Biology: The Dynamic Science (MindTap Course List)
4th Edition
ISBN: 9781305389892
Author: Peter J. Russell, Paul E. Hertz, Beverly McMillan
Publisher: Cengage Learning
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Textbook Question
Chapter 9, Problem 13TYK
Discuss Concepts There are molecules called GTP analogs that resemble GTP so closely that they can be bound by G proteins. However, they cannot be hydrolyzed by cellular GTPases. What differences in effect would you expect if you inject GTP or a nonhydrolyzable GTP analog into a liver cell that responds to glucagon?
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Upon activation by a receptor, a G protein exchanges bound GDP for
GTP, rather than phosphorylating GDP that is already bound. Similarly,
the a subunit-GTP complex has a slow GTPase activity that hydrolyzes
bound GTP, rather than exchanging it for GDP. Describe experimental
evidence that would be consistent with these conclusions.
GTP is an important high-energy molecule that facilitates the activation of many cellular sig-
nal transduction pathways. Certain genetic dysfunctions can inhibit the ability of a cell to
synthesize GTP.
Which of the following describes the most direct result of GTP synthesis inhibition?
A
B
с
D
The cell would be able to carry out reception and transduction but would not be able to
produce the cellular response in the relevant signal transduction pathway.
The G protein-coupled receptor will not be able to bind corresponding ligands, inhibiting
the reception components of the relevant signal transduction pathway.
The cell will use ATP instead of GTP to activate the G protein on the intracellular region
of the G protein-coupled receptor.
The cell would not be able to activate G proteins on the intracellular regions of G pro-
tein-coupled receptors.
Many enzymes can hydrolyze GTP between the β and γ phosphates. The GTP analog β,γ-imidoguanosine 5′-triphosphate (Gpp(NH)p), shown below, cannot be hydrolyzed between the β and γ phosphates.
Predict the effect of microinjection of Gpp(NH)p into a myocyte on the cell’s response to β-adrenergic stimulation.
Chapter 9 Solutions
Biology: The Dynamic Science (MindTap Course List)
Ch. 9.1 - What accounts for the specificity of a cellular...Ch. 9.2 - Prob. 1SBCh. 9.2 - Prob. 2SBCh. 9.3 - Prob. 1SBCh. 9.3 - Prob. 2SBCh. 9.3 - Prob. 3SBCh. 9.3 - Prob. 4SBCh. 9.3 - Prob. 5SBCh. 9.3 - Prob. 6SBCh. 9.4 - What distinguishes a steroid receptor from a...
Ch. 9.4 - By what means does a specific steroid hormone...Ch. 9.5 - Prob. 1SBCh. 9 - In signal transduction, which of the following is...Ch. 9 - Which of the following could not elicit a signal...Ch. 9 - A cell that responds to a signaling molecule is...Ch. 9 - Prob. 4TYKCh. 9 - Prob. 5TYKCh. 9 - Which of the following is incorrect about pathways...Ch. 9 - Which of the following would not inhibit signal...Ch. 9 - Prob. 8TYKCh. 9 - Prob. 9TYKCh. 9 - Prob. 10TYKCh. 9 - Discuss Concepts Describe the possible ways in...Ch. 9 - Discuss Concepts Is providing extra insulin an...Ch. 9 - Discuss Concepts There are molecules called GTP...Ch. 9 - Discuss Concepts Why do you suppose cells evolved...Ch. 9 - How would you set up an experiment to determine...Ch. 9 - Prob. 16TYKCh. 9 - Prob. 1ITDCh. 9 - Prob. 2ITDCh. 9 - Prob. 3ITD
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- GTP-binding proteins play critical roles in many signal transductions through G proteins. Describe two examples in which G proteins act and compare the role of the G proteins in each case.arrow_forwardDescribe the general function and structural features of G-protein-coupled receptors (GPCRs). Be sure to include an explanation of GTPase activating proteins (GAPs) and GDP exchange factors (GEFs) in the context of the GTPase cycle. How are different classes of heterotrimeric G-proteins defined?arrow_forwardSignal-transducing heterotrimeric G proteins consist of three subunits designated α, β, and γ. The Gα subunit is a GTPase switch protein that cycles between active and inactive states depending on whether it is bound to GTP or to GDP. Review the steps for ligand-induced activation of effector proteins mediated by the heterotrimeric G proteins. Suppose that you have isolated a mutant Gα subunit that has an increased GTPase activity. What effect would this mutation have on the G protein and the effector protein?arrow_forward
- Some strains of bacteria or microorganisms have developed toxins that can modify the activity of the alpha subunit of G proteins which results in disease. For ex. cholera toxin, produced by Vibrio cholerae, causes ADP ribosylation of the stimulatory Gαs subunit of G proteins. This modification abolishes the GTPase of Gαs, and results in an αs subunit that is always in the “on” or active state. It results in continuous stimulation of adenylyl cyclase (AC). The main cells affected by this are the epithelial cell in gastrointestinal tract. Knowing this altered activity of AC, explain why patients affected by this toxin experience severe diarrhea and dehydration that may result in death.arrow_forwardIn response to nitric oxide signaling in the male genitalia, GTP is cyclized to produce 3’-5’ cyclic GMP (cGMP): cGMP stimulates vasodilation and produces an erection. Viagra (Sildenafil) is a selective inhibitor of cGMP-specific phosphodiesterase type 5 (PDE5), which is responsible for degradation of cGMP. Based on this information, do you expect that Viagra can produce a spontaneous erection in the absence of a stimulus? Provide a short (one sentence) rationale for your answerarrow_forwardBriefly describe the following properties of the Rab and Arf GTPases: a) Size, structure and cellular localization (for structure I want to know if they are lipidated and any other unique features) , b) How are they activated and inactivated (i.e. include the GEFs and GAPs), c). Give an example of downstream cellular effects.arrow_forward
- Ligand binding to proteins may occur with varying strengths; some ligands bind tightly to proteins while others bind less tightly. The strengths of reversible binding are determined experimentally by varying concentrations of ligands, and measuring the saturation of the protein in the various ligand concentrations. One such laboratory study investigated the binding of a hormone to three different receptor proteins in the cell membrane. The data collected are shown in the table below: 1) Provide a brief explanation as to why ligand binding to proteins must be a reversible process. 2) Calculate the dissociation constant (Kd) for the hormone binding to each of the three proteins.arrow_forwardIn studies trying to understand the regulation of hormone-sensitive adenylatecyclase, it was discovered that non-hydrolyzable GTP analogs and cholera toxin (that inhibits theGTPase activity of Gs ) were able to activate the enzyme in a sustained (irreversible) profile, thereforeindicating that GTP hydrolysis represents a deactivation (turn-off) regulatory step.a) Will these analogs or toxin have any effect on adenylate cyclase activity in the absenceof any added hormone?b) If you add an factor that increases the rate of GTPase hydrolysis of the Gs protein, willthis activate or inhibit the observed downstream effect upon addition of the hormone (this is in theabsence of GTP analogs or toxin). Explain your answer.arrow_forwardSignaling activity of G proteins is controlled by GTPase activating proteins (GAPs) and Guanine exchange factors (GEFs). What are the mechanisms by which GAPS and GEFs control G protein functions? GEFS inhibit G protein functions by stimulating GTP hydrolysis; GAPs activate G protein functions by stimulating GDP-GTP exchange. O GAPS inhibit G protein functions by stimulating GTP hydrolysis; GEFs activate G protein functions by stimulating GDP-GTP exchange. GEFS inhibit G protein functions by stimulating GTP hydrolysis; GAPS activate G protein functions by inhibiting GDP-GTP exchange. GAPs stimulate G protein functions by blocking GTP hydrolysis; GEFS inhibit G protein functions by stimulating GTP-GDP exchange. GAPS inhibit G protein functions by stimulating GDP-GTP exchange; GEFS activate G protein functions by stimulating GTP hydrolysisarrow_forward
- Receptor tyrosine kinases such as the epidermal growth factor (EGF) receptor can basically be broken down into three domains: (1) An extracellular, ligand binding domain, (2) A transmembrane domain that must cross through the cell membrane, and (3) an intracellular domain. Match the amino acid with the domain that it would MOST LIKELY be associated with. Lysine (choose (1), (2), or (3) from above) A tyrosine residue capable of being phosphorylated on its hydroxyl group (choose (1), (2), or (3) from above) Isoleucine (choose (1), (2), or (3) from above)arrow_forwardIn the case of GPCR (G protein coupled receptor) signaling pathways, which of the following statements is INCORRECT? The gamma subunit of the trimeric G protein has a transmembrane domain whereas the alpha and beta subunits are peripheral proteins If G alpha was locked in a GTP bound state, it would be bound to the effector enzyme rather than to the beta and gamma subunits. In some but not all signaling pathways, when the beta and gamma subunits are separated from alpha - the beta/gamma pair can also stimulate the activation of effectorsarrow_forwardWhy is the GTPase activity of G proteins crucial to the proper functioning of a cell? Propose a theory as to why G proteins have not evolved to catalyze GTP hydrolysis more efficiently.arrow_forward
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