Chapter 11 Biology

A mutation in the active site of adenylyl cyclase that inactivates it would most likely lead to __________.

lower activity of protein kinase A

Cholera develops when the bacterial toxin __________.

prevents G-protein inactivation, which leads to the continuous production of cAMP

The general name for an enzyme that transfers phosphate groups from ATP to a protein is __________.

protein kinase

The molecule cAMP usually directly activates __________.

protein kinase A

Second messengers tend to be water-soluble and small. This accounts for their ability to __________.

rapidly move throughout the cell by diffusion

What event would activate a G protein?

replacement of GDP with GTP

Which of the following statements best describes a key aspect of a G protein signaling pathway?

A G protein bound is active when bound to GTP.

The source of phosphate for a phosphorylation cascade is __________.

ATP

Which of the following statements is correct?

All of the listed responses are correct. -Some apoptotic signals come from mitochondria. -Some apoptotic signals originate from outside a cell. -Some apoptotic signals come from the nucleus, when DNA has suffered irreparable damage. -Some apoptotic signals come from the endoplasmic reticulum when excessive protein misfolding occurs.

During the transduction of a signal, one molecule or ion may be closely associated with the activity of another. Which of the following pairs correctly combines two associated molecules?

All of the listed responses are correct. -cAMP, protein kinase A -Calcium, IP3 -cAMP, adenylyl cyclase

Different types of cells can respond differently to the same signaling molecule. Which of the following explains this apparent paradox?

Different types of cells possess different proteins.

A G protein is active when __________.

GTP is bound to it

Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells?

Glycogen breakdown was observed only when epinephrine was administered to intact cells.

Which of the following statements about calcium ions in a typical cell is true?

In a typical cell, calcium ions are often concentrated within the endoplasmic reticulum.

Which of the following is activated when the binding of single molecules causes it to form a dimer?

Receptor tyrosine kinases

Protein phosphorylation is commonly involved with all of the following except

activation of G protein-coupled receptors.

The general name for an enzyme that transfers phosphate groups from ATP to a protein is

protein kinase

The __________ the higher ________ concentration is washed away.

signal is perceived and disappears once; salt

A signal transduction pathway is initiated when a _____ binds to a receptor.

signal molecule

ATPgammaS is a form of ATP that cannot be hydrolyzed by enzymes. If this compound were introduced to cells so that it replaced the normal ATP present in the cell, which of the following would you predict?

A decrease in phosphorylated proteins in the cell

Ras, a small G protein located at the plasma membrane, is often mutated in different types of cancer. Ras normally signals to a cell that it should divide. Cancer cells divide uncontrollably. Which of the following changes to Ras could explain uncontrolled division in a cancer cell that has mutated Ras present?

A mutation that means Ras cannot hydrolyze GTP to GDP

Which of the following statements about apoptosis is true?

Apoptosis is essential for normal development of the nervous system.

What did Sutherland discover about glycogen metabolism in liver cells?

The hormone epinephrine binds to a specific receptor on the plasma membrane of the liver cell.

What role does a transcription factor play in a signal transduction pathway?

By binding to DNA it triggers the transcription of a specific gene.

Many G protein-coupled receptors contain seven transmembrane α-helical domains. If the amino terminus of such a protein is located on the extracellular side of the membrane, where would a coupled G protein most likely interact with this receptor?

at the loop between helix 5 and helix 6

In eukaryotic cells, which of the following is a second messenger that is produced as a response to an external signal such as a hormone?

Cyclic AMP

Which of these is NOT correct?

Cyclic AMP binds to calmodulin. (Calcium binds to calmodulin)

A toxin that inhibits the production of GTP would interfere with the function of a signal transduction pathway that is initiated by the binding of a signal molecule to _____ receptors.

G-protein-linked

Epinephrine acts as a signal molecule that attaches to _____ proteins.

G-protein-linked receptor

Select the correct molecule that is the main product of the Calvin cycle.

G3P

Which of the following statements best describes the function of the α factor secreted by yeast cells?

It binds to receptors on α cells to stimulate mating between a cells and α cells.

How does the toxin of Vibrio cholerae cause profuse diarrhea?

It modifies a G protein involved in regulating salt and water secretion.

When steroid hormones enter a cell by simple diffusion, they can be said to do what in terms of concentration?

None of the listed responses is correct. (Simple diffusion must occur down a gradient, and as the molecule moving must pass through the membrane, that molecule must be nonpolar; no membrane protein is required for passive diffusion.)

Testosterone and estrogen are lipid-soluble signal molecules that cross the plasma membrane by simple diffusion. If these molecules can enter all cells, why do only specific cells respond to their presence?

Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell's nucleus.

_____ catalyzes the production of _____, which then opens an ion channel that releases _____ into the cell's cytoplasm.

Phospholipase C ... IP3 .... Ca2+

Which of the following statements describes a likely effect of a drug that inhibits testosterone binding to its receptor in human cells?

The expression of certain genes would increase or decrease.

Domoic acid is a neurotoxin produced by some species of alga. Domoic acid binds to the kainate receptor on neurons in parts of the brain. The kainate receptor facilitates the movement of calcium into the cell. Excess domoic acid-induced stimulation of the neural kainate receptors causes neural damage and short-term memory loss. Based on this, which of the following is likely true?

The kainate receptor is a ligand-gated ion channel, and domoic acid is a ligand.

Which of the following statements best describes the effect of a mutation that alters the structure of the a factor so that it no longer binds to the corresponding receptor on α cells?

The α cells will fail to initiate the shape changes necessary for mating.

What role do phosphatases play in signal transduction pathways?

They inactivate protein kinases to turn off signal transduction.

Cyclic GMP, or cGMP, acts as a signaling molecule whose effects include relaxation of smooth muscle cells in artery walls. In the penis, this signaling pathway and the resulting dilation of blood vessels leads to an erection. Select the correct statement about the effect of Viagra on this signaling pathway.

Viagra inhibits the hydrolysis of cGMP to GMP. (Viagra inhibits the hydrolysis of cGMP to GMP, thus prolonging the signal. Because Viagra leads to dilation of blood vessels, it increases blood flow to the penis, optimizing physiological conditions for penile erections.)

In the inherited disorder Wiskott-Aldrich syndrome, __________.

a multifunctional relay protein involved with the proliferation of immune cells is defective

The binding of a signal molecule to a ligand-gated ion channel __________.

affects the membrane potential

A protein kinase activating many other protein kinases is an example of _____.

amplification

G-protein-coupled receptors __________, whereas receptor tyrosine kinases __________.

are not enzymes; have enzymatic function

Many G protein-coupled receptors contain seven transmembrane α-helical domains. If the amino terminus of such a protein is located on the extracellular side of the membrane, where would you expect to find the carboxyl terminus of the protein?

at the cytosolic surface of the plasma membrane

A drug could inhibit the release of glucose from liver cells by having which of the following effects on the liver cells?

blocking G protein activity

Consider the following pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP Which of the following molecules serves as the second messenger in this pathway?

cAMP

Consider this pathway:epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP. Identify the second messenger.

cAMP

Which of these is activated by calcium ions?

calmodulin

Phosphorylation __________.

can either activate or inactivate a protein

Which of these acts as a second messenger?

cyclic AMP

The activation of receptor tyrosine kinases is characterized by

dimerization and phosphorylation.

Steroid hormones can enter a cell by simple diffusion. Therefore, steroids __________.

do not initiate cell signaling by interacting with a receptor in the plasma membrane

Calcium ions that act as second messengers are stored in _____.

endoplasmic reticula

The cleavage of glycogen by glycogen phosphorylase releases _____.

glucose-1-phosphate

The presence of _______ triggers a GPCR-based signaling pathway, involving many steps, signal amplification, and possibly ___________.

glutamate; second messengers

Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect only target cells because

intracellular receptors are present only in target cells.

Nitric oxide is unusual among animal signal molecules in that it __________.

is a gas

A difference between the mechanisms of cAMP and Ca2+ in signal transduction is that cAMP __________ and Ca2+ __________.

is synthesized by an enzyme in response to a signal; is released from intracellular stores

Which of the following statements best describes scaffolding proteins?

large molecules to which several relay proteins attach to facilitate cascade effects

Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?

ligand-gated ion channel

When a platelet contacts a damaged blood vessel, it is stimulated to release thromboxane A2. Thromboxane A2 in turn stimulates vascular spasm and attracts additional platelets to the injured site. In this example, thromboxane A2 is acting as a __________.

local regulator

A mutation in the active site of adenylyl cyclase that inactivates it would most likely lead to

lower activity of protein kinase A

Apoptosis involves all but which of the following?

lysis of the cell (Apoptosis includes: -fragmentation of the DNA -activation of cellular enzymes -cell-signaling pathways -digestion of cellular contents by scavenger cells)

Receptors for signal molecules __________.

may be found embedded in the plasma membrane or found within the cytoplasm or nucleus

Testosterone does not affect all cells of the body because __________.

not all cells have cytoplasmic receptors for testosterone

IP3 (inositol trisphosphate) acts by __________.

opening Ca2+ channels

A type of localized signaling in which a cell secretes a signal molecule that affects neighboring cells is best described as which of the following?

paracrine signaling

An inhibitor of which of the following enzymes could be used to block the release of calcium from the endoplasmic reticulum?

phospholipase C

The presence of ________ on the tongue causes _________ to enter the cell.

salt; NA+

Because activated proteins and _______ persist, the _________ the chips themselves are washed away

second messengers; taste lingers longer even after

Cells use different signaling strategies to achieve different goals. In hormonal signaling, __________.

specialized cells release hormone molecules into the circulatory system, permitting distant cells to be affected

Certain yeast cells secrete a molecule called the α factor. The purpose of this molecule is to __________.

stimulate cells of the opposite mating type, a yeast cells, to grow toward the α cell

If a modified form of GTP that cannot be enzymatically converted to GDP were added to a culture of cells, the likely result would be __________.

that the activated G proteins would remain locked in the "on" position, transmitting signal even in the absence of a signaling molecule

IP3 (inositol trisphosphate) is produced as a result of __________.

the cleavage of a specific phospholipid in the plasma membrane

In liver cells, epinephrine stimulates the breakdown of glycogen. As the signal-transduction pathway progresses, __________.

the signal is amplified

Early work on signal transduction and glycogen metabolism by Sutherland indicated that __________.

the signal molecule did not interact directly with the cytosolic enzyme but required an intact plasma membrane before the enzyme could be activated

Evidence that cell signaling evolved early in the history of life comes from __________.

the similarity of cell-signaling mechanisms in organisms that have a very distant common ancestor

The cellular response of a signal pathway that terminates at a transcription factor would be __________.

the synthesis of mRNA

Cells of the gastrointestinal (GI) tract and cells of the heart respond differently to epinephrine because __________.

there are differences in the proteins found in the two types of cells

Dioxin, produced as a by-product of various industrial chemical processes, is suspected of contributing to the development of cancer and birth defects in animals and humans. It apparently acts by entering cells by simple diffusion and binding to proteins in the cytoplasm, then altering the pattern of gene expression. Which of the following are likely to be the cytoplasmic proteins to which dioxin binds?

transcription factors (Explanation: Steroid hormone receptors located in the cytoplasm could be bound by dioxin, just as they are bound by the steroids that diffuse into the cell. Once bound by dioxin, the cytoplasmic receptor⁄dioxin complexes could move into the nucleus, where they may act as transcription factors, instigating the synthesis of mRNA.)