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BIOL-4501: Developmental Biology > Chapter 7: Fertilization > Flashcards

Chapter 7: Fertilization Flashcards

1
Q

organelle of the sperm that contains enzymes that digest proteins and sugars. Purpose?

A

acrosome. digests a path through the outer coverings of the egg. Made of Golgi apparatus derivatives.

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2
Q

an acrosome is made of

A

Made of Golgi apparatus derivatives.

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3
Q

globular actin is found between the nucleus and the acrosome. Actin extends ____ ___ from the sperm during early stages of fertilziation

A

acrosomal processes

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4
Q

primary motor portion of the flagellum. How is it organizaed/

A

axoneme. Made up microtubules that extend out of a centriole. Core of axoneme made up of 2 central microtubules surrounded by a row of 9 doublets of microtubules.

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5
Q

Core of axoneme made up of ____ central microtubules surrounded by a row of ___ doublets of microtubules.

A

Core of axoneme made up of 2 central microtubules surrounded by a row of 9 doublets of microtubules.

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6
Q

What motor protein is involved in flagellar movement

A

Dynein. ATPase. allows for sperm propulsion. allows outer doublet microtubules to slide past each other. ATP used dynein created by mid-piece mitochondria.

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7
Q

in mammals, the sperm is not mature until after it has been ejactulated. it must undergo ____ after the sperm has been inside the female reproductive tract for a prolonged period of time

A

capacitation

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8
Q

T/F the egg has more cytoplasm than the sperm

A

true. The sperm eliminates as much cytoplasm as possible, whereas the egg accumulates cytoplasm. The egg acts as a cytoplasmic store house.

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9
Q

when do oocytes produce their ribosomes?

A

during meiotic prophase.

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10
Q

in sea urchins, eggs contain thousands of different mRNA that remain ___ until after fertilization

A

repressed

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11
Q

What protective chemicals are found in an egg

A

1) UV filters
2) DNA repair enzymes
3) also may produce distasteful substances to avoid being eaten
4) yolks of birds contain antibodies that protect the embryo against microbes.

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12
Q

in sea urchins, the female pronucleus is ___ at the time of laying and fertilization. IN mammals, the egg is ___ until after the sperm’s nuclear material is already in the egg cytoplasm.

A

in sea urchins, the female pronucleus is HAPLOID at the time of laying and fertilization. IN mammals, the egg is DIPLOID until after the sperm’s nuclear material is already in the egg cytoplasm.

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13
Q

the large diploid nucleus of a primary oocyte

A

germinal vesicle.

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14
Q

list the layers of an egg from outer to inner most

A

1) egg jelly
2) vitelline envelope/ zona pellucida
3) cell membrane
4) cortex

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15
Q

egg jelly and vitelline envelope/zone pellucida are made largely of

A

fibrous mats of glycoproteins involved in sperm-egg recognition

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16
Q

proteins that anchor the vitelline envelope to the cell membrane

A

posts

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17
Q

the cortex is made of gel-like cytoplasms with ___ ___ that polymerizes to form ___ during fertilization

A

the cortex is made of gel-like cytoplasms with GLOBULAR ACTIN that polymerizes to form MICROFILAMENTS during fertilization

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18
Q

why is cortical egg cytoplasm thicker than other cytoplasms

A

because it contains more actin in the cytoplasm, making it less runny.

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19
Q

why does actin in the egg make microfilaments after fertilization?

A

necessary for cell division.

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20
Q

cortex contains

A

1) actin

2) cortical granules

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21
Q

waht do cortical granules contain? what is the purpose of cortical granules

A 
granules contain proteolytic enzymes.
contains
1) proteolytic enzymes
2) mucopolysaccharides
3) adhesive glycoproteins
4) hyaline protein. --> also provides support for cleavage-state blastomeres.
  • all involved in preventing polyspermy. Allows only one sperm to fertilize an egg.
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22
Q

in addition to the zona pellucida in a mammalian egg, what cells surround the egg? WHy?

A

cumulus cell layer. made of ovarian follicular cells that were nuturing the egg.

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23
Q

the inner most cumulus cells make up the ___ ___.

A

corona radiata: inner most layer of cumulus cells immediately adjacent to the zona pellucida and the egg cell membrane.

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24
Q

what layer does the sperm BIND to?

A

vitelline envelope or the zone pellucida.

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25
Q

recognition of egg and sperm

A

1) chemoattraction of sperm to egg by molecules released by egg
2) fusion and exocytosis of acrosomal vesicle, releasing the digestive enzymes to remove some egg jelly
3) sperm bind to extracellular matrix (vitelline envelope or the zona pellucida)
4) passage of the sperm through this extracellular matrix and closer to the egg nucleus
5) fusion of egg and sperm membranes.

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26
Q

in sea urchins, sperm are attracted toward eggs of the same species by ____:

A

chemotaxis: following a chemical gradient of chemicals secreted by the egg

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27
Q

when does a sea urchin egg start secreting chemotactic chemicals?

A

only when it is fully matured. Eggs can control the type of sperm the attract and when they attract them.

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28
Q

T/F: in sea urchins, sperm motility is only acquired after the sperm are spawned

A

true.

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29
Q

in sea urchins, why can’t sperm mature in the testes?

A

because the internal pH is kept low via high concentrations of HIGH CO2. Once ejaculated the pH is elevated, resulting in activation of dynein ATPase, which allows for flagellar movement.

30
Q

although dynein atpase activations allows the flagella to move once sea urchin sperm is in a less acidic environment, what allows the sperm to move in a specific direction?

A

direction of sea urchins motility is provided by SAPS: sperm activating peptides released from the egg jelly of sea urchin into the sea water to recruit sperm. Only attracts sperm of the same species.

31
Q

SAP mechanism for providing direction

A

1) SAP receptor on sperm binds the SAP/Resact that the Egg jelly released
2) binding results in cGMP cascade activation, producing cGAMP.
3) cGMP results in Ca2+ channel activation and results inCa2+ INFLUX into sperm
4) Ca2+ influx activates dynein arms (for motility), increases ATP output, and then sperm will swim up the resact concentration gradient until it finds the egg.

32
Q

2 components of the acrosomal raction

A

1) fusion of acrosomal vesicle with the sperm cell membrane. Exocytosis that releases acrosomal enzyme contents
2) extension of acrosomal process.

33
Q

acrosomal reaction is initiated by contact of the sperm with egg ___

A

egg jelly. contact triggers exocytosis. Proteolytic enzymes and proteosomes released begin to digest a path through the jelly coat to the egg cell surface (acrosomal process).

34
Q

after acrosomal protesomes digest a path to the egge cell surface, what happens?

A

the acrosomal process adheres to the vitelline envelope and tether the sperm to the egg.

35
Q

Explain the mechanism behind the acrosomal reaction and the formation of the acrosomal process

A

1) sulphate-containing polysaccharides in the egg jelly bind to specific receptors located directly above the acrosome vesicle
2) sulphate-binding activate s3 membrane proteins
- Ca2+ channel, allows Ca2+ influx into sperm
- Na+-H+ exchanger: Na+ in, H+ out of sperm.
- IP3 2nd messenger cascade. releases Ca2+ from inside the cell within the acrosome itself.

  • elevated Ca2_ triggers fusion of acrosomal membrane with the adjacent sperm cell membrane, releasing enzymes that can lyse a path through the egg jelly of the vitelline envelope.
  • once enzymes begin to digest a path through the egg jelly, the Ca2+ influx also triggers RHOB protein: helps organize actin cytoskeleton and promotes polymerization. Allows for globular actins to polymerize into filaments and EXTEND THE ACROSOMAL PROCESS.
36
Q

After burrowing through the egg jelly, the sperm must anchor to the egg cell membrane. How?

A

through bindin. a protein from the acrosome of the sperm binds to bindin receptors on dejellied eggs on the vitelline envelope, and helps tether the sperm to the egg.

Bindin receptors are species specific.

37
Q

once anchored via bindin-induced tethering, the ___ of egg and sperm can occur

A

fusion

38
Q

how does the fusion of egg and sperm cell membranes occur in sea urchins

A

1) actin polymerization in egg forms fertilization cone, which is homologous to the acrosomal process
2) actin from both gametes help widen the cytoplasmic bridge between the egg and the sperm.
3) Sperm’s nucleus and tail passes through the bridge.

39
Q

Which fusogenic proteins also help with membrane fusion between sea urchins egg and sperm cells in addition to actin?

A

Bindin also plays a secondary role as a fusogenic protein (it also helps anchor the sperm to the membrane after it burrows through the jelly).
Under ionic conditions, bindin can trigger the sperm and egg to fuse. After fusion, the sperm nucleus and tail passes through and is now in the egg

40
Q

2 primary ways of preventing polyspermy in sea urchins

A

1) fast block

2) slow block

41
Q

in sea urchins, the centriole provided by the ___ divides to form the 2 poles of the mitotic spindle while the centriole from the __ is degraded.

A

in sea urchins, the centriole provided by the SPERM divides to form the 2 poles of the mitotic spindle while the centriole from the EGG is degraded.

42
Q

explain the fast block mechanism against poly spermy in sea urchins

A
  • sperm contains NAADP that changes the cell membrane of the egg once the sperm has fused with the egg through the fertilization cone.
  • in the egg, Na+ channels are normally closed, preventing Na+ from entering the cell. After sperm fusion, the channels open and the membrane potential of the egg changes to a positive value (+20mV) By allowing sperm to trigger Na+ channel opening.
  • lasts one minute, prevents other sperm from binding for 1 minute.
43
Q

___ ___ removes any other sperm that are on the vitelline envelope after one sperm has fused within the cell membrane underneath

A

slow block

44
Q

slow black is accomplished via ___ ___ reaction

A

cortical granule reation: gets activated 1 min after fusion (after fast block in sea urchins)

45
Q

sperm entry and egg depolarization (because of Na+ channel opening) aids in slowblock, but when sperm fuses, it also releases soluble factors that results in Ca2+ channels opening, which then:

A

result in Ca2+ release from the ER of the egg TO the cytoplasm of the egg. This Ca2+ release causes egg cortical gradules to fuse with the egg membrane and exocytose their contents to promote slow block.

46
Q

when sperm enters, the granules fuse with egg cell membrane and exocytose their contents into the space between the __ ___ and the ___ ___

A

between the cell membrane and the vitelline envelope

47
Q

4 contributions of the cortical granule to slow block

A

1) serine protease: cleaves protein posts that connect the vitelline envelope to egg cell membrane.
- cleaves off bindin and attached sperm

2) mucopolysaccharides: causes fertilization envelope to be kept away from cell membrane
- absorbs H2O to expand space between membrane and envelope. Allows for radial expansion of fertilization envelope.

3) peroxidases and transglutaminases: forms cross links between proteins in the fertilization envelop (mucopolysaccharides and vitelline envelope) to stabilize the envelope
4) hyaline: forms coating around the egg to support and protect blastomeres during cleavage.

48
Q

cortical granules are tethered to the cell membrane via ___ ___ proteins that facilitate Ca2+ mediated exocytosis

A

integral membrane proteins that facilitate Ca2+ mediated exocytosis.
- as soon as Ca2+ is released from the ER of the egg, the cortical granules will fuse with the cell membrane above them.

49
Q

2 roles of Ca2+ rush when spem enters egg of sea urchins

A

1) causes a slowblock to polyspermy via release of cortical granules
2) releases inhibitors from maternal mRNA and allows for protein translation and allows for cleavage to occur.

50
Q

What releases Ca2+ from ER of egg to trigger cortical granule release? outline the mechanism

A

IP3.

  • upon sperm binding, soluble factors trigger the activation of PLC in the egg cell. PLC splits PIP2 into IP3 and DAG.
  • IP3 opens Ca2+ channels on the ER of the egg, which causes Ca2+ release into the cytoplasm of the egg
  • DAG activates PKC, which turns on Na+/H+ pump. Na+ moves into cell, while H+ moves out, resulting in EGG GOING ALKALINE.
  • in order for Na+/H+ pump to be activated, there must be Ca2+ .

Therefore, PLC activation results in 1) Ca2+ influx into cytoplasm and thus cortical granule release
2) alkalinzation of the egg.

51
Q
  • IP3 opens ____ channels on the ER of the egg, which causes ___ release into the cytoplasm of the egg
  • DAG activates___ , which turns on ___ pump. ___ moves into cell, while ___ moves out, resulting in EGG GOING ___.
  • in order for ____ pump to be activated, there must be ___.
A
  • IP3 opens Ca2+ channels on the ER of the egg, which causes Ca2+ release into the cytoplasm of the egg
  • DAG activates PKC, which turns on Na+/H+ pump. Na+ moves into cell, while H+ moves out, resulting in EGG GOING ALKALINE.
  • in order for Na+/H+ pump to be activated, there must be Ca2+ .

Therefore, PLC activation (thus the formation of IP3 and DAG from PIP2) results in 1) Ca2+ influx into cytoplasm and thus cortical granule release
2) alkalinzation of the egg.

52
Q

in addition to IP3 causing a Ca2+ ER release in Therefore, PLC activation results in sea urchins, what other mechanisms allow for A WAVE of Ca2+ release?

A

when IP3 causes Ca2+ release, Ca2+ binds to Ca2+ gated channels on the ER too, causing Ca2+-induced Ca2+ release.

53
Q

in sea urchins, PLC ___ isoform is activated to create IP3 in egg. ____ brought in by sperm to initiate Na+-influx depolarization also activates the enzyme cascade by leading to IP3 production and Ca2+ release.

A

in sea urchins, PLC GAMMA isoform is activated to create IP3 in egg. NAADP brought in by sperm to initiate Na+-influx depolarization also activates the enzyme cascade by leading to IP3 production and Ca2+ release

54
Q

Explain the mechanism behind the activation of PLCgamma when sperm binds to egg and releases soluble factors like NAADP.

A

sperm binding to VE via Bindin–> G protein activation –> (TRK) Src Activation —> PLCgamma activation –> PIP2 cleavage to DAG and IP3 –> Ca2+ release –> cortical granule exocytosis, inactivation of MAP kinase and cell cycle reinitiation.

55
Q

in early responses to Ca2+ ER release triggered by IP3, the same release of Ca2+ that is reponsible for the slow block cortical granule reaction is also responsible for:

A

mapkinase inactivation and the re-entry of the egg into the cell cycle and the reactivation of egg protein synthesis. Ca2+ activates metabolic reactions that initiate embryonic development.

56
Q

how does Ca2+ release from ER help with biosynthesis

A

Ca2+ activates metabolic reactions that initiate embryonic development. It activates NAD+ kinase, to convert NAD+ to NADP+ for lipid biosynthesis and fatty acid chain formation.

  • NADPH also helps regenerate glutathione and ovothiols: scavengers of free radicals.
  • Udx1: the enzyme used to cross link and support the fertilization envelope is also NADPH dependent.
57
Q

Summary of the Early responses to Ca2+ release

A

1) sperm and egg binding
2) polyspermy FAST BLOCK (Na+ depolarization)
3) sperm-egg membrane fusion
4) Ca2+ increase first detected.
5) cortical granule exocytosis.

58
Q

late responses of Ca2+ release

A
  • activation of a new burst of DNA and protein synthesis.
59
Q

in sea urchins, egg/sperm fusion causes intracellular pH to ____ via ______ exchange activation.

A

ph to rise because of Na+/H+ exchange mechanism. This Na+H+ exchanger was activated when PIP2 produces DAG (and IP3), which activates PKC, and turns on the Na+/H+ exchanger in response to calcium influx.

60
Q

during a late reponse, Ca2+ ____ MAPKinase, which does what

A

Ca2+ deactivates MAPK, removing the inhibition on DNA synthesis.

61
Q

While Ca2+ triggers DNA SYNTHESIS by MAPK inhibition, and the increase in pH stimulates this synthesis, how is initial PROTEIN SYNTHESIS started during the late response of egg activation

A
  • initial protein sythesis is reliant on mRNA already present in the oocyte cytoplasms. mRNAs encode for histones and morphogenic factors used in early embryonic development. mrNAs are typically inhibited by having their eIF4E 5’ end being bound by an inhibitor.
62
Q

mrNAs are typically inhibited by having their ___ ____ end being bound by an inhibitor. Upon fertilizaition, the ___ inhibitor becomes ___ and degraded, allowing ___ to complex with other translation factors and permit protein synthesis

A

mrNAs are typically inhibited by having their eIF4E 5’ end being bound by an inhibitor. Upon fertilizaition, the eIF4E inhibitor becomes phosphorylated and degraded, allowing eIF4E to complex with other translation factors and permit protein synthesis

63
Q

What process restores the mitotic cell division of the egg as a late response to Ca2+ release?

A

a key mRNA is cyclinB protein encoder. After cyclinB gets uninhibited by removal of the repressor at the eIF4E 5’ end, it combines with Cdk1 to create a mitosis-promoting factor (MPF) that initiates cell division.

64
Q

a key mRNA is ___ ___ ___ After___gets uninhibited by removal of the repressor at the eIF4E 5’ end, it combines with ___ to create a mitosis-promoting factor (MPF) that initiates cell division.

A

a key mRNA is cyclinB protein encoder. After cyclinB gets uninhibited by removal of the repressor at the eIF4E 5’ end, it combines with Cdk1 to create a mitosis-promoting factor (MPF) that initiates cell division.

65
Q

after sperm and egg cell membranes fuse in a sea urcchin species, the sperm ___ and its ___ separate from the mitochondria and flagellum, which both ___.

A

after sperm and egg cell membranes fuse in a sea urcchin species, the sperm NUCLEUS and its CENTRIOLE separate from the mitochondria and flagellum, which both DISINTEGRATE

66
Q

the centrosomes used to produce mitotic spindles in the egg comes from the ___

A

sperm (in sea urchins)

67
Q

once inside the egg, the sperm nucleus decondenses, exposing compact sperm to the egg cytoplasm. What happens after to facilitate DNA replication?

A

Kinases from egg phosphorylate sperm-specific histones, allowing the sperm chromatin to decondense (euchromatin)
- decondensed sperm histones are replaced by egg-derived cleavage-state histones. Sperm chromatin undergoes decondensation to form pronucleus.

  • once decondensed, the DNA adheres to thenuclear envelope, where DNA polymerase can initiate replication.
68
Q

Aster

A

integration of egg and sperm microtubules

69
Q

centriole from sperm are used to create the ___ required for mitotic spindle formation

A

create the centrosome.

70
Q

microtubules in seaurchins extent contact to the female pronucleus, allowing the two nuclei to migrate towards each other. Fusion creates a ____ ___.

A

Diploid zygote.

DNA synthesis can begin either in the pronucleus stage, or AFTER the formation of the zygote nucleus.

BIOL-4501: Developmental Biology (32 decks)

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