When fertilization occurs, the sperm recognizes the egg by
Multiple Choice
the chemical messages the egg secretes into the interstitial space.
the much larger relative size of the egg.
the unique glycocalyx on the egg’s surface.
the strong acidity of the egg’s environment.
The Correct Answer and Explanation is :
The correct answer is: the unique glycocalyx on the egg’s surface.
During fertilization, the sperm’s recognition and binding to the egg are crucial steps that ensure species-specific reproduction. This recognition is primarily mediated by the unique composition of the egg’s glycocalyx—a carbohydrate-rich layer that envelops the egg’s plasma membrane. The glycocalyx consists of glycoproteins and glycolipids, which play a pivotal role in sperm-egg interaction.
One of the key components of the egg’s glycocalyx is the zona pellucida, an extracellular matrix composed mainly of glycoproteins. In mammals, specific glycoproteins within the zona pellucida, such as ZP3, serve as binding sites for sperm. When a sperm encounters the egg, proteins on the sperm’s surface recognize and bind to these glycoproteins, facilitating adhesion. This binding is highly specific, ensuring that sperm from the same species are more likely to successfully attach to and fertilize the egg.
Upon binding to the zona pellucida, the sperm undergoes the acrosome reaction—a process where the acrosome, a cap-like structure over the sperm’s nucleus, releases digestive enzymes. These enzymes help the sperm penetrate the zona pellucida, allowing it to reach the egg’s plasma membrane. Following penetration, the sperm and egg membranes fuse, leading to the combination of their genetic materials and the formation of a zygote.
The specificity of the interaction between sperm and the egg’s glycocalyx is vital for preventing cross-species fertilization and ensuring reproductive success. This mechanism underscores the importance of molecular recognition in reproductive biology, where precise interactions at the cellular level lead to the continuation of species.
In summary, the sperm recognizes and binds to the egg primarily through interactions with the unique glycocalyx on the egg’s surface, particularly the glycoproteins of the zona pellucida. This specific binding initiates a cascade of events culminating in fertilization and the development of a new organism.