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Receptor R is over expressed in CHO cells and analysed for expression. 6 × 10⁷ cells were incubated with its radioactive ligand (specific activity 100 counts per picomole). If the total counts present in cell pellet was 1000 cpm, the average number of receptors R per cell is (assume complete saturation of receptors with ligand and one ligand binds to one receptor) (A) 10⁴ (B) 10⁵ (C) 10⁶ (D) 10⁷
Receptor R is over expressed in CHO cells and analysed for expression. 6 × 10⁷ cells were incubated with its radioactive ligand (specific activity 100 counts per picomole). If the total counts present in cell pellet was 1000 cpm, the average number of receptors R per cell is (assume complete saturation of receptors with ligand and one ligand binds to one receptor)
(A) 10⁴
(B) 10⁵
(C) 10⁶
(D) 10⁷
Answer
Answer: (A) 10⁴
Total counts = 1000 cpm, and specific activity = 100 counts per picomole. Thus, total ligand bound = 1000 cpm / 100 counts per picomole = 10 picomoles. Given 6 × 10⁷ cells, average number of receptors per cell = 10 picomoles / 6 × 10⁷ cells = 10⁴ receptors per cell.
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