T3: Fertilization

Question 1

what is the general idea of the viability of germ cells

Answer 1

the sperm is living longer then the oocyte (due to the trickle delivery)

Question 2

what are the important events of fertilization

Answer 2

-capacitation
-sperm penetration between cumulus cells
-sperm attachment to zona pellucida
-sperm penetration to zona pellucida
-fusion of sperm and oocyte membranes

Question 3

what state do sperm have to be in, in order to undergo the acrosome reaction

Answer 3

capacitated

Question 4

when can sperm leave the oviduct sperm reservoir

Answer 4

when they are hyperactive

Question 5

what expands the cumulus cell

Answer 5

when exposed to LH surge

Question 6

where are the cumulus cells and what acid is found there

Answer 6

embedded in an extracellular matrix and contains hyaluronic acid

Question 7

what are the roles of the zona proteins

Answer 7

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

Question 8

what must be completed before the sperm can fuse with the secondary oocyte

Answer 8

acrosome reaction

Question 9

describe the overview of fertilization

Answer 9

-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

Question 10

what is released during the acrosomal reaction and what is the importance

Answer 10

release of acrosome enzymes, enables sperm to penetrate the zona pellucisa

Question 11

what is modified during the acrosomal reaction

Answer 11

the equatorial segment so that is can later fuse with plasma membrane of the oocyte

Question 12

what happens during the acrosome reaction

Answer 12

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

Question 13

what happens after sperm penetration

Answer 13

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

Question 14

what are supplementary sperm

Answer 14

-not problematic (doesn’t affect embryo development)
-extra sperm which pass through the ZP into the PV space

Question 15

what are supernumerary sperm

Answer 15

-problematic/ enter the oocyte/ too much DNA
-extra sperm which succeed in entering the vitellus. Such ova are said to show polyspermy

Question 16

what is polyspermy

Answer 16

when more than one sperm manages to enter the ovum (dispermy=2, triploidy=3), the fetus nearly always aborts

Question 17

how is the zona reaction related to polyspermy

Answer 17

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

Question 18

what mediates the zona block

Answer 18

cortical granules (enzymes+ mucus polysacc)

Question 19

what is triploidy

Answer 19

3 pronuclei in one zygotes

Question 20

what is the vitelline block

Answer 20

reduction in the ability of the oocyte plasma membrane to fuse with additional sperm (mediated by cortical granules)
FAST REACTION

Question 21

what is a slow oocyte block

Answer 21

zona reaction

Question 22

what is the mechanisms of the blocks for sperm

Answer 22

-sperm attaches to the vitelline membrane
-cortical granules fuse to the vitelline membrane and release contents into perivitelline space

Question 23

what happens after the block and how

Answer 23

-cortical granule components alter the zona: less penetrable by sperm
-vitelline membrane altered: less penetrable by sperm

Question 24

how does the block of polyspermy relate to species

Answer 24

there is species variation for which block is used more

Question 25

what are the factors causing decreased effectiveness of block to polyspermy

Answer 25

1. Age of ova: aged oocyte increases chance of polyspermy
2. heating ova: increases metabolism and lifespan of egg
   3.excessive sperm numbers: sperm barriers reduce numbers at the AIJ, cervix, uterus, etc)

Question 26

what are the last few steps of fertilization

Answer 26

-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

Question 27

what are the number of polar bodies during certain stages

Answer 27

1 PB after the LH surge (ovulation)
2-3 PBs after fertilization

Question 28

describe the fusion of pronuclei

Answer 28

• 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

Question 29

what is syngamy

Answer 29

membranes of the pronuclei break down chromosomes condense and arrange themselves for mitotic cell division