Exam 16: Cell Signaling

Nuclear receptors have binding sites for a signaling molecule and a DNA sequence.How is it that the same nuclear receptor, which binds to a specific DNA sequence, can regulate different genes in different cell types?

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 Figure 16-15.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 Brainy transcription? Figure 16-15

Activated GPCRs activate G proteins by reducing the strength of binding of GDP to the α subunit of the G protein, allowing GDP to dissociate and GTP (which is present at much higher concentrations in the cell than GDP) to bind in its place.How would the activity of a G protein be affected by a mutation that reduces the affinity of the α subunit for GDP without significantly changing its affinity for GTP?

Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen, as depicted in Figure 16-16. Figure 16-16 Which of the following statements is FALSE?

You are interested in further understanding the signal transduction pathway that controls the production of Pig1, a protein important for regulating cell size.Activation of the TRK receptor leads to activation of the GTP-binding protein, Ras, which then activates a protein kinase that phosphorylates the SZE transcription factor.SZE only interacts with the nuclear transport receptor when it is phosphorylated.SZE is a gene activator for the Pig1 gene.This pathway is diagrammed in Figure 16-25. Figure 16-25 Normal cells grown under standard conditions (without ligand) are 14 μm in diameter while normal cells exposed to TRK ligand are 10.5 μm in diameter.Given this situation, which of the following conditions do you predict will more likely lead to smaller cells?

The length of time a G protein will signal is determined by the

Which of the following statements about molecular switches is FALSE?

A protein kinase can act as an integrating device in signaling if it

Figure 16-34 shows that intracellular signaling pathways can be highly interconnected. Figure 16-34 From the information in Figure 16-34, which of the following statements is FALSE?

Name the three main classes of cell-surface receptor.

Which of the following statements is FALSE?

Can signaling via a steroid hormone receptor lead to amplification of the original signal? If so, how?

The rod photoreceptors in the eye are extremely sensitive to light.The cells sense light through a signal transduction cascade involving light activation of a GPCR that activates a G protein that activates cyclic GMP phosphodiesterase.How would you expect the addition of the following drugs to affect the light-sensing ability of the rod cells? Explain your answers. A.a drug that inhibits cyclic GMP phosphodiesterase B.a drug that is a nonhydrolyzable analog of GTP

For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below.Not all words or phrases will be used; each word or phrase should be used only once. adenylyl cyclase endoplasmic reticulum nuclear average extracellular peroxisome high phospholipase C calmodulin intracellular protein kinase A colorful low protein kinase C Ca²⁺ can trigger biological effects in cells because an unstimulated cell has an extremely __________ concentration of free Ca²⁺ in the cytosol, compared with its concentration in the __________ space and in the __________ creating a steep electrochemical gradient.When Ca²⁺ enters the cytosol, it interacts with Ca²⁺-responsive proteins such as __________ which also binds diacylglycerol, and __________ which activates CaM-kinases.

For each of the following sentences, select the best word or phrase from the list below to fill in the blanks.Not all words or phrases will be used; each word or phrase should be used only once. adenylyl cyclase cholera toxin GTPase AMP diacylglycerol phosphodiesterase ATP five seven ATPase four three GDP twelve cAMP GTP two G-protein-coupled receptors (GPCRs) all have a similar structure with __________ transmembrane domains.When a GPCR binds an extracellular signal, an intracellular G protein, composed of __________ subunits, becomes activated.__________ of the G-protein subunits are tethered to the plasma membrane by short lipid tails.When unstimulated, the α subunit is bound to __________ which is exchanged for __________ on stimulation.The __________ activity of the α subunit is important for inactivating the G protein.__________ inhibits this activity of the α subunit, thereby keeping the subunit in an active state.

Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells.Which of the following statements is FALSE?

Acetylcholine acts at a GPCR on heart muscle to make the heart beat more slowly.It does so by ultimately opening K⁺ channels in the plasma membrane (as diagrammed in Figure 16-51), which decreases the cell's excitability by making it harder to depolarize the plasma membrane. Indicate whether each of the following conditions would increase or decrease the effect of acetylcholine. A.addition of a drug that stimulates the GTPase activity of the Gα subunit B.mutations in the K⁺ channel that keep it closed all the time C.modification of the Gα subunit by cholera toxin D.a mutation that decreases the affinity of the βγ complex of the G protein for the K⁺ channel E.a mutation in the acetylcholine receptor that prevents its localization on the cell surface F.adding acetylcholinesterase to the external environment of the cell

Your friend is studying mouse fur color and has isolated the GPCR responsible for determining its color, as well as the extracellular signal that activates the receptor.She finds that, on addition of the signal to pigment cells (cells that produce the pigment determining fur color), cAMP levels rise in the cell.She starts a biotech company, and the company isolates more components of the signaling pathway responsible for fur color.Using transgenic mouse technology, the company genetically engineers mice that are defective in various proteins involved in determining fur color.The company obtains the following results. • Normal mice have beige (very light brown) fur color. • Mice lacking the extracellular signal have white fur. • Mice lacking the GPCR have white fur. • Mice lacking cAMP phosphodiesterase have dark brown fur. Your friend has also made mice that are defective in the α subunit of the G protein in this signaling pathway.The defective α subunit works normally except that, once it binds GTP, it cannot hydrolyze GTP to GDP.What color do you predict that the fur of these mice will be? Why?

Figure 16-20 shows the pathway through which nitric oxide (NO) triggers smooth muscle relaxation in a blood vessel wall.Which of the following situations would lead to relaxation of the smooth muscle cells in the absence of acetylcholine? Figure 16-20

Which of the following statements is TRUE?