Which enzyme acts as a catalyst during the entry of sperm into the ovum?

Bihar CHO -2019

Obstetrics & Gynaecology

Easy

Appeared in: Bihar CHO -2019

Explanation

Hyaluronidase is an enzyme stored in and released from the acrosome, a specialized vesicle covering the head of the sperm.
Its primary function during fertilization is to depolymerize (break down) the hyaluronic acid polymers that act as intercellular cement for the cells of the corona radiata, the outermost layer surrounding the ovum.
By dissolving this layer, hyaluronidase creates a pathway for the sperm to navigate through the corona radiata and reach the next barrier, the zona pellucida.

Option B: Renin is an enzyme produced by the kidneys that is integral to the renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and fluid balance. It has no function in the reproductive process of fertilization.
Option C: DTH stands for Delayed-Type Hypersensitivity. This is a cell-mediated immune response that takes 24-72 hours to develop, such as in a tuberculin skin test. It is a process, not an enzyme, and is unrelated to fertilization.
Option D: Testosterone is the primary male sex hormone; it is a steroid, not an enzyme. While it is essential for spermatogenesis (the production of sperm), it does not act as a catalyst during the physical event of sperm penetrating the ovum.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Enzymatic process of fertilization as background academic context rather than a clinical decision trigger.
A defect in the acrosome reaction, such as insufficient hyaluronidase production, can be a cause of male infertility, as the sperm is unable to penetrate the ovum's protective layers.
What if a couple is infertile due to the male partner's sperm being unable to penetrate the egg? In such cases, assisted reproductive technology (ART) like Intracytoplasmic Sperm Injection (ICSI) can be used. This procedure bypasses the acrosome reaction entirely by injecting a single sperm directly into the ovum's cytoplasm.

How to Approach the Question

First, identify the key terms in the question: 'enzyme', 'catalyst', 'entry of sperm into ovum'. This directs you to the biochemical events of fertilization.
Recall the structure of the ovum and the barriers a sperm must cross: the corona radiata and the zona pellucida.
Consider how the sperm overcomes these barriers. This involves an enzymatic process called the acrosome reaction.
Evaluate each option. Hyaluronidase is an enzyme known to break down hyaluronic acid, the 'glue' of the corona radiata. This makes it a strong candidate.
Systematically eliminate the other options by identifying their primary biological roles: Renin (kidney/blood pressure), DTH (immune response), and Testosterone (hormone).
Conclude that Hyaluronidase is the only option that fits the description of an enzyme acting as a catalyst for sperm entry into the ovum.

Concept Tested & Keywords

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E6 Physiology Guyton 4SAE Part 3 p. 49-51