Biology 2 Chapter 11

The source of phosphate for a phosphorylation cascade is _____.

ATP

Signal amplification is most achieved by _________.

An enzymatic cascade involving multiple protein kinases

Many human diseases, including bacterial infections, and also many medicines used to treat these diseases produce their effects by influencing which of the following?

G- Protein pathways

Botulism toxin acts by interfering with _____ function.

G-protein

A G protein is active when _____.

GTP is bound to it

Which of the following is incorrectly matched with its description?

Protein phosphatase - enzyme that transfers a phosphate group from ATP to a protein, causing a conformational change that usually activates the protein

Which of the following provides the best evidence that cell-signaling pathways evolved early in the history of life?

Signal transduction molecules found in distantly related organisms are similar

Which of the following sequences is correct?

binding of a growth factor to its receptor ® phosphorylation cascade ® activation of transcription factor ® transcription

Lipid-soluble signal molecules, such as testosterone. 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 ... released from intracellular stores

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

rapidly move throughout the cell by diffusion

Many signal transduction pathways use second messengers to ________.

relay the message from the inside of membrane membrane throughout the cytoplasm

What event would activate a G protein?

replacement of GDP with GTP

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 an α yeast cell 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 signaling molecule

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

the cleavage of PIP2

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 depolymerization 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 the 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

Phosphorylation cascades involving a series of protein kinases are useful for cellular transduction because __________.

they amplify the original signal manyfold

Signal transduction pathways benefit cells for all of the following reasons except __________.

they help cells use up phosphate generated by ATP breakdown

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

tyrosine-kinase receptors

cAMP usually directly activates _____.

protein kinase A

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

Glycogen breakdown was observed when epinephrine and glycogen phosphorylase were combined

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.

Which of the following signal molecules pass through the plasma membrane and bind to intracellular receptors that move into molecules and function to transcription factors to regulate gene expression?

Testosterone, a steroid hormone

Explain why G-protein-regulated pathways shut down rapidly in the absence of a single molecule.

The G protein is also a GTPase enzyme that hydrolyzes its bound GTP to GDP and inactivates itself. It then dissociates from the enzyme it had activated, and that enzyme returns to its original state

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.

When epinephrine binds to cardiac (heart) muscle, it speeds their contraction. When it binds to muscle cells of the small intestine, it inhibits their contraction. How can the same hormones have different effects on muscle cells?

The two types of muscle cells have different signal transduction pathways for epinephrine and thus have different cellular responses.

How do receptor tyrosine kinases transduce a signal?

They form a dimer; they phosphorylate each other's tyrosines; specific proteins bind to and are activated by these phosphorylated tyrosines

Which of the following would be used in the type of local signaling called paracrine signaling in animals?

a local regulator such as a growth factor

In the inherited disorder Wiskott-Aldrich syndrome _____.

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

What is a G protein

a protein on the cytoplasmic side of a membrane that becomes activated by a receptor protein

Amplification of a chemical signal occurs when _______.

a receptor in the plasma membrane activates several G-protein molecules while a signal molecule is bound to it

Which of the following is a similarity between G-protein-linked receptors and receptor tyrosine kinases?

a-helix regions of the receptor that span the plasma membrane

a. What determines whether a cell is a target for a particular signal molecule? b. What determines whether a single molecule binds to a membrane-surface receptor or an intracellular receptor?

a. A target cell has a protein receptor that is specific for that signal. b. signals that bind to surface receptors are large, polar, and/or ionic. These hydrophilic molecules cannot pass through the membrane. Intracellular signals are small or hydrophobic and can move through the lipid membrane.

How do the following mechanisms or molecules maintain a cells ability to respond to fresh signals? a. reversible binding of signal molecules b. GTPase activity of G protein c. phosphodiesterase d. protein phosphatases

a. Signal molecules reversibly bind to receptors, and when they leave a receptor, the receptor reverts to its inactive form. The concentration of signaling molecules influences how many are bound at any time. b. Activated G proteins are inactivated when the GTPase portion of the protein converts GTP to GDP c. Phosphodiesterase converts cAMP to AMP, thus dampening out this second messenger. d. Protein phosphatases remove the phosphate groups from activated proteins. The balance of active protein kinases an active phosphatases regulates activity of many proteins.

a. What does a protein kinase do? b. What does a protein phosphatase do? c. What is a phosphorylation cascade?

a. Transfers a phosphate group from ATP to a protein; adding a charged phosphate group causes a conformation change that usually activates the protein. b. Removes a phosphate group from a protein, usually inactivating the protein. c. A series of protein kinase relay molecules that are sequentially phosphorylated.

a. Do plant cells communicate using hormones? b. If so, how do these hormones travel between secreting cells and target cells?

a. yes b. In plants, hormones (often called growth regulators) may reach their target cells by traveling through vessels, through sells via plasmodesmata, or even through the air as a gas.

Protein phosphorylation is commonly involved with all of the following except _______.

activation of G-protein-linked receptors

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

affects the membrane potential

During the transduction of a signal, one molecule or ion may be closely associated with the activity of another. Select the pair that is correctly combined.

all of the above

G-protein-linked receptors _____; whereas tyrosine-kinase receptors _____.

are not enzymes ... have enzymatic function

In a typical cell, calcium ions _____.

are often concentrated within the endoplasmic reticulum

Consider this pathway: epinephrine -> G-protein linked receptor -> G protein -> adenylyl cyclase -> cAMP -> Identify the second messenger

cAMP

Receptors for signal molecules _____.

can be found as part of the plasma membrane or found within the cytoplasm

Phosphorylation _____.

can either activate or inactivate a protein

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

cyclic AMP

The activation of receptor tyrosine kinases is always 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.

A signal molecule that binds to a plasma-membrane protein functions as a ________.

ligand

A small molecule that specifically binds to a larger molecule is called a(n) _____.

ligand

Binding of a signal molecule to which type of receptor leads directly to a change in the distribution of anions and/or cations 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(n) _____.

local regulator

Which of the following is not a potential source of Ca2+ for the cytosol?

lysosomes

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

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

Which of the following can activate protein by transferring a phosphate group to it?

protein kinase