Y2S2 P1 Reproductive Fertilisation
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Questions and Answers

What is the primary function of the acrosome reaction during fertilization?

  • To trigger the release of mitochondria from the sperm
  • To facilitate the binding of sperm to the oocyte
  • To promote egg maturation and meiosis
  • To dissolve the zona pellucida using enzymes (correct)
  • Which component of the zona pellucida specifically binds intact acrosome sperm and triggers the acrosome reaction?

  • ZP2
  • ZP1
  • ZP4
  • ZP3 (correct)
  • What is the role of CDK1 checkpoints in oocyte maturation?

  • To trigger cytokinesis after fertilization
  • To regulate transitions during meiosis II (correct)
  • To stimulate acrosome reaction in sperm
  • To maintain oocyte arrest at metaphase I
  • What is capacitation and where does it occur?

    <p>A time-dependent process allowing sperm to fertilize an egg in the oviduct</p> Signup and view all the answers

    What initiates egg activation after fertilization?

    <p>Release of Ca2+ leading to oscillations</p> Signup and view all the answers

    Which sperm protein is crucial for the fusion of sperm and egg membranes?

    <p>Izumo</p> Signup and view all the answers

    What is the effect of Ca2+ on sperm and oocyte during fertilization?

    <p>Triggers cortical granule exocytosis in the oocyte</p> Signup and view all the answers

    What happens to most mitochondria in the fertilized egg?

    <p>They are all inherited from the mother</p> Signup and view all the answers

    What is the significance of the ampulla in fertilization?

    <p>Location where egg and sperm fusion occurs.</p> Signup and view all the answers

    What triggers the acrosome reaction during fertilization?

    <p>Increase in intracellular calcium concentration in the sperm.</p> Signup and view all the answers

    Which event occurs during egg activation post-fertilization?

    <p>Cortical granule exocytosis.</p> Signup and view all the answers

    How does capacitation prepare sperm for fertilization?

    <p>It enhances the functional capabilities of the sperm tail.</p> Signup and view all the answers

    Which glycoprotein in the zona pellucida specifically binds acrosome-reacted sperm?

    <p>ZP2</p> Signup and view all the answers

    What role does calcium play in egg activation after fertilization?

    <p>Calcium is necessary for triggering cortical granule exocytosis.</p> Signup and view all the answers

    What occurs during the hyper-activated motility phase of sperm?

    <p>Sperm gain increased motile force.</p> Signup and view all the answers

    What happens to the centromeres of the fertilized egg?

    <p>They are predominantly inherited from the father.</p> Signup and view all the answers

    What role does calcium play in the acrosome reaction during fertilization?

    <p>Triggers exocytosis of hydrolytic enzymes</p> Signup and view all the answers

    Which of the following accurately describes the state of the oocyte before ovulation?

    <p>Arrested at metaphase II</p> Signup and view all the answers

    What is the primary feature of hyper-activated motility in sperm?

    <p>Enhanced mobility and force generation</p> Signup and view all the answers

    What happens to the centrosomal contribution in the fertilized egg?

    <p>All centrosomes come from the father</p> Signup and view all the answers

    Which glycoprotein in the zona pellucida binds to acrosome-reacted sperm?

    <p>ZP2</p> Signup and view all the answers

    During capacitation, which vital change occurs in sperm?

    <p>Gain of ability to penetrate the zona pellucida</p> Signup and view all the answers

    What is the role of the egg protein Cd9 in fertilization?

    <p>Facilitates cell adhesion and fusion</p> Signup and view all the answers

    How long can sperm fertilize an egg after capacitation?

    <p>1 to 2 hours</p> Signup and view all the answers

    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

    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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