Fertilization Flashcards
How are the gametes attracted during EXTERNAL fertilization
eg water by sea urchins
- female gamete releases specific substances from extracellular jelly for sperm to recognize- positive chemotaxis
- acrosomal reaction occurs
- Digestion of jelly layer(ALL SPERM GOES IN)
- Receptor mediated binding of sperm to vitelline envelope of egg
- fusion of acrosomal process and egg membrane
How to prevent polyspermy
fast block is when the egg plasma membrane changes electric potential
slow block is when cortical granule release
What is main difference between external fertilization and internal fertilization (mammals)
In external, acrosomal reaction triggered by extracellular coat of egg
In internal, acrosomal reaction triggered by zona pellucida, which is after the extracellular cumulus layer
What is acrosomal reaction (im guessing in mammlas?)
occurs after binding to zona pellucida
induced by zona proteins
releases enzymes :
hyaluronidase= penetration of the corona radiata barrier
trypsin-like substance =digestion of the zona pellucida
acrosin (zonalysin) =helps the spermatozoon cross the zona pellucida
What is sperm capacitation
When sperm acquires capacity to perform in fertilisation
- Final stages of sperm maturation that occurs in female repo tract
- ATP generating system gives sperm motility (due to modificstion of dyenin)
- Changes in plasma membrane- replacing cholesterol making membrane more fluid
What are 2 mechanisms to attract spermatozoa
Thermotaxis:capacitated spermatozoa can
sense thermal gradient along fallopian tube (in the
final part the temperature is about 2oC higher)
Chemotaxis: secreted molecules from cumulus
cells and oocyte.
What increases the hyperactivity of the sperm as it moves along fallopian tube
Ca 2+
How long is the process of fertilization in humans
24 hours- from when gametes fuse to first zygote division
Stages of fertilization
- First sperm moves across cumulus layer to zona pellucida. ZP contact triggers acrosomal reaction (hyaluronidase= corona radiata, acrosin= ZP)
- gametes fuse and polyspermy prevented
- Male and fem pronuclei formed.They possess nuclear envelope and contain haploid sets of chromosomes. They move towards each other.
- OOcyte finishes meiosis II and releases polar body
- The first mitotic spindle is arranged, then the zygote is divided into two blastomeres.
What happens when more than 1 sperm fuse
wrong number of chromosomes
spindle becomes multipolar rather than bipolar
What glycoproteins are in Zona pellucida
Zp glycoprotein matrix made during oocyte growth
contains ZP (ZP1, ZP2, ZP3 …).
What are the 2 major roles of ZP
Binds sperm
Activates acrosomal reaction after sperm bound
How does spermatozoon sense if
it is at the right place for activation of
acrosomal reaction.
Because there is A receptor on the sperm membrane
has to bind ZP in order to initiate the
acrosomal reaction.
ZP3 binding proteins in sperm plasma membrane (so acrosomal process not formed like in external)
Which sperm protein is essential for sperm egg fusion
IZUMO 1: immunoglobin at sperm head
localized at both the inner and
outer acrosomal membranes
What is the receptor for IZUMO 1 on the egg membrane and what is its role in preventing polyspermy
JUNO
JUNO disappears within 40 minutes of egg sperm fusion- prevents other sperm binding
Which region of the sperm head does membrane fusion occur
equatorial region- bc membrane on head tip already destroyed
What are some proteins involved in membrane fusion on sperm and egg
sperm: IZUMO 1, fertilin, ADAM family proteins
Egg: JUNO, integrins, cd9
How does IZUMO and JUNO cause membrane fusion
JUNO first binds to monomeric IZUMO1. The interaction is specific but weak.
An increased amount of JUNO gradually gathers to the attached site of the spermatozoon.
By the action of other proteins, IZUMO1 is folded and stays in firmly connected dimers.
The dimers are shorter than monomeric IZUMO1. That reduces the distance between egg and sperm
membranes. IZUMO1 no longer binds to JUNO and it leaves the complex.
What is the role of cd9
Involved in creation of microvilli and
microexesomes (small membrane vesicles
that facilitate membrane contacts).
What is the cortical reaction
cortical granules released upon fusion of of gamete membrane- BLOCKS POLYSPERMY
Content of granules:
- removes carbohydrates from ZP3 ( not able to bind to other sperm)
- Partly cleaves ZP2, hardening the zona pellucida
What happens to the oocyte after gamete fusion
- finshes second meiotic division and releases polar body
- formation of pronucleus
- replication of chromosomes
- Pronucleus migrates to centre
What happens to spermatozoon after gamete fusion
- protamines replace histones -compaction
- formation of male pronucleus
- Formation of microtubule aster
- replication of chromosomes
- Pronucleus migrates to centre
Why doesn’t the oocyte posses centrioles
To prevent parthenogenesis
How is the first centrosome formed in the egg?
Centriole imported from sperm to egg
Centriole duplicated during pronuclear phase = centrosome
What is the second centrosome needed for
needed to
arrange the fist mitotic spindle in the
zygote,
How do pronuclei move to each other
Microtubule aster bring the pronuclei to center of zygote
During this time, both pronuclei replicate DNA
Process mediated by cytoplasmic dyenin
Do the pronuclei ever fuse their nuclear envelopes?
NO
Only come into close contact
They wait until centrosome duplicated ( to arrange mieotic spindle) only then will their nuclear envelopes breakdown
