The Biology Project > Cell Biology > Cell Signaling > Problem Set

Cell Signaling Problem Set

Problem 9: G-proteins

Tutorial to help answer the question

The endogenous GTPase activity of G-proteins serves to:

A.	stimulate the activity of enzymes by producing energy.
B.	synthesize cGMP as a second messenger.
C.	synthesize GTP as an energy source.
D.	hydrolyze GTP returning the G protein to a pre-stimulated level of activity.

Tutorial

Cellular responses to signals must be reversible. Ras is a G protein that is activated by exchanging GTP for bound GDP. The endogenous GTPase of Ras degrades the GTP back to GDP, inactivating the protein.

In some forms of cancer, mutations in Ras decrease the endogenous GTPase activity. The normal form of Ras is called a proto-oncogene and the mutant version an oncogene. Permanently activated Ras leads to unregulated cell division in the cancer.

The Biology Project > Cell Biology > Cell Signaling > Problem Set