Cell Signaling

(Q006) Which of the following statements is TRUE? Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior. To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol. A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response. 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.

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

(Q012) The length of time a G protein will signal is determined by the activity of phosphatases that turn off G proteins by dephosphorylating Gα. activity of phosphatases that turn GTP into GDP. degradation of the G protein after Gα separates from Gβγ. GTPase activity of Gα.

GTPase activity of Gα.

(Q028) Akt promotes the survival of many cells by affecting the activity of Bad and Bcl2. Which of the following statements is FALSE? In the presence of a survival signal, Akt is phosphorylated. In the absence of a survival signal, Bad inhibits the cell-death inhibitor protein Bcl2. In the presence of a survival signal, the cell-death inhibitory protein Bcl2 is active. In the absence of a survival signal, Bad is phosphorylated.

In the absence of a survival signal, Bad is phosphorylated.

(Q007) Which of the following statements about molecular switches is FALSE? Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off. Protein kinases transfer the terminal phosphate from ATP onto a protein. Serine/threonine kinases are the most common types of protein kinase. A GTP-binding protein exchanges its bound GDP for GTP to become activated.

Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off.

(Q004) The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000 -dalton protein. You add purified QGF to different types of cells to determine its effect on these cells. When you add QGF to heart muscle cells, you observe an increase in cell contraction. When you add it to fibroblasts, they undergo cell division. When you add it to nerve cells, they die. When you add it to glial cells, you do not see any effect on cell division or survival. Given these observations, which of the following statements is most likely to be TRUE? Because it acts on so many diverse cell types, QGF probably diffuses across the plasma membrane into the cytoplasm of these cells. Glial cells do not have a receptor for QGF. QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed. Heart muscle cells, fibroblasts, and nerve cells must all have the same receptor for QGF.

QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed.

(Q010) The following happens when a G-protein-coupled receptor activates a G protein. The β subunit exchanges its bound GDP for GTP. The GDP bound to the α subunit is phosphorylated to form bound GTP. The α subunit exchanges its bound GDP for GTP. It activates the α subunit and inactivates the βγ complex.

The α subunit exchanges its bound GDP for GTP.

(Q001) When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a neurotransmitter. hormone. dissolved gas. scaffold.

hormone

(Q030) All members of the nuclear receptor family are cell-surface receptors. do not undergo conformational changes. are found only in the cytoplasm. interact with signal molecules that diffuse through the plasma membrane.

interact with signal molecules that diffuse through the plasma membrane.

(Q008) Foreign substances like nicotine, morphine, and menthol exert their initial effects by killing cells immediately, exerting their physiological effects by causing cell death. diffusing through cell plasma membranes and binding to transcription factors to change gene expression. interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus. removing cell-surface receptors from the plasma membrane.

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