The four glycoprotein hormones share a common alpha subunit. What determines the biological specificity of TSH, LH and FSH?

• A Alternative splicing of the alpha subunit gene in each pituitary cell type
• B Post-translational sulfation of the shared alpha subunit in thyrotrophs
• C The number of disulfide bridges in the alpha subunit
• D The unique beta subunit of each hormone, which confers receptor binding specificity ✓

Explanation

TSH, LH, FSH and hCG share an essentially identical alpha subunit encoded by a single gene. Each hormone has a distinct beta subunit that determines receptor recognition and therefore biological action, though full activity requires noncovalent association with the alpha subunit. Sulfation and splicing do not generate specificity here, and the alpha chain structure is conserved across all four hormones, so options B, C and A are incorrect.

Reference: Ganong Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.