Biology Chapter on Polyspermy

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Questions and Answers

What is the result of polyspermy in sea urchins?

Normal cellular division

Formation of a diploid zygote

Production of more than one egg

Formation of a triploid nucleus (correct)

Which of the following is a mechanism used by sea urchin eggs to prevent polyspermy?

Production of additional sperm

Chemical inhibition of sperm motion

Electric change in the egg plasma membrane (correct)

Increase in egg size

What occurs during the fast block to polyspermy?

Cortical granules fuse with the plasma membrane

The sperm membrane ruptures

Egg cytoplasm expands rapidly

The electric potential of the egg plasma membrane changes (correct)

What happens to the chromosomes during polyspermy?

Chromosomes are distributed unequally among cells Signup and view all the answers

Why is the concentration difference of Na+ and K+ ions significant for the fast block to polyspermy?

It creates an electric potential difference Signup and view all the answers

How many poles are formed during the division of triploid chromosomes resulting from polyspermy?

Four Signup and view all the answers

What is the primary role of the plasma membrane during fertilization?

Inhibits the entry of sodium ions and prevents potassium ion leakage Signup and view all the answers

What causes the membrane potential of the sea urchin egg to change from -70 mV to +20 mV during fertilization?

Influx of sodium ions into the egg Signup and view all the answers

What kind of nucleus is formed when two sperms fertilize an egg in sea urchins?

Triploid nucleus Signup and view all the answers

What is the primary consequence of unequal chromosome distribution in cells resulting from polyspermy?

Some cells may die or develop abnormally Signup and view all the answers

What initiates the slow block to polyspermy in sea urchins?

Fusion of cortical granules with the plasma membrane Signup and view all the answers

What happens to a sea urchin egg's membrane potential during the fast block to polyspermy?

It becomes positive, preventing further sperm fusion Signup and view all the answers

How long does the fast block to polyspermy last after sperm binding?

1-3 seconds Signup and view all the answers

Which of the following best describes a method that can prevent polyspermy?

Artificially keeping the membrane potential positive Signup and view all the answers

What is the essential function of the cortical granule reaction?

To create a physical barrier to additional sperm entry Signup and view all the answers

What happens to the likelihood of polyspermy if sodium ion concentration is insufficient during fertilization?

The fast block to polyspermy may fail Signup and view all the answers

What function do proteases serve during the slow block to polyspermy?

They dissolve protein connections between the vitelline envelope and the cell membrane. Signup and view all the answers

What is the role of mucopolysaccharides during the slow block to polyspermy?

They produce an osmotic gradient causing water influx. Signup and view all the answers

What is the end result of peroxidase activity during the slow block to polyspermy?

It hardens the fertilization envelope by cross-linking tyrosine residues. Signup and view all the answers

What happens to the zona pellucida sperm receptors during the slow block to polyspermy in mammals?

They are modified so they can no longer bind sperm. Signup and view all the answers

What is the primary purpose of the slow block to polyspermy?

To prevent multiple sperm from fertilizing the egg. Signup and view all the answers

What structural change occurs due to mucopolysaccharides during fertilization?

Expansion of the fertilization envelope. Signup and view all the answers

What initiates the process of the slow block to polyspermy in sea urchins?

Cortical granule exocytosis begins. Signup and view all the answers

Which enzyme contained in mouse eggs cleaves N-acetylglucosamine from ZP3?

N-acetylglucosaminidase Signup and view all the answers

Study Notes

Prevention of Polyspermy

Polyspermy is the fertilization of an egg by multiple sperm.
In normal monospermy, a haploid sperm nucleus combines with a haploid egg nucleus to form a diploid zygote.
Polyspermy leads to abnormal development due to an unequal distribution of chromosomes.

Consequences of Polyspermy

In sea urchins, two sperm result in a triploid nucleus.
The centrioles of multiple sperm form multiple mitotic spindles, leading to abnormal cell division.

Block to Polyspermy

The fast block to polyspermy involves a rapid change in the egg's membrane potential.
The slow block to polyspermy involves the release of cortical granules from the egg.

Fast Block to Polyspermy

The resting membrane potential of the egg is approximately -70 mV.
The fast block involves a shift to +20 mV due to sodium ion influx.
This change in membrane potential prevents further sperm from fusing with the egg.
Confirmatory experiments show that artificially maintaining a negative membrane potential can induce polyspermy.

Slow Block to Polyspermy in Sea Urchin

Cortical granules release enzymes that modify the vitelline envelope.
These enzymes include proteases, mucopolysaccharides, peroxidase, and hyaline.
Proteases dissolve the protein connecting the vitelline envelope to the cell membrane, removing sperm binding receptors.
Mucopolysaccharides create an osmotic gradient, causing water to rush into the space between the plasma membrane and the vitelline envelope, leading to expansion.
Peroxidase hardens the fertilization envelope by cross-linking proteins.
Hyaline forms a coating around the egg, providing support for blastomeres during cleavage.

Slow Block to Polyspermy in Mammals

In mammals, the cortical granule reaction modifies the zona pellucida, preventing further sperm binding.
Cortical granules release enzymes that modify ZP2 and ZP3.
The enzymes include N-acetylglucosaminidase, which cleaves N-acetylglucosamine from ZP3 carbohydrate chains.
Proteases also clip ZP2, preventing its binding with sperm.

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Description

This quiz explores the mechanisms and consequences of polyspermy in fertilization. Learn about the fast and slow blocks that prevent multiple sperm from fertilizing an egg, as well as the implications of polyspermy on development. Test your knowledge of these critical biological processes.