Consider the following signal transduction pathway that is activated by the bind
ID: 101145 • Letter: C
Question
Consider the following signal transduction pathway that is activated by the binding of EGF ligand to its specific membrane receptor: 1. EGF (ligand) binds of the EGF receptor. 2. Ligand-bound EGF receptors become active through phosphorylation and become active. 3. Active EGF receptor causes Ras to exchange its bound GDP for GTP and become active. 4. Active Ras activates the kinase cascade (RAF, MEK and MAPK) through phosphorylation. 5. This increases the expression of c-myc gene, which promotes cell proliferation. 6. No signaling happens in the absence of EGF ligand. If mutated Ras protein continues to stay in its GTP bound form, then A) c-myc gene will keep being active and cancer will result B) EGF receptors will not become active through phosphorylation and dimerization C) the pathway will be activated irrespectively of EGF binding to the EGF receptor D) A and C E) B and C Oncogenic mutations can result from DNA rearrangements or duplications Consider the following scenario. Gene 1 encodes a protein that is always expressed at high levels. Gene 2 encodes a growth stimulating protein that is only expressed when the cell has received growth promoting signals. On occasion, Gene 2 gets positioned downstream of the promoter for Gene 1. What are the possible consequences? A) There will be no consequences for Gene 2 B) Gene 2 will lose its responsivity to growth promoting signals and will express at high levels C) Gene 1 will keep being expressed at high levels D) A and C E) B and CExplanation / Answer
64. D) A and C
RAS becomes active when it binds to GTP. Thus, if the mutated RAS protein continues to stay in its GTP bound form, it will continue to stay active. Active form of RAS will activate the kinase cascade which will increase the expression of c-myc gene, promoting cell proliferation. Thus, the active RAS-GTP will continuously result in promotion of cell proliferation and uncontrolled proliferation will result in cancer.
As the mutated RAS will stay active, the pathway will also stay activated irrespective of the binding of ligand to the receptor.