Chapter 13: Problem 1
The type of intercellular signaling in which one cell can communicate with another over long distances is called A. autocrine. B. endocrine. C. juxtacrine. D. paracrine. E. synaptic.
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Growth hormone releasing hormone (GHRH) produced by the hypothalamus binds to its pituitary receptor and leads to the production of growth hormone (GH) because of increase in cyclic AMP. Certain pituitary tumors result in hypersecretion of GH because of a mutation that produces a \(G_{s}-\alpha\) protein with a greatly diminished GTPase activity. Elements leading to increased cyclic AMP in response to GHRH binding to its receptor include A. activation of a monomeric G prorein. B. activation of adenylate cyclase by \(\alpha_{s}\) -subunit of a \(\mathrm{G}_{s}\) protein. C. activation of cyclic nucleotide phosphodiesterase. D. activation of protein kinase A. E. $ all of the above.
The ErbB/HER family of receptor tyrosine kinase genes are linked to many different types of human cancers. Overexpression of any of these genes would lead to an increase in the various receptors. ErbB2 encodes the HER2 protcin. This receptor does not bind any known extracellular growth factor, but it does form dimers with other growth-factor-bound HER receptors. Even modest overexpression of HER2 can alter normal cell growth regulation. Which of the following statements about receptor tyrosine kinases is correct? A. The catalytic domain is on the N-terminal end. B. Activation of the kinase requires ATP. C. Growth factor binding to the receptor triggers dimerization which activates the kinase activity. D. Active tyrosine kinase can phosphorylate other proteins but not itself. E. All of the above.
Growth hormone releasing hormone (GHRH) produced by the hypothalamus binds to its pituitary receptor and leads to the production of growth hormone (GH) because of increase in cyclic AMP. Certain pituitary tumors result in hypersecretion of GH because of a mutation that produces a \(G_{s}-\alpha\) protein with a greatly diminished GTPase activity. Low GTPase activity in the mutated protein results in consitutive activation of \(G_{s}\) and adenylate cyclase because A. GTP-bound \(\alpha\) -subunit does not reform the \(\alpha \beta \gamma\) trimer. B. GTP-bound G protein binds more strongly to the membrane receptor. C. GTP reacts directly with adenylate cyclase to activate it. D. the trimeric form of the G protein is stabilized. E. adenylate cyclase is phosphorylated more readily.
Manic depression may be caused by overactiviry of certain central nervous system cells, perhaps caused by abnormally high levels of hormones or neurotransmitters which stimulate phospholipidbased signal transduction (c.g., from phosphatidylinositol [PI]). Lithium has been used for many years to treat manic depression. In the presence of \(\mathrm{Li}^{*}\), the PI system is slowed despite continued stimulation and cells become less sensitive to these stimuli. Li \(^{+}\) may have two functions, inhibition of the phosphatase that dephosphorylates inositol trisphosphate and direct interference with the function of G proteins. Which of the following statements concerning G proteins is correct? A. G proteins bind the appropriate hormone at the cell surface. B. GTP is bound to G protein in the resting state. C. \(\alpha\) -Subunit may be cither stimulatory or inhibitory because it has two forms. D. Adenylate cyclase can be activated only if \(\alpha\) - and \(\beta\) -subunits of \(G\) protein are associated with each other. E. Hydrolysis of GTP is necessary for G protein subunits to separate.
Cells can terminate signal transduction by cell surface receptors by A. reducing agonist availability in the vicinity of the target cell. B. internalizing and degrading the receptor-agonist complex. C. modifying the receptor so that it is inactive or desensitized. D. all of the above. E. none of the above.
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