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Old 07-13-2011
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Question Insulin downstream signal disturbance

In a comparative study of two related cell lines, you find that one responds normally to insulin while the other has an impaired response. You discover that both cell lines bind insulin with equal affinity but that the impaired response is manifest in an inability to recruit the insulin response substrate-1 (IRS-1) protein to the receptor. This would most likely be due to which of the following?

(A) inability of the receptor to phosphory- late the RAS G-protein
(B) loss of activation of phospholipase C-gamma (PLC-g)
(C) mutation in the tyrosine phosphoryla- tion site of IRS
(D) serine phosphorylation of the insulin receptor preventing IRS binding
(E) tyrosine phosphorylation of the insulin receptor leading to the loss of the IRS binding site
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Old 07-13-2011
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(C) mutation in the tyrosine phosphorylation site of IRS
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Old 07-13-2011
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(D) serine phosphorylation of the insulin receptor preventing IRS binding
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Old 07-13-2011
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Is it CCCCCCCCCCCCCCCCC? What is the correct answer Jahn?
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Old 07-13-2011
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Quote:
Originally Posted by jahn77 View Post
In a comparative study of two related cell lines, you find that one responds normally to insulin while the other has an impaired response. You discover that both cell lines bind insulin with equal affinity but that the impaired response is manifest in an inability to recruit the insulin response substrate-1 (IRS-1) protein to the receptor. This would most likely be due to which of the following?

(A) inability of the receptor to phosphory- late the RAS G-protein
(B) loss of activation of phospholipase C-gamma (PLC-g)
(C) mutation in the tyrosine phosphoryla- tion site of IRS
(D) serine phosphorylation of the insulin receptor preventing IRS binding
(E) tyrosine phosphorylation of the insulin receptor leading to the loss of the IRS binding site
i think its C
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Old 07-13-2011
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Correct Answer Answer is C

The insulin receptor does not phosphorylate the RAS gene product (choice A). Loss of activation of PLC-g (choice B) would not prevent IRS proteins from binding to the activated insulin receptor.
Serine phosphorylation of the insulin receptor (choice D) is not involved in IRS binding.
Tyrosine phosphorylation of the insulin receptor results in the formation of IRS binding sites, not in the loss (choice E) of such binding sites.
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