Becker's World of the Cell (9th Edition)
9th Edition
ISBN: 9780321934925
Author: Jeff Hardin, Gregory Paul Bertoni
Publisher: PEARSON
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Chapter 23, Problem 23.3PS
Heterotrimeric and Monomeric G Proteins. G protein–coupled receptors interact with heterotrimeric G proteins to activate them.
(a) Upon binding to the receptor, the Gβγ subunit catalyzes GDP/GTP exchange by the Gα subunit. How is this similar to the activation of Ras by a receptor tyrosine kinase?
(b) What similarities are there at the molecular level between how cells regulate the rate of GTP hydrolysis by the catalytically active portion of a heterotrimeric G protein and by Ras?
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Chapter 23 Solutions
Becker's World of the Cell (9th Edition)
Ch. 23 - One effect of the hormone insulin is to cause...Ch. 23 - You are working on a new species of sea urchin...Ch. 23 - The Ca2+ concentration in unstimulated cells is...Ch. 23 - Prob. 23.3CCCh. 23 - Prob. 23.4CCCh. 23 - Prob. 23.5CCCh. 23 - Chemical Signals and Second Messengers. Fill in...Ch. 23 - QUANTITATIVE Pure agony. Agonists are drugs that...Ch. 23 - Heterotrimeric and Monomeric G Proteins. G...Ch. 23 - Calcium Chelators and Ionophores. In addition to...
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- Signal-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_forwardRTKs are receptors made of an extracellular ligand binding domain and an intracellular kinase domain (see image). Insulin binds to its RTK Insulin receptor, causing an increase in glucose absorption and storage in liver cells. EGF binds to its own RTK, EGFR and promotes cell growth through the Ras pathway. a) Explain why the same type of tyrosine kinase in two RTKs can lead to very different cellular responses. Give an example of potential cellular outputs for each of these two RTKs.arrow_forwardFor the protein Calmodulin-1: 1) this protein have any secondary, tertiary and/or quaternary structures present? 2) Are there any molecular additions to this protein that are not amino acids?For both questions, can you explain if so, where specifically? The protein Calmodulin-1 is stated to have the molecular function of signaling receptor binding which is interrelated with the biological function of calcium-mediated signaling. Can you explain this relationship?arrow_forward
- 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.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_forwardRGS proteins accelerate the GAP activity of Gα subunits. What is the direct result of this GAP activity? - hydrolysis of GTP, resulting in a GDP-bound Gα - phosphorylation of GDP to GTP, resulting in a GTP-bound Gα - an exchange of GTP for GDP bound to Gα - an exchange of GDP for GTP bound to Gαarrow_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_forwardSome protein kinases are inactive unless they are phosphorylated on key serine or threonine residues. In some cases, active enzymes can be generated by mutating these serine or threonine residues to aspartate. Explain.arrow_forwardSuppose that Protein J which is a hypothetical protein kinase receptor was determined to be related to the progression of cancer through its activation. It was also determined that the protein exists in the active and inactive forms. The said active form is highly similar to the Protein K's conformation. Ligands A, B, and C, which are lead inhibitor compounds, were optimized to inhibit Protein J. The affinities of the ligands are shown in the table. Kp values Active Protein J Inactive Protein J Protein K Ligand A 10 mM 20 nM 5 mM Ligand B 20 nM 10 mM 15 nM Ligand C 20 nM 15 nM 15 nM Question: a. Which of the ligands, based on the table, has the highest specificity in binding to the target Protein J?arrow_forward
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