15. For successful fertilization in sea urchin, interaction between the surface of the egg and acrosomal proteins, specifically a 30.5 kDa protein called bindin, is necessary. The following factors could affect this interaction and prevent fertilization:
A. Removal of egg jelly polysaccharides.
B. Removal of bindin receptors on the egg vitelline membrane.
C. Removal of bindin receptors from the egg jelly.
D. Removal of bindin receptors from a single cluster on the vitelline membrane.

The factors that could affect the interaction between the sea urchin egg surface and the sperm acrosomal protein Bindin and thus prevent fertilization are:

• (A) Removal of egg jelly polysaccharides: This would interfere with initial sperm activation and chemoattraction since egg jelly contains molecules like Resact needed for guiding sperm.

• (B) Removal of Bindin receptors on the egg vitelline membrane: This would directly prevent species-specific binding of sperm to the egg and block fertilization.

• (C) Removal of Bindin receptors from the egg jelly: Incorrect, because Bindin receptors are located on the egg vitelline membrane, not the egg jelly.

• (D) Removal of Bindin receptors from a single cluster on the vitelline membrane: Likely insufficient to completely prevent fertilization since receptors are distributed and redundancy could compensate.

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Correct Factors That Affect Bindin-Egg Interaction and Prevent Fertilization:

A and B—Removal of egg jelly polysaccharides and removal of bindin receptors on the egg vitelline membrane—are critical to preventing fertilization. These two are essential components for sperm activation and species-specific binding, respectively.

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Introduction

Sea urchin fertilization is a carefully orchestrated event where the sperm protein Bindin plays a pivotal role in species-specific adhesion by binding receptors on the egg’s vitelline membrane. Several factors, including the composition of the egg jelly and presence of specific receptors, are critical for this interaction.

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Role of Egg Jelly Polysaccharides

The egg jelly coat contains polysaccharides and peptides such as Resact that activate and attract sperm. Removal of these polysaccharides hinders:

• Sperm activation processes such as the acrosome reaction.

• Chemotaxis toward the egg.

• Proper exposure and function of Bindin.

Thus, the egg jelly polysaccharides are essential prerequisites for Bindin to function effectively.

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Importance of Bindin Receptors on the Vitelline Membrane

Bindin receptors localized on the egg vitelline membrane facilitate specific binding of sperm Bindin protein to the egg surface. This binding is a species-specific lock-and-key interaction acting as a gatekeeper for fertilization. Removal or disruption of these receptors directly abolishes sperm binding and fertilization.

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Why Removal from Egg Jelly Receptors or Single Clusters Is Less Crucial

Bindin receptors are not known to be present on the egg jelly; rather, they reside on the vitelline membrane. Hence, removing receptors from the jelly doesn’t affect fertilization.

Additionally, removing receptors from only one cluster on the vitelline membrane is unlikely to completely block fertilization, as other receptor clusters may compensate for sperm binding.

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Conclusion

Successful fertilization in sea urchins depends on a functional egg jelly to activate sperm and the presence of Bindin receptors on the egg vitelline membrane to mediate sperm adhesion. Thus, removal of egg jelly polysaccharides (A) and Bindin receptors on the vitelline membrane (B) are major factors that disrupt sperm-egg interaction and prevent fertilization.

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This article sheds light on the molecular requirements of fertilization in sea urchins, emphasizing how specific disruptions in the egg environment can block successful reproduction.

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The best answer about factors preventing Bindin-mediated fertilization is:

A and B