Exchange of GDP for GTP GDP GTP Inactive Ras GDP protein Active Ras GTP protein GTP hydrolysts Cancer-causing mutations that prevent GTP hydrolysis keep Ras protein in the active state. FIGURE 25.12 Functional cycke of the Ras protein. The binding of GTP to Ras activates the function of Ras and promotes cell division. The hydrolysis of GTP to GDP and P; converts the active form of Ras to an inactive form. EGF receptor EGF Sos Ras Sos GRB2 Ras Raf-1 GDP GTP GRB2 Raf-1 GDP MEK MEK MAPK MAPKB Exposure to EGF Jun Jun -P Myc Fos Myc Fos -P Epidermal cell Pathway off Pathway on FIGURE 25.11 The activation of a cell-signaling pathway by a growth factor. In this example, epidermal growth factor (EGF) binds to two EGF receptors, causing them to dimerize and phosphorylate each other. An intracellular protein called GRB2 is attracted to the phosphorylated EGF receptor, and it is subsequently bound by another protein called Sos. The binding of Sos to GRB2 enables Sos to activate a protein called Ras. This activation involves the release of GDP and the binding of GTP. The activated Ras/GTP complex then activates Raf-1, which is a protein kinase. Raf-1 phosphorylates MEK, and then MEK phosphorylates MAPK. More than one MAPK may be involved. Finally, the phosphorylated form of MAPK activates transcription factors, such as Myc, Jun, and Fos. This leads to the transcription of genes, which encode proteins that promote cell division.
Exchange of GDP for GTP GDP GTP Inactive Ras GDP protein Active Ras GTP protein GTP hydrolysts Cancer-causing mutations that prevent GTP hydrolysis keep Ras protein in the active state. FIGURE 25.12 Functional cycke of the Ras protein. The binding of GTP to Ras activates the function of Ras and promotes cell division. The hydrolysis of GTP to GDP and P; converts the active form of Ras to an inactive form. EGF receptor EGF Sos Ras Sos GRB2 Ras Raf-1 GDP GTP GRB2 Raf-1 GDP MEK MEK MAPK MAPKB Exposure to EGF Jun Jun -P Myc Fos Myc Fos -P Epidermal cell Pathway off Pathway on FIGURE 25.11 The activation of a cell-signaling pathway by a growth factor. In this example, epidermal growth factor (EGF) binds to two EGF receptors, causing them to dimerize and phosphorylate each other. An intracellular protein called GRB2 is attracted to the phosphorylated EGF receptor, and it is subsequently bound by another protein called Sos. The binding of Sos to GRB2 enables Sos to activate a protein called Ras. This activation involves the release of GDP and the binding of GTP. The activated Ras/GTP complex then activates Raf-1, which is a protein kinase. Raf-1 phosphorylates MEK, and then MEK phosphorylates MAPK. More than one MAPK may be involved. Finally, the phosphorylated form of MAPK activates transcription factors, such as Myc, Jun, and Fos. This leads to the transcription of genes, which encode proteins that promote cell division.
Biochemistry
6th Edition
ISBN:9781305577206
Author:Reginald H. Garrett, Charles M. Grisham
Publisher:Reginald H. Garrett, Charles M. Grisham
Chapter30: Protein Synthesis
Section: Chapter Questions
Problem 15P
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How would a mutation that prevents the Ras protein
from hydrolyzing GTP affect the cell-signaling pathway in 25.11?
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