BIOL 370 Exam 2 questions with
complete solutions
What's the cause of the fast block of polyspermy in sea urchins? - correct answer ✔✔
Polyspermy: The entry of more than one sperm to an egg during the fertilization event.
Fast block of polyspermy: Achieved by changing the electric potential of the egg cell membrane.
• In sea urchin eggs, the egg cytoplasm contains relatively little sodium ion (Na+) whereas
seawater has a particularly high Na+. The reverse is the case of potassium ions (K+).
• The resting membrane potential of sea urchin eggs: about -70 mV. The inside of the cell is
negatively charged with respect to the exterior.
• The binding of the first sperm quickly shifts the membrane potential from -70 mV to about
+20 mV, which is caused by a small influx of Na+ into the egg.
• Sperm can fuse with membranes having a resting potential of -70 mV but not of any positive
resting potential.
• An electric block to polyspermy also occurs in frogs, but probably not in most mammals.
What's the cause of the slow block of polyspermy in sea urchins? - correct answer ✔✔ Slow
block of polyspermy: Accomplished by the cortical granule reaction
- increase in Ca2+ ions within the egg which triggers cortical granule reaction
- upon sperm entry, cortical granules fuse with the egg membrane
- release cortical granule serine protease into the space btwn the cell membrane and the fibrous
mat of vitelline envelope proteins
- causes cleavage of the proteins linking the vitelline envelope and the cell membrane
, - cortical granules then bind to vitelline envelope to form a fertilization envelope which helps
block polyspermy
Sea urchin gastrulation starts with the formation and invagination of a vegetal plate. Wnt
signaling seems to play a role in specifying the normal development of the mesoderm and
endoderm tissue in sea urchins. During normal sea urchin development, Wnt signaling
intracellular mediator β-catenin protein accumulates in the nuclei of the cells that will form
mesoderm and endoderm tissue. When sea urchin embryos were treated with litium chloride,
β-catenin accumulates in the nuclei of all blastula cells, the animal cells that should normally
become ectoderm tissue were converted to endoderm and mesoderm tissue. Conversely, if
early sea urchin embryos were injected with a ∆LvG-cadherin transgene, which prevents nuclear
localization of β-catenin, no endoderm or mesoderm was formed - correct answer ✔✔ · During
normal development, β-catenin in the Wnt signaling pathway accumulates predominantly in the
micromeres and some in the veg2 tier cells.
· When lithium chloride treatment permits β-catenin to accumulate in the nuclei of all blastula
cells, the animal cells become specified as endoderm and mesoderm.
· When β-catenin is prevented from entering the nuclei, the vegetal cell fates are not specified
and the entire embryo develops as ciliated ectodermal ball.
*** The LvG Cadherin transgene prevents the beta-catenin from accumulating in the nuclei of
the blastula, so instead of forming/specifying into endoderm and mesoderm, it forms a ciliated
ectodermal ball instead. Overall, Beta-catenin is important in specifying the vegetal cells of the
sea urchin embryo, and to form mesoderm and endoderm tissues
What is the Nieuwkoop center? Does it play a role in amphibian gastrulation? - correct answer
✔✔ The dorsalmost vegetal cells of the blastula, which are capable of inducing the organizer.
Yes it does play a role in gastrulation.
What is the cleavage pattern of amphibian and sea urchin embryos? Meroblastic or Holoblastic?
- correct answer ✔✔ Holoblastic
complete solutions
What's the cause of the fast block of polyspermy in sea urchins? - correct answer ✔✔
Polyspermy: The entry of more than one sperm to an egg during the fertilization event.
Fast block of polyspermy: Achieved by changing the electric potential of the egg cell membrane.
• In sea urchin eggs, the egg cytoplasm contains relatively little sodium ion (Na+) whereas
seawater has a particularly high Na+. The reverse is the case of potassium ions (K+).
• The resting membrane potential of sea urchin eggs: about -70 mV. The inside of the cell is
negatively charged with respect to the exterior.
• The binding of the first sperm quickly shifts the membrane potential from -70 mV to about
+20 mV, which is caused by a small influx of Na+ into the egg.
• Sperm can fuse with membranes having a resting potential of -70 mV but not of any positive
resting potential.
• An electric block to polyspermy also occurs in frogs, but probably not in most mammals.
What's the cause of the slow block of polyspermy in sea urchins? - correct answer ✔✔ Slow
block of polyspermy: Accomplished by the cortical granule reaction
- increase in Ca2+ ions within the egg which triggers cortical granule reaction
- upon sperm entry, cortical granules fuse with the egg membrane
- release cortical granule serine protease into the space btwn the cell membrane and the fibrous
mat of vitelline envelope proteins
- causes cleavage of the proteins linking the vitelline envelope and the cell membrane
, - cortical granules then bind to vitelline envelope to form a fertilization envelope which helps
block polyspermy
Sea urchin gastrulation starts with the formation and invagination of a vegetal plate. Wnt
signaling seems to play a role in specifying the normal development of the mesoderm and
endoderm tissue in sea urchins. During normal sea urchin development, Wnt signaling
intracellular mediator β-catenin protein accumulates in the nuclei of the cells that will form
mesoderm and endoderm tissue. When sea urchin embryos were treated with litium chloride,
β-catenin accumulates in the nuclei of all blastula cells, the animal cells that should normally
become ectoderm tissue were converted to endoderm and mesoderm tissue. Conversely, if
early sea urchin embryos were injected with a ∆LvG-cadherin transgene, which prevents nuclear
localization of β-catenin, no endoderm or mesoderm was formed - correct answer ✔✔ · During
normal development, β-catenin in the Wnt signaling pathway accumulates predominantly in the
micromeres and some in the veg2 tier cells.
· When lithium chloride treatment permits β-catenin to accumulate in the nuclei of all blastula
cells, the animal cells become specified as endoderm and mesoderm.
· When β-catenin is prevented from entering the nuclei, the vegetal cell fates are not specified
and the entire embryo develops as ciliated ectodermal ball.
*** The LvG Cadherin transgene prevents the beta-catenin from accumulating in the nuclei of
the blastula, so instead of forming/specifying into endoderm and mesoderm, it forms a ciliated
ectodermal ball instead. Overall, Beta-catenin is important in specifying the vegetal cells of the
sea urchin embryo, and to form mesoderm and endoderm tissues
What is the Nieuwkoop center? Does it play a role in amphibian gastrulation? - correct answer
✔✔ The dorsalmost vegetal cells of the blastula, which are capable of inducing the organizer.
Yes it does play a role in gastrulation.
What is the cleavage pattern of amphibian and sea urchin embryos? Meroblastic or Holoblastic?
- correct answer ✔✔ Holoblastic
