(09) Cell Signaling

a Ras molecule that has no GTPase activity

A number of mutations have been described in G proteins, such as Ras, that have profound effects on their activity. For example, some mutations greatly increase the affinity of the G protein for GDP, making it very difficult for GDP to be exchanged for GTP. Other mutations prevent the hydrolysis of GTP to GDP. Which of the following scenarios would still result in a proliferation signal via the kinase cascade in the absence of ligand binding to its receptor kinase? A) a continuously active Ras protein and an inactive MAP kinase pathway B) a continuously inactive MAP kinase pathway and an inactive Ras protein C) a continuously active receptor and an inactive MAP kinase pathway D) a continuously activated receptor in the absence of ligand E) a Ras molecule that has no GTPase activity

the cells are in close proximity

Cell signaling between two nerve cells can be thought of as an example of paracrine signaling because: A) a receptor is activated B) a signaling molecule (neurotransmitter) is released) C) the cells are in close proximity D) the responding cell releases more of the signaling molecule (neurotransmitter)

Phosphatases remove phosphate groups.

How do mitogen-activated protein (MAP) kinases become inactive? A) Receptor kinases move apart in the membrane. B) Ras hydrolyzes GTP to GDP. C) Ligand diffuses away from the ligand-binding site. D) Phosphatases remove phosphate groups.

peripheral membrane protein

How is a G protein classified?

The G protein would be active and signaling, despite the lack of ligand.

How would the signal of a G protein-coupled receptor, without ligand, be affected if you made a G protein that converted GDP to GTP on its own without needing to be activated by the G protein-coupled receptor? A) The G protein would be active and signaling, despite the lack of ligand. B) The signal wouldn't be affected; there is no ligand, thus no signal. C) The G protein would be active but unable to signal due to the lack of ligand. D) The signal wouldn't be affected; the ligand would be unable to bind due to the conformational change.

the protein target activated by protein kinase A

In the G protein-coupled signal transduction pathway, phosphatases are responsible for the inactivation of: A) protein kinase A B) All of these choices are correct. C) adenylyl cyclase D) the alpha subunit of a G protein E) the protein target activated by protein kinase A

Delta

In the developing nervous system, ______ is the signaling molecule that results in the differentiation of glial cells.

both the binding affinity of the receptor and concentration of ligand surrounding the cell

Inactivation of a cell-surface receptor depends on: A) both the binding affinity of the receptor and concentration of ligand surrounding the cell B) the binding affinity of the receptor C) the activity of phosphatases in the cytosol D) the concentration of ligand surrounding the cell

paracrine signaling

Platelet-derived growth factor (PDGF) is a signaling molecule that functions in which type of cell signaling?

All of these choices are correct.

Ras is a type of G protein because it: A) All of these choices are correct. B) Responds to the activation of G protein-coupled receptors. C) Is only active when it binds GTP. D) Triggers the formation of cyclic AMP.

the alpha subunit of three-subunit G proteins

Ras is most similar to: A) the alpha subunit of three-subunit G proteins B) the gamma subunit of three-subunit G proteins C) the beta subunit of three-subunit G proteins D) receptor kinases E) ion channels

There would be no change in the rate of DNA uptake.

Recall from the text the example of cell communication in Streptococcus pneumoniae: The rate of DNA uptake by pneumococcal cells increases sharply when they are at high density, due to changes in gene expression brought about by signaling between cells. If the pneumococcal cells did not express receptor proteins, how would the rate of DNA uptake be affected when the cells reach high density? A) There would be a decrease in the rate of DNA uptake. B) There would be a smaller than normal increase in the rate of DNA uptake. C) There would be a larger than normal increase in the rate of DNA uptake. D) There would be no change in the rate of DNA uptake.

a sequential increase in the different components of the signal transduction pathway

Signal amplification relies on: A) increased activity of protein phosphatases B) increasing amounts of ligand as signal transduction proceeds C) a sequential increase in the different components of the signal transduction pathway D) increasing numbers of cell-surface receptors as the signal is transduced

a response by the cell

Signal transduction results in: A) termination of the signal B) a response by the cell C) a change in the conformation of the receptor protein D) production of more signal molecules

a conformational change to protein kinase A

The activation of protein kinase A by cyclic AMP binding likely occurs because of: A) the phosphorylation of protein kinase A B) a conformational change to protein kinase A C) the activity of a phosphatase D) the binding of GTP to protein kinase A

contact-dependent signaling

The differentiation of embryonic stem cells into neurons and glial cells is a consequence of which type of cell signaling?

transmembrane protein

The signaling molecule involved in contact-dependent cell signaling is a:

The alpha subunit catalyzes the hydrolysis of GTP to GDP and inorganic phosphate.

What causes the inactivation of a G protein?

All of these choices are correct.

What happens to the alpha subunit of a G protein with GDP attached? A) It re-associates with the G protein-coupled receptor. B) It no longer activates an effector protein. C) All of these choices are correct. D) It reassembles with the beta and gamma subunits.

a change in gene expression

What is the cell's likely response to ligand binding to a steroid receptor located in the nucleus? A) change in ion transport B) initiation of a signal transduction pathway C) a change in gene expression D) activation of a kinase

a conformational change in the cytoplasmic domain of the receptor

What is the very FIRST effect of ligand binding to a G protein-coupled receptor? A) the activation of an effector protein B) a conformational change in the cytoplasmic domain of the receptor C) the release of the alpha subunit of the G protein D) an exchange of GTP in place of GDP on the alpha subunit of the G protein

It would continue in the absence of ligand.

What would happen to the signaling cascade if phosphatases were nonfunctional? A) None of the other answer options is correct. B) It would stop in the absence of ligand. C) It would slow down in the absence of ligand. D) It would continue in the absence of ligand.

Adenylyl cyclase activity increases.

When a ligand binds to a G protein-coupled receptor, which of the following would you expect to happen FIRST? A) None of the other answer options is correct. B) Phosphodiesterase activity increases. C) Protein kinase activity increases. D) Adenylyl cyclase activity increases. E) The amount of cAMP in the cytoplasm increases.

adenylyl cyclase (activates) and phosphodiesterase (terminates)

Which of the following CORRECTLY pairs enzymes that activate and terminate the same step in a signaling event? (Select all that apply.) A) adenylyl cyclase (activates) and phosphodiesterase (terminates) B) protein kinase (activates) and phosphatase (terminates) C) protein kinase (activates) and phosphodiesterase (terminates) D) adenylyl cyclase (activates) and phosphatase (terminates)

All G proteins are a component of a signal-transduction pathway and associate with a G protein-coupled receptor.

Which of the following is NOT true about G proteins? A) G proteins release GDP and bind GTP when associated with an activated receptor. B) Some G proteins are composed of three subunits. C) All G proteins are a component of a signal-transduction pathway and associate with a G protein-coupled receptor. D) G proteins become deactivated when bound GTP is hydrolyzed to GDP.

All of these choices are correct.

Which of the following is TRUE about the Delta protein? A) Delta is a transmembrane protein found in embryonic brain cells. B) All of these choices are correct. C) Delta directs adjacent cells to differentiate into glial cells. D) Delta directly signals to a Notch transmembrane protein in adjacent cells. E) Delta is produced by embryonic stem cells as they differentiate into neurons in the brain.

kinase

Which type of protein adds a phosphate group to another molecule?

ligand-gated ion channel

Which type of receptor is involved in rapid responses of muscle cells and neurons?

Ras activates the MAP kinase signal transduction pathway.

Why are some mutations of Ras associated with cancer? A) Ras alters ion flow across the cell membrane. B) Ras activates the MAP kinase signal transduction pathway. C) Ras binds to growth factor receptors. D) Ras is a type of second messenger.

The receptor monomers must move together and dimerize to be activated.

Why do the functions of many receptor kinases depend on the fluid nature of the plasma membrane? A) The generation of cAMP requires a fluid membrane. B) The receptor monomers must move together and dimerize to be activated. C) Phosphorylation requires a fluid membrane. D) Binding of ligand to the receptor requires a fluid membrane.

Protein phosphatases

_______ inactivate receptor kinases.

PDGF binds to:

a receptor kinase

MAP kinase pathway

activated by activated GTP-bound Ras (a single-subunit G-protein); final activated kinase in pathway enters nucleus and phosphorylates target proteins, some turn on genes needed for cell division so cuts can heal

receptor kinases

have an extracellular portion that binds signaling molecule, intracellular portion is a kinase (transfers phosphate group from ATP to another molecule)

quorum sensing

in bacteria, when there are high concentrations of similar bacteria nearby, bacteria become permeable to DNA (horizontal gene transfer)

beta-adrenergic receptors

members of a class of GPCRs; abundant type of receptor in humans + frequent drug target; binding site forms a "basket" open to the outside w/ many molecular contacts composed of 7 transmembrane alpha helices, thru which signal is transmitted

In many signaling pathways, once a signaling molecule binds to a receptor, the receptor becomes phosphorylated. This initial phosphorylation step BEST demonstrates:

receptor activation

dimerization

single PDGF molecule binds to extracellular portion of 2 receptors, causing receptors to partner; activates cytoplasmic kinase domains of paired receptors

contact-dependent signaling in neurons

two neuronal precursors start out the same; one activates Delta (and becomes neuron), leads to Notch activation/Delta inactivation in other cell (becomes a helper cell); a sheet of precursors turns into a sheet of neurons interspersed b/w helper cells