Ras is a GTP-binding protein that is often defective in cancer cells. A signal from a growth factor through a receptor tyrosine kinase often stimulates normal cells to divide. When the receptor tyrosine binds the growth factor , Ras is stimulated to bind GTP. Ras in turn activates proteins that promote cell proliferation. A common mutation in cancerous cells causes Ras to behave as though it were bound to GTP all the time. B. Your friend decides that the signaling pathway involving the Ras protein is a good target for drugs design, because the Ras protein is often defective in cancer cells. Your friend designs a drug that will turn off the receptor tyrosine kinase by preventing it from dimerizing. Do you think that this drug will affect cells that have a defective Ras protein that acts as if it were always bound to GTP? Why or Why not?
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The normal signaling pathway involves the receptor tyrosine kinase binding to a growth factor, which then stimulates Ras to bind GTP. Show more…
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The relay protein Ras is part of the EGF pathway that promotes cell division (see Figure 9.10). The active form of Ras has GTP bound to it, whereas the inactive form has GDP. GTP is hydrolyzed to GDP and $P_{i}$ to switch Ras from the active to the inactive form. Researchers have discovered that certain forms of cancer involve mutations in the gene that encodes the Ras protein. Which of the following types of mutations would you expect to promote cell division and thereby lead to cancer? a. a mutation that prevents the synthesis of Ras b. a mutation that causes Ras to bind GDP more tightly c. a mutation that prevents the GTP bound to Ras from being hydrolyzed d. a mutation that prevents Ras from binding to Raf e. both b and c
K-Ras is a peripheral membrane protein involved in signaling pathways inside the cell. The protein is post-translationally modified with the molecule shown below. Which type of peripheral membrane protein is K-Ras? State the type of amino acid linkage between Ras and the molecule shown above. Draw a plausible mechanism for the reaction that would attach the molecule to the amino acid in Ras. Ras is an oncogene, meaning that it is often mutated or overexpressed in cancer cells. If an early stop codon mutation in Ras causes loss of the last 10 amino acids, would you expect the mutated version of Ras to interact with the membrane? Why or why not?
Sri K.
The Ras protein functions as a molecular switch that is set to its "on" state by other proteins that cause it to expel its bound GDP and bind GTP. A GTPase-activating protein helps reset the switch to the "off" state by inducing Ras to hydrolyze its bound GTP to GDP much more rapidly than it would without this encouragement. Thus, Ras works like a light switch that one person turns on and another turns off. You are given a mutant cell that lacks the GTPase-activating protein. What abnormalities would you expect to find in the way in which Ras activity responds to extracellular signals?
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