Q9

You are interested in cell-size regulation and discover that signaling through a GPCR called ERC1 is important in controlling cell size in embryonic rat cells. The G protein downstream of ERC1 activates adenylyl cyclase, which ultimately leads to the activation of PKA. You discover that cells that lack ERC1 are 15% smaller than normal cells, while cells that express a mutant, constitutively activated version of PKA are 15% larger than normal cells. Given these results, which of the following treatments to embryonic rat cells should lead to smaller cells? A) Addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive B) Addition of a drug that prevents GTP hydrolysis by Gα C) Addition of a drug that activates adenylyl cyclase D) Addition of a drug that mimics the ligand of ERC1

A) Addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive

Which of the following mechanisms is not directly involved in inactivating an activated RTK? A) Dephosphorylation by serine/threonine phosphatases B) Dephosphorylation by protein tyrosine phosphatases C) Removal of the RTK from the plasma membrane by endocytosis D) Digestion of the RTK in lysosomes

A) Dephosphorylation by serine/threonine phosphatases

Which of the following statements is true? B) To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol. A) Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior. D) Any foreign substance that binds to a receptor for a normal signal molecule will always induce the same response that is produced by that signal molecule on the same cell type. C) A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response.

A) Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.

Which of the following statements is true? B) PI 3-kinase phosphorylates a lipid in the plasma membrane. A) MAP kinase is important for phosphorylating MAP kinase kinase. D) STAT proteins phosphorylate JAK proteins, which then enter the nucleus and activate gene transcription. C) Ras becomes activated when an RTK phosphorylates its bound GDP to create GTP.

B) PI 3-kinase phosphorylates a lipid in the plasma membrane.

You are interested in how cyclic-AMP-dependent protein kinase A (PKA) functions to affect learning and memory, and you decide to study its function in the brain. It is known that, in the cells you are studying, PKA works via a signal transduction pathway like the one depicted in the figure to the right. Furthermore, it is also known that activated PKA phosphorylates the transcriptional regulator called Nerd that then activates transcription of the gene Brainy. Which situation described below will lead to an increase in Brainytranscription? D) A mutation in the gene that encodes adenylyl cyclase that renders the enzyme unable to interact with the α subunit of the G protein. B) A mutation in the nuclear import sequence of PKA from PPKKKRKV to PPAAAAAV. C) A mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive. A) A mutation in the Nerd gene that produces a protein that cannot be phosphorylated by PKA.

C) A mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive.

The following happens when a G-protein-coupled receptor activates a G protein. A) The β subunit exchanges its bound GDP for GTP. B) The GDP bound to the α subunit is phosphorylated to form bound GTP. C) The α subunit exchanges its bound GDP for GTP. D) It activates the α subunit and inactivates the βγ complex.

C) The α subunit exchanges its bound GDP for GTP.

Foreign substances like nicotine, morphine, and menthol exert their initial effects by _____. A) killing cells immediately, exerting their physiological effects by causing cell death C) interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus B) diffusing through cell plasma membranes and binding to transcription factors to change gene expression D) removing cell-surface receptors from the plasma membrane

C) interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus

Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen, as depicted in the figure to the left. Which of the following statements is false? C) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glucose available. B) A constitutively active mutant form of PKA in skeletal muscle cells would not increase the affinity of adrenaline for the adrenergic receptor. D) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available. A) A constitutively active mutant form of PKA in skeletal muscle cells would lead to a decrease in the amount of unphosphorylated phosphorylase kinase.

D) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available.

All members of the steroid hormone receptor family________________________. A) are cell surface receptors B) do not undergo conformational changes C) are found only in the cytoplasm D) interact with signal molecules that diffuse through the plasma membrane

D) interact with signal molecules that diffuse through the plasma membrane