Concept explainers
A generic signaling cascade is shown in the following figure. A growth factor (GF) binds to a growth factor receptor, activating the kinase function of an intracellular domain of the growth factor receptor. One substrate of the growth factor receptor kinase is another kinase, kinase A, that has enzymatic activity only when it is itself phosphorylated by the GF receptor kinase. Activated kinase A adds phosphate to a transcription factor. When it is unphosphorylated, the transcription factor is inactive and stays in the cytoplasm. When it is phosphorylated by kinase A, the transcription factor moves into the nucleus and helps turn on the transcription of a mitosis factor gene whose product stimulates cells to divide.
a. | The following list contains the names of the genes encoding the corresponding proteins. Which of these could potentially act as a proto-oncogene? Which might be a tumor-suppressor gene?
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Though it is not pictured, the cell in the figure also has a phosphatase, an enzyme that removes phosphates from proteins—in this case, from the transcription factor. This phosphatase is itself regulated by kinase A. | |||||||||||||||||||
b. | What would you expect to be the effect when kinase A adds a phosphate group to the phosphatase? Would this activate the phosphatase enzyme or inhibit it? Explain. | ||||||||||||||||||
c. | Is the phosphatase gene likely to be a proto-oncogene or a tumor-suppressor gene or neither? | ||||||||||||||||||
d. | Several mutations are listed below. For each, indicate whether the mutation would lead to excessive cell growth or decreased cell growth if the cell were either homozygous for the mutation, or heterozygous for the mutation and a wild-type allele. Assume that 50% of the normal activity of all these genes is sufficient for normal cell growth.
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Genetics: From Genes to Genomes
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- Researchers have found that a certain signal transduction pathway, illustrated in the figure below, may be responsible for the development of cancer in pancreatic cells. In normal pancreatic cells, where the pathway remains inactive, a membrane-bound receptor called Ptc inhibits a downstream protein known as Smo. The inhibition of Smo blocks the activa- tion of a complex of proteins known as the HSC, which results in the cleaving of one of its proteins called Ci. The cleaving of Ci, in turn, prevents the pathway from initiating the syn- thesis of division-facilitating enzymes. A Ptc B Smo с inhibition D A model of a Ptc signal transduction pathway under normal conditions. HSC Ci cleavage A certain protein called the Hedgehog protein (Hh) is found to activate this signal transduction pathway and trigger uninterruptable cell division. cell division not initiated Which of the following describes the most plausible mechanism by which Hh triggers uninterruptable cell division? Hh binds to…arrow_forwardMany malignant tumors are characterized by the activation of one or more growth-factor receptors. What is the catalytic activity associated with transmembrane growth factor receptors such as the EGF receptor?arrow_forwardThe figure below shows how normal signaling works with a Ras protein acting downstream of a receptor tyrosine kinase. CYTOSOL active receptor tyrosine kinase Taratas THERI signal molecule 00 active signaling Q Search active Ras protein GTP 99+ Į SIGNALING Il app.honorlock.com is sharing your screen. ✡ active signaling protein Y aarrow_forward
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