Chapter 9 CBIO Learning Curve

According to Figure 9.11, which of the following is NOT responsible for amplifying the signal in a cell responding to adrenaline signaling?

One adrenaline molecule can bind to and activate many receptors simultaneously.

Describe one way in which endocrine, paracrine, autocrine, and contact-dependent signaling pathways are similar to one another and one way in which they are different from one another.

One way in which the signaling pathways are similar is that the steps involved in the signaling cascade are the same (that is, receptor activation, signal transduction, response, and termination). One difference between the pathways is the distance between the signaling and responding cell. Another difference is whether the signaling molecule is released by the signaling cell (endocrine, paracrine, autocrine) or a transmembrane protein (signaling between neighboring cells).

Why do the functions of many receptor kinases depend on the fluid nature of the plasma membrane?

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

A protein on a cell surface that binds to a signaling molecule is an example of which of the following elements of cellular communication?

a receptor protein

Signal amplification relies on:

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

A chemical that binds to a cell and causes its activity to change is an example of which of the following elements of cellular communication?

a signaling molecule

Notch and Delta are both transmembrane proteins involved in cell communication in the developing nervous system of vertebrate animals. What makes Notch different from Delta?

Notch is a receptor and Delta is a signaling molecule.

What is a growth factor?

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

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

a transmembrane protein.

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

grew better in cell culture when blood serum from clotted blood was added to the growth medium instead of blood plasma from unclotted blood

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

paracrine

Explain how signals can specifically target only some cells, even if they are released into the bloodstream and come into contact with many cells.

A signal can be specific for a particular cell type because the signal only recognizes receptors with a binding site specific for that signal. These receptors are not present on every cell; different cell types express a different assortment of receptor types on their surface. In this way, only a subset of cells respond to any given signal, even if that signal is present throughout the organism.

Many diseases are the result of a problem with cell signaling. Which of the following diseases best exemplifies this fact?

A specific type of cancer, caused by a truncated receptor that becomes stuck in the activated form.

Which of the following is TRUE about the Delta protein? Delta is a transmembrane protein found in embryonic brain cells. Delta is produced by embryonic stem cells as they differentiate into neurons in the brain. Delta directs adjacent cells to differentiate into glial cells. Delta directly signals to a Notch transmembrane protein in adjacent cells.

All are correct

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

All of the above

Second messengers:

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

Compare and contrast receptors associated with polar and nonpolar signaling molecules.

Cell-surface receptors are usually transmembrane proteins with an extracellular domain, transmembrane domain, and cytoplasmic domain. They are specific for polar signaling molecules that cannot diffuse across the membrane. These polar ligands bind with the receptor outside the cell. The receptor then transmits the signal to the inside of the cell, leading to a cellular response. That response could be the activation of an enzyme or transcription of a particular gene, for example. Intracellular receptors are present inside the cell, either in the cytoplasm or in the nucleus. Their signaling molecules are typically nonpolar and can easily diffuse through the plasma membrane. Once inside the cell, the ligand binds with its receptor, causing the receptor to change shape. In the case of steroid hormones, the ligand receptor complex moves into the nucleus if it is not there already, to activate gene transcription.

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.

Explain how cells respond to external signals, even when those signals cannot enter the cell.

Cells respond to signals by means of specific transmembrane proteins called receptors that bind to the signal (ligand) by the receptor's specific ligand-binding site. The binding of the ligand to its receptor causes a conformational change in the receptor, activating it. The activated receptor transmits the signal inside the cell, generating a response. The type of ligand and receptor determine how the cell responds to the signal.

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

Molecules found in serum promote cell growth; these molecules are not found in plasma.

Which of the following types of cellular activities can be a response to cell signaling?

Gene expression patterns are changed. Cell division is triggered. Cell signals are released to communicate with other cells. Enzyme activities are changed. All of these choices are correct.

List three ways in which a signal is amplified in a G protein-coupled receptor signaling pathway.

In the example of G protein-coupled receptors, a signal is amplified in several ways. A single activated G protein coupled receptor can activate multiple G proteins. Each active G protein activates an adenylyl cyclase molecule, each of which generates a large amount of cAMP. Each cAMP molecule activates a molecule of protein kinase A (PKA). Once activated, each PKA enzyme phosphorylates and activates multiple protein targets.

What does a ligand-gated channel do?

It allows ions to move across the plasma membrane.

Describe three ways in which the response of a cell to a signal can be terminated.

Response of a cell to a signal can be terminated at a variety of levels. The receptor itself could change its conformation to the inactive form, the protein interacting with the intracellular portion of the receptor could become inactivated (perhaps due to dephosphorylation), or any of the downstream proteins (like cAMP or protein kinase A) could become inactivated.

List several responses a cell might have to a signaling molecule.

Several possible types of responses a cell might have to a signaling molecule are migration of the cell, activation of a particular protein, shape change of the cell itself, cell division, and cell differentiation, to name a few.

During the signal transduction process, the signal often triggers a signal transduction cascade. For example: An activated receptor activates hundreds of protein A. Each activated protein A activates hundreds of protein B and so on until a cellular response occurs. What purpose does this cascade serve?

The cascade serves to amplify the signal, so one activated receptor can have a significant response.

Name the four essential elements in cell communication.

The four essential elements in cell communication are a signaling cell, a signaling molecule, a receptor protein, and a responding cell.

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?

The mice will have fewer glia compared to their normal counterparts.

Signaling molecules involved in paracrine and autocrine signaling:

travel by diffusion.

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 protein, how would the rate of DNA uptake be affected when the cells reach high density?

There would be no change 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 and interfere with receptor activation or signal-receptor binding.

Which of the following is not a true statement about receptors that are localized to the nucleus?

They bind polar ligands.

Name the steps that occur when a signal binds to a receptor on a responding cell.

When a signal binds a receptor on a responding cell, the following steps typically occur: receptor activation, signal transduction, response, and termination.

Describe three different responses of a cell-surface receptor on binding a signaling molecule and undergoing a conformational change.

When a signaling molecule binds to and changes the shape of a receptor, G protein-coupled receptors bind and activate G proteins, receptor kinases phosphorylate each other, and ion channels open or close.

A researcher is evaluating the role of a growth factor during embryonic development. She notices that this factor functions in both neural development and limb development. How is that possible? (The effects of the growth factor may be concentration-dependent. The effects of the growth factor may be dependent on location. The growth factor may result in the transcription of different genes depending on cell type. The growth factor may be signaling through different transduction pathways.)

all are correct

If two signaling pathways are activated simultaneously: (they may inhibit each other. they may strengthen each other. one may inhibit the other.)

all are correct

Which of the following CORRECTLY lists the types of cellular communication from shortest to longest distance traveled by the signaling molecule to reach its responding cell?

autocrine, paracrine, endocrine

Which of the following types of cell signaling generally occurs between cells that are distant from each other?

endocrine

Cell signaling over a long distance is known as:

endocrine signaling.

The presence of excess EGF receptors can result in:

excessive cell division.

Given that 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 in Fig. 9.5, which method of culturing resulted in the greatest number of fibroblast cells on day 6? Click to view full size.

fibroblasts cultured with serum

Types of steroids include:

insect molting hormones. glucocorticoids that regulate blood glucose levels. sex hormones such as estrogen and testosterone. lipid-soluble hormones derived from cholesterol. All of these choices are correct.

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

ligand-gated ion channel

According to Figure 9.14, phosphate groups play a key role in receptor kinase activation by:

providing binding sites to recruit and activate signal-transduction proteins.

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

receptor activation.

Which type of cell-surface receptor undergoes changes in phosphorylation in response to binding of its ligand?

receptor kinase

A cell that responds to an environmental condition by the release of a chemical is an example of which of the following elements of cellular communication?

signaling cell

Signaling through receptor kinases:

takes place in most eukaryotic organisms.

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

testosterone

GTP binding occurs on which subunit of a G protein?

the alpha subunit

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

the signal is either similar in structure to a ligand used by eukaryotes, or this signaling pathway is utilized by both prokaryotes and eukaryotes.

What is the function of adenylyl cyclase?

to form cyclic AMP