Cell Signaling

Figure 9.15 shows how normal signaling works with a Ras protein acting downstream of a receptor kinase. You examine a cell line in which Ras is always activated even in the absence of a signaling molecule. This causes constant activation of the kinases in the MAP kinase pathway. Which of the following conditions would be MOST likely to turn off this abnormally active signaling pathway?

the addition of a drug that prevents the final kinase from interacting with its target protein in the nucleus

Determine which statements below accurately describe how defects in Ras would impact signaling. (Select all that apply.)

-A Ras protein that exchanges GDP for GTP more easily than normal would increase signaling. -A Ras protein that cannot hydrolyze GTP to GDP would increase signaling.

Which of the following is/are true about G proteins? (Select all that apply.)

-G proteins release GDP and bind GTP when associated with an activated receptor. -Some G proteins are composed of three subunits. -G proteins become deactivated when bound GTP is hydrolyzed to GDP.

How does the Ras mutant described in the article differ from normal Ras? (Select all that apply.)

-There is a small pocket present on the mutant protein that is different than the normal protein. -The primary structure of the normal and mutant proteins differs by one amino acid.

A researcher is studying a G protein-coupled receptor in eukaryotic cells. In one group of cells, he notices that even though a ligand can bind to its G protein-coupled receptor, nothing happens. Why could this happen?

-These cells might carry mutations in the downstream signaling pathway associated with this G protein-coupled receptor. -The G protein-coupled receptor might carry a mutation that affects the receptor's transmembrane portion. -The G protein-coupled receptor might carry a mutation, so that it fails to undergo a conformational change upon the binding of its ligand.

Which of the following is considered a proto-oncogene?

-a gene encoding a protein kinase -a gene encoding a G-protein -a gene encoding a growth factor -a gene encoding a cell-surface receptor

Second messengers:

-amplify the effects of the signal. -play a role in activation of intracellular signal transduction. -are small intracellular molecules that participate in signal transduction. -are removed in order to terminate a cellular signaling response.

Ligand binding to a receptor kinase results in:

-binding of cytoplasmic signaling molecules. -phosphorylation of the cytoplasmic domain of the receptor. -receptor dimerization.

The extent and duration of a cellular response to a signal depend on the:

-level of expression of the signal transduction proteins. -concentration of the signaling molecule in the vicinity of the receptor. -binding affinity of the receptor to the signaling molecule. -level of expression of proteins that terminate the response.

Which of the following CORRECTLY pairs enzymes that activate and terminate the same step in a signaling event? (Select all that apply.)

-protein kinase (activates) and phosphatase (terminates) -adenylyl cyclase (activates) and phosphodiesterase (terminates)

Which type of receptor undergoes a conformational change upon activation? (Select all that apply.)9.6

-receptor kinase -ligand-gated ion channel -intracellular receptor -G protein-coupled receptor

Tumor suppressors oppose oncogenes by:

-slowing cell division. -instructing defective cells to die. -repairing mutations. -blocking the action of an oncogene.

If two signaling pathways are activated simultaneously:

-they may strengthen each other. -one may inhibit the other. -they may inhibit each other.

Based on the information in the article, predict which types of cancers might be effectively treated with the new drug.

Cancers with the specific mutation in Ras that have the specific cysteine abnormally present.

According to Figure 9.6, what is a key difference between cell signaling by a cell-surface receptor and cell signaling by an intracellular receptor?

Cell-surface receptors bind polar signaling molecules; intracellular receptors bind nonpolar signaling molecules.

Choose the statements that accurately describe the impact of the new drug on cells with normal Ras and cell with the mutant Ras described in the article.

In cells with the mutant Ras, adding the new drug would decrease signaling through the cell proliferation-signaling pathway.

What role does the small G protein Ras play in signaling?

It acts as a molecular switch in signal transduction pathways.

What does a ligand-gated channel do?

It allows ions to move across the plasma membrane.

Which of the following statements regarding tumor suppressors is TRUE?

Mutations affecting tumor suppressors can contribute to the development of cancers.

Which of the following receptors becomes phosphorylated when it is bound by its signaling molecule ligand?

Receptor kinases

Based on the article "Drug strategy blocks leading driver of cancer", to what form of Ras does the new drug bind?

The new drug only binds to the mutant form of Ras.

You create a cell that has a mutation in a receptor protein that binds a signaling molecule, which is also produced by the same cell. When you overexpress the signaling molecule produced by this cell, nothing happens. What is defective in this cell?

autocrine signaling

Many scientists use chemical inhibitors to interfere with normal signaling pathways within eukaryotic cells. If such inhibitors are large, nonpolar molecules, what is the likely method of action of these chemical inhibitors?

These chemical inhibitors likely bind to receptors and interfere with receptor activation or signal-receptor binding.

A proto-oncogene is a "normal" gene that, if mutated, can become an oncogene and lead to a cell becoming cancerous. T or F

True

What is the end result of activating the MAP kinase pathway?

a change in gene expression

Which of the following events are listed in the CORRECT order?

adenylyl cyclase catalyzes the formation of cAMP, which activates protein kinase A

Which of the following is a type of cell communication where the signaling molecule is released by the same cell that responds to the signal?

autocrine

A newly discovered signaling molecule that binds to a G protein-coupled receptor is being studied by using cells maintained in cell culture. Preliminary results show that the binding of this new ligand causes the activation of adenylyl cyclase. In the next part of this study, a non-hydrolyzable version of GTP (a form of GTP that cannot be converted to GDP) is added to the cell culture dishes and is taken up by the cells. Which of the following would you expect to observe?

increased cAMP, increased protein kinase A activity

In order for a G protein to be active:

the alpha subunit must bind GTP, and the beta and gamma subunits must separate from the alpha subunit.

The ability of a specific tissue or organ to respond to the presence of a hormone is dependent on:

the presence of the appropriate receptors on the cells of the target tissue or organ.

Phosphatases are responsible for the inactivation of:

the protein that is activated by protein kinase A.