Fertilization

zygote

when we are single celled

acrosomal reaction

sperm penetration of the egg

globular actin

elevated pH causes this of the acromosome to chaneg conformation and become filamentous actin

filamentous actin

forms the basis for the acrosomal process that is covered with glycoproteins

acrossomal process

as it is formed becomes surrounded by the sperm membrane again, which is covered in bindin molecules derived from the acrosomal contents

bindins

glycoproteins that cover acrosomal process

fast block of polyspermy

• when sperm cell membrane touches egg cell membrane, there is a rapid wave of depolarization that starts at the point and sweeps across the entire egg cell membrane

• rapid influx of Na+ into the egg causes the resting membrane potential to change from -70mV to +10mV

• this persists for about 3 seconds, during this time the egg membrane is no longer receptive to sperm, which have an overall positive charge

• it buys just enough time for the egg to get the slow block to polyspermy in place

slow block of polyspermy

• as a result of the Na+ influx into the egg, the stored Ca++ is releases inot the egg’s plasma

• the rising concentration of free Ca++ in the egg causes the cortical granules to bind to the inside of the egg cell membrane and then rupture the space between the egg cell membrane and the vitelline envelope called the perivitelline space

cortical granules

secretory structures placed under the egg cell membrane

cortical reaction

the rising concentration of the free Ca++ in the egg cuases the cortical granules to bind to the inside of the egg cell memebrane and then rupture to the space between the egg cell membrane and the vitelline envelope, called the perivitelline space

raising the fertilization membrane

dehydrated glycosaminoglycans-now exposed to water— hydrate, swell, and force the vitelline envelope out and away from the egg cell membrane, thus pushing any sperm away as well

metabolic activation of the egg

• begins with the Na+ influx associated with the fast block of polyspermy

  • look at slides

fusion of male and female pronuclei

• two pronucle migrate to one another, replicating their DNA as they go

• the chromosomes intermingle and line up at the metaphase plate for the first mitotic division, and fertilization officially come to an end

• a new human has now been established, as single celled zygote

capacitation

in which cholesterol and other molecules on the membrane of the sperm head are “washed off” making them more fragile and capable of fusing membranes with the egg

polar axes

• cranio-caudal (anterior posterior) axis = head-to-tail

• dorsoventral = back to front

animal pole

top of the egg where the cytoplasm has little to no yolk

vegetal pole

bottom of the egg where the cytoplasm is rich in yolk