Multiple Choice
In a tumor cell line, Raf-1 is mutated such that it is constitutively activated by Ras even in the absence of insulin signaling. How can you inhibit the growth of this tumor cell line?
12. Biosignaling
Recap of Insulin Signaling As A Growth Factor
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How is Ras activity turned off?
A
It is turned off by phosphorylation.
B
It is turned off by hydrolysis of its bound GTP to GDP.
C
It is turned off by hydrolysis of its bound GDP to GTP.
D
It is turned off by hydrolysis of its bound GTP to GMP.
Verified step by step guidance1
Understand that Ras is a small GTPase, which means it is an enzyme that binds and hydrolyzes GTP (guanosine triphosphate).
Recognize that Ras activity is regulated by its ability to switch between an active and inactive state. The active state is when Ras is bound to GTP, and the inactive state is when it is bound to GDP (guanosine diphosphate).
Identify that the process of turning off Ras activity involves the hydrolysis of GTP to GDP. This reaction is catalyzed by the intrinsic GTPase activity of Ras, often accelerated by GTPase-activating proteins (GAPs).
Clarify that hydrolysis of GTP to GDP involves the cleavage of a phosphate group, converting GTP (a triphosphate) to GDP (a diphosphate), thus inactivating Ras.
Note that phosphorylation is not involved in turning off Ras activity; rather, it is the hydrolysis of GTP to GDP that inactivates Ras.
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