A serum sample shows elevated glycoprotein hormone levels. Immunometric assays exploit the fact that TSH, LH, FSH, and hCG share which structural feature?
- A A common alpha subunit encoded by a single gene on chromosome 6 ✓
- B Identical beta subunits conferring biological specificity
- C A shared steroid-binding domain
- D An identical 198-amino acid single-chain structure
Correct answer: A. A common alpha subunit encoded by a single gene on chromosome 6
Explanation
TSH, LH, FSH, and hCG are glycoprotein heterodimers sharing a virtually identical alpha subunit (encoded on chromosome 6q), while hormone specificity resides in the unique beta subunit. Assays therefore use beta-subunit antibodies to avoid cross-reactivity. They contain no steroid-binding domain, and they are two-chain molecules, not single chains like GH or prolactin. This shared subunit also explains cross-talk seen in some tumours producing free alpha subunits.
Reference: Williams Textbook of Endocrinology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.