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Selenocysteine

Meaning

Selenocysteine is the 21st naturally occurring amino acid, a unique biological molecule structurally analogous to cysteine but containing a selenium atom instead of sulfur. It is an essential component for the function of numerous critical enzymes, collectively known as selenoproteins, which are primarily involved in antioxidant defense, redox regulation, and the metabolism of thyroid hormones. The body cannot synthesize it without selenium, making it a critical, non-negotiable micronutrient-dependent component of human biochemistry. Its presence is vital for maintaining cellular integrity and endocrine function.