T3: Fertilization Flashcards
what is the general idea of the viability of germ cells
the sperm is living longer then the oocyte (due to the trickle delivery)
what are the important events of fertilization
-capacitation
-sperm penetration between cumulus cells
-sperm attachment to zona pellucida
-sperm penetration to zona pellucida
-fusion of sperm and oocyte membranes
what state do sperm have to be in, in order to undergo the acrosome reaction
capacitated
when can sperm leave the oviduct sperm reservoir
when they are hyperactive
what expands the cumulus cell
when exposed to LH surge
where are the cumulus cells and what acid is found there
embedded in an extracellular matrix and contains hyaluronic acid
what are the roles of the zona proteins
ZP-1: structural support
ZP-2: helps an acrosome reacted sperm move through the zona
ZP-3: Zona protein that binds to a receptor on the sperm plasma membrane and induces the acrosome reaction
what must be completed before the sperm can fuse with the secondary oocyte
acrosome reaction
describe the overview of fertilization
-occurs when sperm comes into contact with the zona pellucida of the oocyte
-perforations develop in the acrosome
-point fusions of the sperm plasma membrane and the external acrosomal membrane occur
what is released during the acrosomal reaction and what is the importance
release of acrosome enzymes, enables sperm to penetrate the zona pellucisa
what is modified during the acrosomal reaction
the equatorial segment so that is can later fuse with plasma membrane of the oocyte
what happens during the acrosome reaction
the fusion of the plasma membrane of the sperm and zona pelluciuda, leads to vesiculation that creates pores though which the acrosomal enzymes can pass: this allows the sperm to penetrate through the zona pellucida
what happens after sperm penetration
when the sperm reaches the perivitelline space: it settles into a bed of microvilli
-plasma membrane of oocyte fuses with membrane of equatorial segment
-polyspermy blocked
what are supplementary sperm
-not problematic (doesn’t affect embryo development)
-extra sperm which pass through the ZP into the PV space
what are supernumerary sperm
-problematic/ enter the oocyte/ too much DNA
-extra sperm which succeed in entering the vitellus. Such ova are said to show polyspermy
what is polyspermy
when more than one sperm manages to enter the ovum (dispermy=2, triploidy=3), the fetus nearly always aborts
how is the zona reaction related to polyspermy
once sperm plasma membrane fuses w/ oocyte plasma membrane, the zona reaction occurs
-reaction makes the zona pellucida is impermeable to other sperms
-cortical granules undergo exocytosis
-the results in the zona block
what mediates the zona block
cortical granules (enzymes+ mucus polysacc)
what is triploidy
3 pronuclei in one zygotes
what is the vitelline block
reduction in the ability of the oocyte plasma membrane to fuse with additional sperm (mediated by cortical granules)
FAST REACTION
what is a slow oocyte block
zona reaction
what is the mechanisms of the blocks for sperm
-sperm attaches to the vitelline membrane
-cortical granules fuse to the vitelline membrane and release contents into perivitelline space
what happens after the block and how
-cortical granule components alter the zona: less penetrable by sperm
-vitelline membrane altered: less penetrable by sperm
how does the block of polyspermy relate to species
there is species variation for which block is used more
what are the factors causing decreased effectiveness of block to polyspermy
- Age of ova: aged oocyte increases chance of polyspermy
- heating ova: increases metabolism and lifespan of egg
3.excessive sperm numbers: sperm barriers reduce numbers at the AIJ, cervix, uterus, etc)
what are the last few steps of fertilization
-sperm is engulfed
-2nd meiotic division of oocyte is completed
-sperm nucleus decondenses(reduction in disulfide cross-links by glutathione- found in oocyte plasma membrane
-formation of male pronucleus
what are the number of polar bodies during certain stages
1 PB after the LH surge (ovulation)
2-3 PBs after fertilization
describe the fusion of pronuclei
- the male and female pronuclei are indistinguishable from one another
-the plasma membranes of the two pronuclei are dissolving and one diploid nucleus will remain
what is syngamy
membranes of the pronuclei break down chromosomes condense and arrange themselves for mitotic cell division
