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Questions and Answers
What is the primary function of the acrosome reaction during fertilization?
Which component of the zona pellucida specifically binds intact acrosome sperm and triggers the acrosome reaction?
What is the role of CDK1 checkpoints in oocyte maturation?
What is capacitation and where does it occur?
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What initiates egg activation after fertilization?
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Which sperm protein is crucial for the fusion of sperm and egg membranes?
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What is the effect of Ca2+ on sperm and oocyte during fertilization?
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What happens to most mitochondria in the fertilized egg?
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What is the significance of the ampulla in fertilization?
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What triggers the acrosome reaction during fertilization?
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Which event occurs during egg activation post-fertilization?
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How does capacitation prepare sperm for fertilization?
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Which glycoprotein in the zona pellucida specifically binds acrosome-reacted sperm?
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What role does calcium play in egg activation after fertilization?
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What occurs during the hyper-activated motility phase of sperm?
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What happens to the centromeres of the fertilized egg?
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What role does calcium play in the acrosome reaction during fertilization?
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Which of the following accurately describes the state of the oocyte before ovulation?
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What is the primary feature of hyper-activated motility in sperm?
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What happens to the centrosomal contribution in the fertilized egg?
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Which glycoprotein in the zona pellucida binds to acrosome-reacted sperm?
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During capacitation, which vital change occurs in sperm?
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What is the role of the egg protein Cd9 in fertilization?
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How long can sperm fertilize an egg after capacitation?
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Study Notes
Fertilization
- Fusion of egg and sperm, occurring in the ampulla of the oviduct.
- Requires calcium (Ca) for acrosome reaction, cortical granule exocytosis, and cell cycle progression.
Gamete Maturation
-
Egg:
- Undergoes nuclear and cytoplasmic maturation.
- Arrested at metaphase II of meiosis until ovulation.
- Resumes meiosis II after ovulation, with transitions controlled by CDK1 checkpoints.
-
Sperm:
- Acquire functionality and maturity in the epididymis but cannot fertilize an egg yet.
- Undergo capacitation in the female reproductive tract, a time-dependent process that takes 1-2 hours and enables sperm to fertilize an egg.
Penetration of Zona Pellucida
-
Capacitation:
- Enables sperm to penetrate the zona pellucida.
- Results in increased sperm tail functionality and motility.
- Allows for the acrosome reaction.
-
Acrosome Reaction:
- Exocytotic event where the plasma and acrosomal membranes fuse.
- Releases hydrolytic enzymes that dissolve the zona pellucida.
- Triggered by sperm binding to the ZP3 protein in the zona pellucida.
- Activated by an increase in intracellular Ca.
Zona Pellucida
- Composed of three glycoproteins (ZP1, ZP2, ZP3) synthesized by growing oocytes.
- ZP3 binds to the acrosome intact sperm, inducing the acrosome reaction by increasing intracellular Ca.
- ZP2 binds to acrosome reacted sperm.
Fusion of Oocyte and Sperm Membranes
- Proteins responsible for egg-sperm fusion:
- Cd9 (egg protein): Transmembrane protein involved in cell adhesion and fusion in other cells.
- Izumo (sperm protein).
Egg Activation
- Two major events triggered by Ca release:
- Cortical granule exocytosis.
- Resumption of the cell cycle.
- Fertilization stimulates Ca oscillations, which are necessary and sufficient for egg activation.
- All mitochondria are inherited from the mother.
- All centromeres are inherited from the father.
- Artificial fertilization through direct sperm injection into the egg is the basis of IVF (in vitro fertilization).
Cortical Granule Exocytosis
- Exocytosis of cortical granules triggered by Ca release.
- Prevents polyspermy (multiple sperm fertilizing the egg).
- Modifies the zona pellucida to block further sperm entry.
Fertilisation
- Fusion of egg and sperm in the ampulla of the oviduct
- Requires calcium (Ca) for acrosome reaction, cortical granule exocytosis, and cell cycle
Gamete Maturation
-
Egg:
- Oocyte maturation involves both nuclear and cytoplasmic development.
- Arrested at metaphase II until ovulation.
- Resumes meiosis II after ovulation.
- Transitions are regulated by CDK1 checkpoints.
-
Sperm:
- Acquire functionality and maturity in the epididymis but cannot fertilise an egg.
-
Capacitation in the female reproductive tract is required for fertilisation.
- This process takes 1-2 hours and is time-dependent, not location dependent.
Penetration of Zona Pellucida
-
Capacitation allows for penetration of the zona pellucida.
- Sperm tail becomes fully functional and highly mobile (hyper-activated motility).
-
Acrosome reaction:
- Release of hydrolytic enzymes that dissolve the zona pellucida.
- Fusion of plasma and acrosomal membranes.
- Induced by binding of sperm to ZP3, which causes an increase in intracellular calcium (Ca2+) within sperm.
Zona Pellucida
- Composed of three glycoproteins (ZP1, ZP2, ZP3).
- Synthesised by oocytes during growth.
- ZP3:
- Binds acrosome-intact sperm.
- Triggers acrosome reaction through an increase in intracellular Ca2+ in sperm.
- ZP2:
- Binds acrosome-reacted sperm.
Fusion of Oocyte and Sperm Membranes
- Proteins involved in egg-sperm fusion:
- Cd9: egg protein involved in cell adhesion and fusion.
- Izumo: sperm protein.
Egg Activation
- Triggered by calcium (Ca2+) release.
-
Two major events:
- Cortical granule exocytosis: Releases enzymes that modify the zona pellucida to prevent polyspermy (multiple sperm entering the egg)
- Resumption of the cell cycle: The egg divides and begins embryonic development
Cortical Granule Exocytosis
- Triggered by a rise in Ca2+ levels after fertilisation.
- Secretion of enzymes that alter the zona pellucida, preventing the entry of additional sperm.
- Essential for ensuring a single sperm fertilises the egg, resulting in a viable embryo.
Fertilization
- Fusion of egg and sperm
- Occurs in the ampulla of the oviduct
- Requires calcium for acrosome reaction, cortical granule exocytosis, and cell cycle
Gamete Maturation
- Requires two mature, fertile gametes: egg and sperm
-
Egg:
- Undergoes nuclear and cytoplasmic maturation
- Arrested at metaphase II until ovulation
- Resumes meiosis II after ovulation — transitions are controlled by CDK1 checkpoints
-
Sperm:
- Achieve functionality and maturity in the epididymis but cannot fertilize the egg
- Undergo capacitation in the female reproductive tract
- Not necessary for the sperm to be in the tract, but it is time-dependent
- Sperm become capable of fertilizing within 1–2 hours
Penetration of the Zona Pellucida
- After capacitation, sperm can penetrate the zona pellucida.
-
Capacitation:
- The sperm tail becomes fully functional and mobile
- Leads to hyperactivated motility; increased force generated
-
Penetration of the Zona Pellucida:
-
Acrosome reaction:
- An exocytotic event where the plasma and acrosomal membranes fuse
- Releases hydrolytic enzymes that dissolve the zona pellucida
- Induced by binding to the zona pellucida
- Activated by an increase in intracellular calcium
-
Acrosome reaction:
Zona Pellucida
- Composed of three glycoproteins (ZP1, ZP2, ZP3) synthesized by oocytes as they grow
-
ZP3:
- Binds acrosome intact sperm
- Induces the acrosome reaction by increasing intracellular calcium in the sperm
-
ZP2:
- Binds acrosome-reacted sperm
Fusion of Oocyte and Sperm Membranes
- Proteins necessary for egg-sperm fusion:
- Egg protein Cd9: A transmembrane protein involved in cell adhesion that can promote fusion in other cells
- Sperm protein Izumo:
Egg Activation
- Two major events:
- Cortical granule exocytosis
- Resumption of the cell cycle
-
Both are triggered by calcium release:
- Fertilization stimulates calcium oscillations
- Calcium is both necessary and sufficient for egg activation (no calcium, no activation; if calcium is present, it will activate the egg)
-
Inherited DNA:
- All mitochondria are from the mother
- All centromeres are from the father
-
In-vitro fertilization (IVF):
- Placing sperm directly into the egg can cause fertilization
Cortical Granule Exocytosis
- Further detailed notes on this topic would be helpful to provide a more comprehensive understanding of the process.
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