Biology of Fertilization Processes

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Questions and Answers

Which of the following events is primarily responsible for beginning the metabolic processes in the egg after fertilization?

  • Regulation of sperm entry into the egg
  • Activation of egg metabolism to start development (correct)
  • Fusion of genetic material from the two gametes
  • Contact and recognition between sperm and egg

What role does the fusion of genetic material play in the process of fertilization?

  • It provides the necessary genetic information for the embryo. (correct)
  • It allows for the regulation of sperm entry.
  • It determines the sex of the embryo.
  • It initiates the metabolic activities of the egg.

What is the first step of the fertilization process amongst the listed events?

  • Contact and recognition between sperm and egg (correct)
  • Fusion of genetic material from the two gametes
  • Activation of egg metabolism to start development
  • Regulation of sperm entry into the egg

Which event directly controls how sperm is allowed entry into the egg?

<p>Regulation of sperm entry into the egg (C)</p> Signup and view all the answers

Which of the following statements correctly describes an outcome of the fertilization events?

<p>It prevents the entry of multiple sperm into the egg. (D)</p> Signup and view all the answers

What is the primary role of exocytosis in sperm function?

<p>To release enzymes from the acrosomal vesicle (C)</p> Signup and view all the answers

Which component does the sperm bind to during fertilization?

<p>Zona pellucida (B)</p> Signup and view all the answers

What process follows the sperm binding to the zona pellucida?

<p>Acrosomal reaction (C)</p> Signup and view all the answers

What is the function of enzymes released by the sperm's acrosomal vesicle?

<p>To break down the extracellular matrix (D)</p> Signup and view all the answers

What must occur before the sperm can pass through the extracellular matrix of the egg?

<p>Binding to the vitelline envelope (D)</p> Signup and view all the answers

What is the primary function of the extracellular layer surrounding the egg cell membrane?

<p>To assist in sperm recognition. (B)</p> Signup and view all the answers

Which of the following describes the extracellular layer found in most mammals?

<p>The thick zona pellucida. (C)</p> Signup and view all the answers

Which statement is true about the vitelline envelope?

<p>It plays a role in sperm recognition. (C)</p> Signup and view all the answers

What is the main difference between the zona pellucida and the vitelline envelope?

<p>The zona pellucida is thicker than the vitelline envelope. (B)</p> Signup and view all the answers

Which function is NOT associated with the extracellular layer surrounding the egg cell membrane?

<p>Regulating the maturation process of the egg. (A)</p> Signup and view all the answers

What initiates sperm motility during fertilization?

<p>Influx of Ca2+ ions (C)</p> Signup and view all the answers

What is the purpose of the resact gradient in fertilization?

<p>To attract sperm toward the egg (B)</p> Signup and view all the answers

What occurs during the acrosome reaction?

<p>Sperm release enzymes to penetrate the egg jelly (D)</p> Signup and view all the answers

Which of the following statements about the acrosome reaction is correct?

<p>It happens at the same time as sperm motility activation (B)</p> Signup and view all the answers

Which of the following is NOT involved in the initial approach of sperm to the egg?

<p>The presence of the acrosome reaction (B)</p> Signup and view all the answers

What primarily causes the fast block to polyspermy in sea urchin eggs?

<p>An influx of sodium ions (C)</p> Signup and view all the answers

What is the outcome of the lethality caused by blastomeres with different chromosome numbers in sea urchins?

<p>Embryonic death (D)</p> Signup and view all the answers

What is the result of the egg membrane's resting potential rising?

<p>Inhibition of sperm entry (B)</p> Signup and view all the answers

Which of the following mechanisms is considered a fast block to polyspermy?

<p>Electric potential change in egg (C)</p> Signup and view all the answers

Which of the following statements is true regarding polyspermy prevention in sea urchins?

<p>Fast block is reversible under certain conditions (A)</p> Signup and view all the answers

What occurs immediately after the fusion of the male and female pronuclei in sea urchins?

<p>DNA replication (D)</p> Signup and view all the answers

Which statement accurately describes the status of the zygote immediately after the fusion of the pronuclei?

<p>It forms a diploid nucleus containing combined genetic material. (C)</p> Signup and view all the answers

In sea urchins, what is the sequence of events after pronuclear fusion?

<p>DNA replication is initiated. (D)</p> Signup and view all the answers

Which best describes the outcome of pronuclear fusion in sea urchins?

<p>It establishes a diploid state in the zygote. (C)</p> Signup and view all the answers

What is the significance of DNA replication occurring after the fusion of pronuclei in sea urchins?

<p>It enables the diploid zygote to prepare for subsequent cellular processes. (B)</p> Signup and view all the answers

Flashcards

Sperm-Egg Recognition

The first step in fertilization, involving the sperm recognizing and attaching to the egg.

Sperm Entry Regulation

The process of ensuring only one sperm enters the egg, preventing polyspermy.

Fusion of Genetic Material

The merging of the sperm and egg's genetic material, forming a single cell called a zygote.

Egg Activation

The egg becomes metabolically active after fertilization, starting the process of embryonic development.

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Fertilization

The process of a sperm cell uniting with an egg cell, initiating the development of a new organism.

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Extracellular Layer

An outer layer surrounding an egg cell, often helping sperm recognize the egg.

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Vitelline Envelope

The extracellular layer surrounding the egg cell in most animals.

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Zona Pellucida

The thicker extracellular layer surrounding the egg cell in mammals.

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Sperm Recognition

The process where sperm cells attach to the extracellular layer of an egg.

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Acrosomal Reaction

The process where the sperm's acrosomal vesicle fuses with the cell membrane and releases enzymes.

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Sperm Binding

The attachment of the sperm to the outer layer of the egg.

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Sperm Penetration

The process of the sperm penetrating the egg's outer layer.

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Sperm-Egg Fusion

The fusion of the sperm and egg cell membranes, leading to the formation of a zygote.

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Sperm Motility Activation

Calcium ions (Ca2+) trigger the movement of sperm.

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Resact Gradient

Sperm swims in the direction of a higher concentration of a chemical called resact, released by the egg.

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Second Interaction

The acrosome reaction is triggered by a second interaction between the sperm and the egg jelly, a protective layer surrounding the egg.

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Fast Block to Polyspermy

The fast block to polyspermy is a rapid, temporary mechanism that prevents multiple sperm from fertilizing an egg. It works by changing the electrical charge of the egg cell membrane.

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Sodium Ion Influx

The influx of sodium ions into the egg cell membrane during the fast block makes the membrane more positive, preventing additional sperm from binding.

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Egg Membrane Potential Change

The fast block to polyspermy is caused by a change in the electrical potential of the egg cell membrane.

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Temporary Block

The fast block to polyspermy is a temporary measure, lasting only a few minutes. It buys time for a more permanent block to be established.

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Polypermy and Lethality

The fast block helps prevent polyspermy, which is the fertilization of an egg by multiple sperm. This is usually lethal because it leads to blastomeres with different numbers and types of chromosomes.

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Pronuclear Fusion

The male and female pronuclei combine to form a single nucleus containing a full set of chromosomes (diploid) in a sea urchin.

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DNA Replication after Fusion

The zygote nucleus, now having a complete set of chromosomes, starts to replicate its DNA. This is the first step in preparing for cell division and the development of a new organism.

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Diploid Zygote

A fertilized egg cell with a full set of chromosomes that will continue to develop.

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Sea Urchin Fertilization

The process by which a sperm cell unites with an egg cell, creating a zygote, the first cell of a new organism. In the context of sea urchins, the pronuclei fuse and DNA replication follows.

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Pronuclear Fusion in Sea Urchins

The process of merging the male and female pronuclei, each containing half a set of chromosomes, into a single nucleus with a full set of chromosomes.

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Study Notes

Developmental Biology Lecture 10: Fertilization

  • Fertilization: Two main functions:
    • Combining genetic material from two parents (sex)
    • Creating a new organism (reproduction)
  • Fertilization process (general):
    • Contact and recognition between sperm and egg
    • Sperm entry regulation into the egg
    • Fusion of genetic material from both gametes
    • Egg metabolism activation for development

Sperm Structure

  • Head: Contains a haploid nucleus and acrosome.
  • Acrosome: Derived from Golgi apparatus, contains enzymes to digest egg's extracellular coats.
  • Midpiece: Contains mitochondria and centriole that produces flagellum microtubules.
  • Tail: Provides energy for movement using mitochondrial ATP.

Egg Structure

  • Large cytoplasm: Stores ribosomes, nutritive proteins, and morphogenetic factors.
  • Protective agents: Present for survival in the specific environment.
  • Extracellular layers: Surround the egg's cell membrane, involved in sperm recognition; examples include vitelline envelope (most animals) and the zona pellucida (mammals).

Egg and Sperm Recognition

  • Five steps:
    • Chemoattraction of sperm to egg through soluble molecules secreted by the egg.
    • Exocytosis of sperm acrosomal vesicle and enzyme release.
    • Sperm binding to egg's extracellular matrix (like vitelline envelope or zona pellucida).
    • Sperm passage through the extracellular matrix.
    • Fusion of egg and sperm cell membranes.

External Fertilization in Sea Urchins

  • Steps:
    • Sperm contacts egg jelly layer
    • Acrosome reaction
    • Jelly layer digestion
    • Binding to vitelline envelope
    • Fusion of acrosomal process and egg membrane

Sperm Attraction

  • Chemotaxis: Sperm attracted by egg-secreted chemicals (like resact and speract in sea urchins).
  • Activation: Specific peptides (chemoattractants) increase sperm motility, providing directional movement.
  • Resact: Binds to sperm receptors; Leads to calcium channel opening; Activates sperm motility and directs it to the egg.

Acrosome Reaction

  • Two components:
    • Fusion of acrosomal vesicle with sperm cell membrane (exocytosis), releasing contents.
    • Extension of acrosomal process using globular actin to reach and fuse with the egg cell membrane.
  • Proteolytic enzymes: Released to digest protective egg coating, ensuring sperm access.

Bindin

  • Recognition: A protein on the sperm's acrosomal process recognized by protein complex on sea urchin egg's surface.
  • Gamete mediation: May be involved in gamete recognition and fusion in sea urchins.

One Egg, One Sperm (Monospermy)

  • Normal fertilization: Entry of only one sperm into the egg.
  • Polyspermy: Entry of two or more sperm, usually lethal.
    • Fast block: Change in the egg cell membrane's electrical potential (sodium influx) preventing further sperm entry (1-3 seconds).
    • Slow block: Cortical granules react with egg cell membrane, altering the vitelline envelope, creating the fertilization envelope, and preventing polyspermy.

Fusion of Genetic Material in Sea Urchins

  • Pronuclei: Male and female pronuclei carrying genetic material migrate and fuse.
  • Zygote nucleus formation: A diploid zygote nucleus formed by the merging of pronuclei.
  • DNA replication: Occurs after pronuclear fusion.

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Related Documents

BIO132 Lecture 10: Fertilization (PDF)

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