matrix of the egg to help block sperm entry; coats outer surface of the egg

Question 19

Explain egg activation
-Early events
-late events

Answer 19

Early Events - increase in cell metabolism
Late Events - initiation of protein and DNA
synthesis in preparation of first cleavage (division)

Question 20

Zona pellucida; mammals

Answer 20

extracellular matrix of the egg

Question 21

T/F capacitation occurs in sea urchins

Answer 21

False, it occurs in mammals

Question 22

Explain capacitation:

Answer 22

substances secreted by uterus or fallopian tubes removes glycoprotein coat and seminal proteins from acrosome.

Question 23

Explain some key characteristics of capacitation:

Answer 23

– Increases sperm metabolism and motility
– Necessary for future sperm and egg binding
– Triggered by bicarbonate ions (HCO3–) in the vagina
– Requires about 5–6 hours in humans.

Question 24

What is the role of microvilli?

Answer 24

Microvilli in egg plasma membrane
help facilitate fusion

Question 25

Mammalian fertilization aims to make what step of oogenesis possible

Answer 25

Aims to explain the necessary steps in order for secondary oocyte to resume meiosis II, which is when the sperm penetrates the secondary oocyte

Question 26

Explain in general terms fertilization steps in mammalian

Answer 26

1) capacitation removes proteins from acrosome so sperm can be more motile and bind; triggered by basic HCO3- in vagina (5-6 hrs)
2) acrosomal enzymes dissolve zona pellucida (ECM of egg) and Ca+ flows in
3) sperm bind to zp3; zp2 and zp3 are cleaved and causes BLOCK
4) oocyte has 2nd meiotic division forming n ovum and polar body (12-36 hrs)
5) sperm and egg fuse DNA

Question 27

in mammalian fertilization, what is the acrosomal reaction?

Answer 27

when sperm comes into contact with the
oocyte’s zona pellucida (zp). Acrosomal enzymes begin to dissolve zp; actin
filament comes into contact with the zp.

Question 28

In mammalian fertilization, how does Ca+ influx affect cell?

Answer 28

It causes cortical granules inside the second oocyte then fuse to the outer membrane.

Question 29

The Zona Pellucida is
composed of three
proteins:

Answer 29

ZP1, ZP2 and ZP3

Question 30

Contact and Recognition in mammals:
Sperm plasma
membrane receptors
bind to what protein on Zona Pellucida?

Answer 30

ZP3

Question 31

What is the cortical reaction/slow block to polyspermy in mammalian fertilization?

Answer 31

released contents of the
cortical granules both
remove carbohydrate from
ZP3 so it no longer can bind to
the sperm plasma
membrane and partly cleave
ZP2, hardening the zona
pellucida

Question 32

How does the timing of fertilization between humans and sea urchins differ?

Answer 32

-First cell division in sea urchins occurs ~ 90 minutes after
fertilization
-In humans: 12-36hrs

Question 33

Explain sea urchin fertilization

Answer 33

1 sec: sperm contacts jelly egg coat
2 sec: acrosome breaks down jelly coat and bindin binds to the vitelline layer of the egg
20 sec: FAST block where Na+ enters egg; CORTICAL/SLOW block where Ca+ is released and vitelline layer hardens
5-40 min: egg is activated and increases metabolism to prep for first division at 90 min