Chapter 9

In the context of cell signaling, to what does the term ligand refer?

a signaling molecule that binds to the receptor

Which one of the answer choices would be found inside the cell and not on the cell surface?

a steroid receptor

signaling molecules (ligands)

carrier of information transmitted when signaling molecule binds to receptor

cancer is a disease of

cell division

Termination is an important step in adrenaline signaling because:

it allows organisms to respond to new stresses. it allows an appropriate level of response. it prevents an excessive response to adrenaline.

You strip off all proteins on the cell surface by using a protease (an enzyme that destroys proteins). Now, when you add a specific signaling molecule, the cell still responds.

The receptor for this signal is inside the cell, and the signaling molecule is nonpolar and can diffuse into the cell.

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.

According to the figure, 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.

In cell communication, which of these is a requirement of the responding cell?

It must express receptor proteins.

What does a ligand-gated channel do?

It allows ions to move across the plasma membrane, It opens a channel through the plasma membrane when signal molecules bind, It can be closed and restrict ion flow when signal molecules are absent.

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.

Nicotine from cigarette smoke acts as a ligand and associates with the acetylcholine receptor on specific cells in the nervous system. Nicotine eventually produces feelings of pleasure and well-being. The listed statements are descriptions of the events that happen in the cellular response to nicotine.

Nicotine binds to the transmembrane protein that normally binds the neurotransmitter acetylcholine. The acetylcholine receptor is an ion channel, and when a ligand binds, the ion channel opens. An influx of ions carries the signal to the reward areas of the brain. . The signal causes release of dopamine in the brain, which causes good feelings. Nicotine is quickly eliminated from the body (causing cravings for more cigarettes to produce good feelings).

How do mitogen-activated protein (MAP) kinases get deactivated?

Phosphatases remove phosphate groups

Why are some mutations of Ras associated with cancer?

Ras activates the MAP kinase signal transduction pathway that regulates cell division.

What is the key difference between blood serum and blood plasma that affects their ability to help fibroblasts grow in culture?

Serum contains factors released by platelets during blood clotting. Plasma is from unclotted blood and does not contain these factors.

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.

quorum sensing

The ability of bacteria to sense the presence of other bacteria via secreted chemical signals.

Of the answer choices, what is the most likely reason that paracrine signaling does not activate the cell that is producing the signaling molecule?

The cell does not have the proper receptor.

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

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.

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

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

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.

Vascular endothelial growth factor (abbreviated VEGF and pronounced "Veg-F") is a peptide signaling molecule related to platelet-derived growth factor. VEGF is important in the formation of the circulatory system because its signaling pathway causes the formation of blood vessels in developing embryos during normal development. Tumors also produce and secrete VEGF, causing nearby blood vessels to branch and grow to form new blood vessels that supply these tumors.

VEGF is a paracrine signaling molecule because it binds to receptors on nearby cells, at the site where new blood vessels are needed.

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

a conformational change to protein kinase A (PKA).

G proteins of G protein-coupled receptors are often made up of three subunits:

alpha, beta and gamma.

Streptococcus pneumoniae

bacterium that causes pneumonia, meningitis, and some kinds of arthritis and uses quorum sensing

Ligand binding to a receptor kinase results in:

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

What is the cell's likely response to ligand binding to a steroid receptor located in the nucleus?

change in gene expression

The first step following platelet-derived growth factor (PDGF) binding of the receptor is:

dimerization of the receptor.

Which signaling system involves the longest distance between release of a signaling molecule and activation of a receptor?

endocrine

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

Kohler and Lipton first discovered platelet-derived growth factor (PDGF) by observing that fibroblasts:

grew better in cell culture containing blood serum containing proteins released by platelets during clotting.

receptor proteins

molecule on the responding cell that binds to the signaling molecule

responding cell

receives information from the signaling molecule.

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

receptor activation.

four elements required for cellular communication

signaling cell, signaling molecule, receptor protein, and responding cell.

receptor activation

signaling molecule binds to receptor

Which signaling molecules would you expect to travel the longest distance in the human body?

testosterone

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

the proteins activated by protein kinase A.

signaling cell

the source of the signaling molecule

GTP binding occurs on which subunit of a G protein?

the α (alpha) subunit

If two signaling pathways are activated simultaneously:

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

Signaling molecules involved in paracrine and autocrine signaling

travel by diffusion.