BIOS 1700 Ch. 9

Which change to the adrenaline signaling pathway could cause a weaker than normal response to the presence of adrenaline in the heart?

Increase the ability of G protein alpha to convert GTP to GDP and an inorganic phosphate

Normal heart cells beat more strongly when they are exposed to adrenaline. When adrenaline is removed, normal heart cells return to their normal beat strength within a few minutes. A new type of mutant heart cells has gained a function in one part of the signaling process causing that part of the process to stay in the "on" state even if the signal has been removed. These cells continue to beat strongly for hours after a single brief exposure to adrenaline. Which step in the adrenaline signaling pathway could be stuck in the "on" state in the mutant cells?

the activation of the receptor when adrenaline binds the signal transduction process activated by the receptor the enzymes activated by the response that cause stronger beats

Which of the following could lead to a prolonged increase in heart rate, even in the absence of an external signal? Choose all that apply.

-An inability of a G-protein to hydrolyze GTP -An inability to inactivate protein kinase A

In the example of adrenaline signaling, which steps represent an amplification of the signal?

Activated receptor activates G proteins, activated adenylyl cyclase produces cAMP, active protein kinase A phosphorylates target proteins

In the example of adrenaline signaling used in the animation, suppose each amplification step produces hundredfold active molecules. How many total modified protein target molecules result from a single activated signal receptor?

1,000,000

Arrange the events in the stimulation of heart muscle in order from earliest (1) to latest (5). Note that this question does not list every step in the pathway, but the steps presented should be arranged in order.

1. Activation of G-proteins 2. Activation of adenylyl cyclase 3. Conversion of ATP into cyclic AMP 4. Activation of protein kinase A 5. Phosphorylation of proteins that induce contraction in muscle cells

In the example of adrenaline signaling used in the animation, suppose each amplification step produces hundredfold active molecules. A signaling pathway resulting from a single activated signal receptor results in the consumption of _______ molecules of GTP and _______ molecules of ATP.

100; 1,010,000

Which of the following statements best summarizes the function of G protein-coupled receptors?

A signal present on the outside of the cell leads to a change on the inside of the cell

The ligand for a G protein‑coupled receptor is added to cells, but they exhibit no cellular response. After some tests, you identify ATP levels are lower than normal but GTP levels are not lower than normal. Which process(es) are likely to be affected by this? Select all that apply.

Activation of adenylyl cyclase and activation of protein kinase A

Which of the following steps does not result in an amplification of the signal information?

Activation of adenylyl cyclase by active G protein

The primary advantage of a signaling cascade is that it:

Allows a large intracellular response from a small number of extracellular signal molecules

A G protein‑coupled receptor has been activated by ligand binding. Which component activates the target protein?

Alpha G protein

What's the difference between blood serum and blood plasma?

Blood serum is the liquid portion of blood that has been allowed to clot, and blood plasma is the liquid portion of blood that has not been allowed to clot.

Which statement is true regarding the graph in Experiment 1? -Cells grown in blood serum divide rapidly over the first few days and then the rate of division slows down. -Cells grown in blood plasma divide slowly over the first few days and then the rate of division increases. -Cells grown in blood plasma grow most rapidly between days 5 and 6. -Cells grown in blood serum divide rapidly throughout the experiment. -Cells grown in blood plasma grow most rapidly between days 1 and 2.

Cells grown in blood serum divide rapidly over the first few days and then the rate of division slows down.

Which statement is true regarding the graph in Experiment 2? -Cells grown in blood plasma grow most rapidly between days 5 and 6. -Cells grown in blood serum divide rapidly throughout the experiment. -Cells grown in blood plasma divide slowly over the first few days and then the rate of division increases. -Cells grown in blood serum divide rapidly over the first few days and then the rate of division slows down. -Cells grown in blood plasma grow most rapidly between days 1 and 2.

Cells grown in blood serum divide rapidly throughout the experiment.

How is the information contained in a signaling molecule received by a cell?

Depending on the nature of the signaling molecule, it may either bind to and activate a receptor protein embedded in the plasma membrane, or it may move across the plasma membrane and bind to a receptor protein in the cytoplasm.

In a follow-up experiment, researchers took all of the platelet proteins from a sample of rat blood and created six fractions of the proteins (fractions A, B, C, D, E, F). Unfortunately, they accidentally mixed some of the fractions together when they applied the fractions to rat fibroblasts. When they looked at the growth rates of the rat fibroblasts, they saw increased growth rate with cells treated with the combined fractions ABE, BCE, and ABD. They saw decreased growth with cells treated with ACD and DEF. Finally, they saw no change in growth with cells treated with ACE, CEF, and ACF. Based on these results, which fractions likely have proteins that impact the growth of rat fibroblasts?

Fraction B has a protein that increases growth, and fraction D has a fraction that decreases growth rates.

Adrenaline stimulates an increase in heart rate by binding to:

G-protein coupled receptors on the surface of cardiac muscle cells

The alpha subunit of a G-protein is free to diffuse in the plane of the membrane when:

GDP is exchanged for GTP

Termination of the adrenaline signal begins when:

GTP bound to the G-protein alpha subunit is hydrolyzed to GDP and Pi

When a G protein-coupled receptor binds a signal molecule, it activates a G protein. The active G protein is bound to a molecule of _______, and in its active state can _________.

GTP; activate another target protein

Consider the steps in activation of a cellular response. I. Protein kinase A is activated. II. Ligand binds to G protein‑coupled receptor. III. ATP is converted into cAMP. IV. The alpha subunit of the G protein activates adenylyl cyclase. V. GDP is replaced by GTP in the G protein. In what order do the steps for the activation of a cellular response take place?

II > V > IV > III > I

If a mutation caused the G protein to become permanently bound to GTP, what result can be predicted?

It constantly signals its pathway to be "on"

The type of signaling cascade shown in the video directly affects which of these animal tissue types?

Muscle

What happens to the α (alpha) subunit of a G protein when bound GTP is replaced with GDP?

It no longer activates an effector protein. It re-associates with the G protein-coupled receptor. It reassembles with the β (beta) and γ (gamma) subunits.

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

Kinase

Predict what happens if each adenylyl cyclase enzyme is able to convert only one molecule of ATP into cAMP, reducing the amount of cAMP produced.

Not enough molecules of protein kinase A are activated and the cellular response is dampened.

G protein-coupled receptors are found:

On the cell surface

When an appropriate signal binds to a G protein-coupled receptor, what is the best description of how the information is passed across the plasma membrane?

Signal binding causes a conformational change in the cytoplasmic portion of receptor protein

What is the role of signal transduction in cell signaling?

Signal transduction connects the activation of the receptor to the cellular response.

Why don't steroid hormones bind to transmembrane cell-surface receptors?

Steroid hormones are nonpolar and therefore are able to cross the cell's plasma membrane, binding to receptors inside the cell.

Some individuals are very sensitive to adrenaline, and have adrenaline signaling pathways that are hyperactive. Which drug could reduce signaling through a hyperactive adrenaline pathway?

a drug that reduced the activity of adenylyl cyclase

What happens if the conversion of GTP into GDP by the G protein is inhibited?

The amplification reaction continues until ATP levels are too low.

One example of a cellular response to a signal is the triggering of cell division. If a mutation occurred in the gene for the signal receptor in this pathway that caused the receptor to reject binding of the signal, what response can be predicted?

The cell does not divide.

A researcher is studying a mutant eukaryotic cell that has a defect in its adrenaline signaling G protein-coupled receptor. In these cells, he notices that even though adrenaline can bind to its G protein-coupled receptor, nothing happens. What could the mutation in these cells disrupt?

The mutation might prevent G protein α subunit from binding to GTP. The mutation might prevent the activation of adenylyl cyclase. The mutation might prevent protein kinase A (PKA) from binding to cAMP. The mutation might prevent the G protein-coupled receptor from undergoing a conformational change upon the binding of its ligand.

In a follow‑up experiment, researchers took platelet growth factor proteins from chicken blood serum and they then applied those proteins to either chicken and mouse fibroblast cells (and compared their effect to that of plasma proteins from chicken or mouse). The researchers found that the chicken serum caused higher rates of growth in the chicken cells compared to the mouse cells. In addition, they found that the serum proteins caused higher growth rates in both chicken and mouse cells compared to blood plasma proteins from either species. Select the statement that best explains these results:

The platelet proteins from chickens have a stronger effect on growth factor receptors in chickens compared to growth factor receptors in mice.

When cells communicate by the signaling process, one cell produces a ______ that must be received by the ______ on or in the responding cell.

signaling molecule; signal receptor

Recall from the text in the example of cell communication in Streptococcus pneumoniae that 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 protein, how would the rate of DNA uptake be affected when the cells reach high density?

There would be no increase in the rate of DNA uptake

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 on the cell surface and interfere with receptor activation or signal-receptor binding.

Imagine that a researcher is studying the embryonic development of mice that do not express the signal molecule Delta. What will likely be true of these mice?

These mice will have fewer glial cells compared to their normal counterparts.

Which is a true statement about receptors that are localized to the nucleus?

They are synthesized in the cytosol. They bind nonpolar ligands. They carry a nuclear-localization signal. They move through a nuclear pore.

How did Kohler and Lipton measure the rate of cell division of cultured mouse fibroblasts?

They counted total number of cells at specific points in time.

Why did Kohler and Lipton start by repeating a previous experiment?

They wanted to make sure they could reproduce the results in their own laboratory. The more times the same result is obtained, the more confidence a researcher has in the results. They wanted to confirm that chicken cells behave similarly to mouse cells. They wanted a baseline for comparison to further studies involving purified platelet proteins.

A researcher introduces a large polar signaling molecule produced by bacteria to eukaryotic cells that she is culturing in the laboratory. Remarkably, she notices that the signaling of the bacteria results in an increase in eukaryotic gene expression. How is this possible?

This signal is likely similar in structure to ligands utilized by eukaryotic cells.

In Experiment 1, what treatment would have made a useful negative control? ->The researchers first confirmed earlier observations using mouse cells called fibroblasts that are easily grown in culture. They grew two sets of fibroblasts in plastic dishes. They added serum to one of the dishes and plasma to the other. They counted the number of cells in both culture dishes over time to determine the rate of cell division. Fibroblasts grown in serum divided more rapidly than those grown in plasma, as expected from earlier experiments

cells grown without blood products

The activation of protein kinase A (PKA) by cyclic AMP (cAMP) binding likely occurs because of:

a conformational change to protein kinase A (PKA).

Excess EGF receptors in breast cells can cause cancerous growth due to increased activity of the MAP kinase pathway. Which concept for an anti-cancer drug is least likely to work to reduce signaling through the pathway? -a drug that blocks the ability of Ras to convert GTP to GDP -a drug that blocks the kinase activity of the EGF receptor -a drug that blocks the ability of kinases in the pathway to enter the nucleus and activate transcription factors -a drug that blocks the ability of phosphatases to remove phosphates from kinases in the pathway

a drug that blocks the ability of Ras to convert GTP to GDP

Signal amplification relies on:

a sequential increase in the different components, wherein a single, activated component can activate many copies of the next component in the pathway.

What is a growth factor?

a signaling molecule involved in paracrine signaling a soluble molecule that can alter gene expression in a cell a small protein that influences cell growth and division

What would be a useful way to follow up on these experiments? -Examine cell growth in blood plasma compared to cell growth without the addition of plasma or serum. -Examine cell growth in blood serum compared to cell growth in blood plasma with platelet proteins. -Examine cell growth of other types of cells under the same conditions that were used in this experiment. -Examine cell growth of blood serum compared to cell growth in blood plasma with purified PDGF.

all of the above

When human breast cancer cells are genetically engineered to express excess G protein alpha or contain excess cAMP, they block cell growth by inhibiting the MAP kinase pathway. How could activation of a G protein-coupled receptor pathway block the MAP kinase pathway to block cancer cell division?

cAMP could activate phosphatases that deactivate kinases of the MAP kinase pathway.

In Experiment 2, what treatment would have made a useful negative control? ->To see if the growth‑promoting factor is released from platelets, the researchers prepared a solution of proteins made from purified platelets, added these proteins to cultured fibroblasts, and counted the number of cells over time. They found that fibroblasts grown in the presence of platelet proteins divided more rapidly than fibroblasts grown in plasma

cells grown without blood products

Which type of reaction is carried out by adenylyl cyclase?

cyclization of ATP into cAMP

A specific ligand is polar in nature. Where is the ligand‑binding portion of the receptor most likely to be located?

extracellular side of the cell membrane

Most ligands form covalent bonds with their associated receptors; these complexes are more or less permanent and can only be broken through the hydrolysis of ATP.

false

Based on the data provided in the two graphs shown, which method of culturing resulted in the greatest number of fibroblast cells on day 6? Click to view full size.

fibroblasts cultured with serum (not platelet proteins)

A ______ expresses a gene or genes that direct production of the signaling molecule, and the ______ expresses a gene or genes that direct production of the ______.

signaling cell; responding cell; receptor protein

Cellular responses that result from receptor kinase activation tend to:

involve changes in gene expression

A receptor that is inside the cell would require a ______ signal molecule that can ______ the plasma membrane.

nonpolar; pass through

Growth factors such as platelet-derived growth factor (PDGF) function in:

paracrine signaling

When blood is removed from the body, it clots. To prevent clotting, researchers can remove platelets (and cells) from the blood and treat it with anti‑clotting agents. What is produced by this treatment?

plasma

Signal molecules that are ______ usually have their corresponding receptor ______ of the cell.

polar; on the surface

Normal heart cells beat more strongly when they are exposed to adrenaline. When adrenaline is removed, normal heart cells return to their normal beat strength within a few minutes. One type of mutant heart cell has lost the function of one part of the signaling process. They respond abnormally by continuing to beat strongly for hours after a single brief exposure to adrenaline. Which step in the adrenaline signaling pathway is most likely to be disrupted in the mutant cells?

the enzymes that cause termination of the response

In the G protein-coupled signal transduction pathway, phosphatases are responsible for the inactivation of:

the proteins activated by protein kinase A.