Iron physiology — Which of the following is NOT considered a core function of iron in human biology?

Introduction / Context:
Iron is indispensable for hemoproteins and iron–sulfur proteins involved in oxygen transport, cellular respiration, and host defense. This question asks you to differentiate well-established roles of iron from statements that overreach into primary gene regulation, which is more characteristic of zinc and other DNA-binding factors.

Given Data / Assumptions:

• Hemoglobin and myoglobin (heme iron) transport/store oxygen.
• Cytochromes and iron–sulfur proteins drive electron transport and energy metabolism.
• Iron status influences immunity and neurodevelopment indirectly via enzymatic functions.
• Direct, sequence-specific gene regulation typically involves zinc-finger transcription factors (zinc-dependent), not iron as the primary genomic regulator.

Concept / Approach:
Discriminate between direct transcriptional regulation and metabolic support roles. While iron availability can modulate expression of certain mRNAs via iron-responsive elements (post-transcriptional control), iron is not a classic DNA-binding transcription factor metal in the way zinc is. Thus, “direct gene regulation as a primary genomic regulator” is the best “not a function” choice here.

Step-by-Step Solution:

Verification / Alternative check:
Biochemistry texts place iron’s centrality in heme enzymes and Fe–S clusters; regulatory roles exist but are ancillary and post-transcriptional.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing zinc’s core genomic role with iron’s metabolic and transport roles.

Final Answer:
Direct gene regulation as a primary genomic regulator.