Trace element nutrition — cobalt and vitamin B12 relationship Which statement correctly describes the role of cobalt in human nutrition with respect to vitamin B12 (cobalamin)?

Introduction / Context:
Vitamin B12 (cobalamin) contains a central cobalt ion coordinated within a corrin ring. Understanding this structural feature helps clarify why cobalt is essential in certain organisms and why free cobalt cannot substitute for the complex biological functions of B12 in humans, including methylmalonyl CoA mutase and methionine synthase reactions.

Given Data / Assumptions:

• B12 is obtained from diet or supplements; humans do not synthesize it.
• Cobalt is the metal at the core of cobalamin.
• Enzymatic activity requires the intact vitamin coenzyme, not ionic cobalt.

Concept / Approach:

Differentiate elemental cobalt from the organometallic coenzyme cobalamin. While cobalt is an integral part of B12, providing cobalt alone does not supply B12’s complex structure or coenzyme functions. Therefore, the combined statement affirming both facts is correct.

Step-by-Step Solution:

Verification / Alternative check:

Clinical deficiency symptoms (megaloblastic anemia, neuropathy) respond to B12, not to cobalt salts, validating the need for the intact vitamin.

Why Other Options Are Wrong:

Option D contradicts biochemistry; Option E is false because cobalt defines cobalamin; picking A or B alone is incomplete.

Common Pitfalls:

Assuming trace metal supplementation can replace complex coenzymes; it does not.

Final Answer:

Both (a) and (b)