what is fertilization and what are the 2 main products of fertilization?
- - union of 2 germ cells (egg and sperm)
- - restoration of somatic chromosome number and activation of development process
what is chemoattraction?
molecules/chemicals that help sperm find the egg
what is the acrosome reaction?
the egg is covered in protective coating so the sperm has to break through it
what is preformation?
the formation of a tiny tiny person at the beginning that grows and grows
what did leeuwenhoek do?
he had really good glass tecniques so he could see very well through a microscope and he was the first to see little pond organisms and also SPERM! he thought they were little parasites
how does a germ cell turn into a mammalian sperm?
- cytoplasm is eliminated
- flagella forms
- golgi apparatus turns into the acrosomal vesicle and granule forms (has digestive enzymes that are involved in the acrosomal reaction)
- also has mictochondria and centrioles
- DNA compacts
what is a centriole?
microtubule organizing center that turns into a flagella
what are steps to development of sperm?
- meiosis forms the haploid spermatid
- then, spermiogenesis forms the sperm
what does a mature sperm NOT contain?
- no ribosomes
- no mRNA
- no transcription factors b/c DNA is so condensed
what is the structure of a sperm?
- from left to right:
- sperm head (acrosomal vesicle then nuclues) - midpiece (centriole, mitochondria) - tail
describe the flagella:
one axoneme: 9 microtubule dublets on the outside, 2 singles on the inside, dynein arms for movement, radial spokes, nexin
why are so many sperm produced?
to increase the odds, not many get in there
enters the vagina - up the cervical canal (3%) - uterus (.1%) - ismuths (of oviduct) - ampulla of oviduct (where the egg is) which is right above the ovary
what is the equatorial domain and where is it?
it is on the sperm cell membrane and it has proteins involved in initial fusion of lipid bilayers of membranes (integrin binds to integrin)
what happens after sperm docks on membrane?
the egg kind of extends a pseudopod absorbing the sperm
what are the 2 types of prevention of polyspermy in sea urchins?
describe what happens in the fast block
what ion makes it happen?
it happens immediately, and the membrane potential increases (from -70 to 30)
the receptor is on the sperm so the sperm cant bind when the membrane potential is this high
Describe the slow block:
- calcium triggers this, happens after 1 minute after fertilization, cortical granules release these things:
- 1) serine proteases to cleave the vitelline envelope posts and bind the binding receptors, blocking any sperm and removing bound sperm
- 2) GAGs that cause an osmotic gradient to form so water rushes in and the vitelline envelope turns into the fertilization envelope which RISES!
- 3) enzymes released that cause cross linking to harden the fertilization envelope
- 4) hyalin layer forms (coating around the outside), provides support for blastomeres during cleavage
what is the cortical granule reaction called in mammals and how is it different?
zona reaction - there is no rising fertilization envelope and the released enzymes modify the ZP sperm receptors
what causes release of cortical granules?
increase in intracellular calcium!
how is the sea urchin egg activated ?
- PLC (phospholipase C) splits up a molecule called PIP2 upon fertilization. PIP2 splits up into IP3 and DAG.
- IP3 - opens up calcium channels, to initiate cortical granule release
- DAG - triggers kinase C - opens up H+/Na+ ion exchange and increases the pH which induces protein synthesis, cell division, etc.
where does the calcium come from?
endoplasmic reticulum of the egg
what does release of calcium do?
cortical granule release - slow block to polyspermy and formation of hyalin layer
activation of NAD+ kinase - conversion of NAD+ to NADP+ - membrane biosynthesis
degradation of cyclin and inactivation of MAP kinase - restoration of mitotic cell cycle
what is the oocyte that mammals begin with?
secondary oocyte (it is stuck in metaphase II)
describe the beginning of the female reproductive tract:
- uterus does muscular contractions
- chemoattractive molecules
- lining is acidic (sperm have to change the pH from 4-7) but when they enter the cervix the pH is optimal for sperm
describe the cervical canal and mucus:
what are the diff types of mucus?
- epithelia have crypts
- viscosity of mucus is under endocrine control
- - E mucus: high estrogen, low progesterone (just prior to ovulation!), mucus is more watery so easier to swim through, mucus strands are parallell
- - G mucus: very viscous and disorganized, high progesterone, is like a web so resistant to sperm penetration
rapid transport and slow transport?
- rapid - majority of sperm - 5-20 mins, uterus contracts and increase in cilia so sperm can save their energy right before it gets to the egg
- slow - some sperm hang out in the cervical mucus for a couple days and then are released
what is sperm capacitation?
- series of changes before fertilization:
- 1) reorganization of plasma lipids (cluster on head of sperm)
- 2) loss of proteins on surface
- 3) increase pH and calcium (acrosome rxn)
- 4) membrane potential changes (loss of K+)
- 5) increase in cAMP
why is the human egg a diff size than the chicken egg?
human egg has placenta, chix egg is big bc everything it needs has to be inside the egg
what is inside the egg?
- proteins (energy supply and amino acids)
- ribosomes and tRNA
- mRNA (not translated till fertilization)
- components of rapid cell division
- cytoplasmic determinants (morphogenic factors)
what is egg path of meiosis?
primary oocyte (dogs) - first metaphase - second metaphase, will have 1 polar body (mammals) - meiosis complete, will have 2 polar bodies and 1 female pronucleus (sea urchins)
structure of sea urchin egg at fertilization:
- outside in:
- jelly layer (glycoproteins that have absorbed H2O), vitelline envelope (fibrous mat of glycoproteins), cell membrane, cortex with cortical granules and lots of G actin (makes filaments involved in cell division),
what connects the vitelline membrane to the cell membrane?
what is the vitelline envelope called in mammals? hows it diff?
zona pellucida (thicker)
hamster egg before fertilization?
- cumulus - equivalent to the jelly layer
- ovum - secondary oocyte
- corona radiata - inner most cells
how does chemoattraction work? whats an example of a molecule?
how much and what sperm is responsive to chemotaxis?
- sperm picks up more and more granules, influences how its flagella moves, it finds the egg
- - resact
- - about 10% and only the capacitated ones (thats why you send them in in waves)
roles of thermotaxis and chemotaxis:
- only capacitated sperm get it...
- thermotaxis is long term (warmer near the egg)
- chemotaxis is right before the egg - short term!
acrosome reaction in sea urchin:
- BIG PIC: sperm contacts jelly layer - acrosome rxn (sticks out acrosomal process, species specific egg jelly carbohydrates) - digests jelly layer - binds to vitelline envelope - fusion of acrosomal process membrane and egg membrane
- SPECIFIC RXN: calcium channel opens and calcium enters sperm head, sodium goes into sperm while H+ goes out of sperm, phospholipase enzyme makes IP3, globular actin turns into actin filaments so that the acrosomal process extends and releases enzymes, bindin on the sperm binds the acrosomal membrane to the plasma membrane of the egg
acrosome rxn in mouse:
- BIG PIC: sperm activated by female reproductive tract - glides through cumulus layer - binds to the zona pellucida - acrosome reaction - sperm lyses hole in zona - sperm and egg membranes fuse
- SPECIFIC: weak binding - slightly stronger binding to SED1 - even stronger binding to ZP3 - triggers acrosome rxn - calicum release then calcium mediated exocytosis - sperm docks flatly on the egg - receptors are clustered so all enzymes go in 1 direction to REALLY break through - ZP2 receptor on sperm holds sperm in place while its wiggling through
describe the zona pellucida:
- thick non cellular layer of glycoprotein
- made of 3 major glycoproteins (ZP1, ZP2, ZP3)
- binds sperm
- initiates acrosome rxn
possible immunocontraceptive target?
ZP3 - control animal populations by vaccinating them to make antibodies against their own ZP3