Question 1

Which of the following best describes how Ras is inactivated in the insulin signaling pathway?

Accepted Answer

It is turned off by hydrolysis of its bound GTP to GDP.

Question 2

In a tumor cell line, Ras is mutated such that it is constitutively active. Which strategy would most effectively inhibit the growth of this tumor cell line?

Accepted Answer

Blocking insulin receptor autophosphorylation.

Question 3

Which of the following steps occurs immediately after insulin binds to its receptor on the cell surface?

Accepted Answer

Autophosphorylation of the receptor.

Question 4

What is the role of IRS-1 in insulin signaling?

Accepted Answer

It acts as a docking protein for downstream signaling molecules.

Question 5

Which of the following would most likely result from a mutation that prevents Ras from hydrolyzing GTP?

Accepted Answer

Continuous cell growth signaling.

Question 6

If PI3K is inhibited in the insulin signaling pathway, which downstream effect would be most directly affected?

Accepted Answer

Production of PIP3 from PIP2.

Question 7

Which of the following best explains why blocking insulin receptor autophosphorylation can inhibit tumor growth in cells with constitutively active Ras?

Accepted Answer

It prevents the initiation of the entire signaling cascade.

Question 8

Which molecule acts as a second messenger in the insulin signaling pathway after PI3K activation?

Accepted Answer

$$\mathrm{PIP}_3$$

Question 9

A patient has a mutation in IRS-1 that prevents its phosphorylation. Which process would be most directly impaired?

Accepted Answer

Recruitment of PI3K to the plasma membrane.

Question 10

Which of the following is a direct consequence of Ras activation in the insulin signaling pathway?

Accepted Answer

Activation of the MAP kinase cascade.

Insulin Signaling and Ras: Mechanisms and Regulation

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