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?

Regulation of sperm entry into the egg Signup and view all the answers

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

It prevents the entry of multiple sperm into the egg. Signup and view all the answers

What is the primary role of exocytosis in sperm function?

To release enzymes from the acrosomal vesicle Signup and view all the answers

Which component does the sperm bind to during fertilization?

Zona pellucida Signup and view all the answers

What process follows the sperm binding to the zona pellucida?

Acrosomal reaction Signup and view all the answers

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

To break down the extracellular matrix Signup and view all the answers

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

Binding to the vitelline envelope Signup and view all the answers

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

To assist in sperm recognition. Signup and view all the answers

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

The thick zona pellucida. Signup and view all the answers

Which statement is true about the vitelline envelope?

It plays a role in sperm recognition. Signup and view all the answers

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

The zona pellucida is thicker than the vitelline envelope. Signup and view all the answers

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

Regulating the maturation process of the egg. Signup and view all the answers

What initiates sperm motility during fertilization?

Influx of Ca2+ ions Signup and view all the answers

What is the purpose of the resact gradient in fertilization?

To attract sperm toward the egg Signup and view all the answers

What occurs during the acrosome reaction?

Sperm release enzymes to penetrate the egg jelly Signup and view all the answers

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

It happens at the same time as sperm motility activation Signup and view all the answers

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

The presence of the acrosome reaction Signup and view all the answers

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

An influx of sodium ions Signup and view all the answers

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

Embryonic death Signup and view all the answers

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

Inhibition of sperm entry Signup and view all the answers

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

Electric potential change in egg Signup and view all the answers

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

Fast block is reversible under certain conditions Signup and view all the answers

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

DNA replication Signup and view all the answers

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

It forms a diploid nucleus containing combined genetic material. Signup and view all the answers

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

DNA replication is initiated. Signup and view all the answers

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

It establishes a diploid state in the zygote. Signup and view all the answers

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

It enables the diploid zygote to prepare for subsequent cellular processes. Signup and view all the answers

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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Description

This quiz explores the various processes involved in fertilization, including the roles of genetic material and the mechanisms that allow sperm to enter the egg. You'll examine key events that initiate metabolic activities in the egg and the significance of the extracellular layers during this process. Test your understanding of fundamental concepts in reproductive biology.