question

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

answer

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

question

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 _____.

answer

local regulator

question

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

answer

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

question

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

answer

stimulate an a yeast cell to grow toward the α cell

question

Cells use different signaling strategies to achieve different goals. In hormonal signaling _____.

answer

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

question

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?

answer

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

question

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

answer

Different types of cells possess different proteomes.

question

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

answer

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

question

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

answer

None of the listed responses is correct.

question

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

answer

ligand

question

Receptors for signal molecules _____.

answer

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

question

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

answer

not all cells have cytoplasmic receptors for testosterone

question

G-protein-linked receptors _____, whereas receptor tyrosine kinases _____.

answer

are not enzymes ... have enzymatic function

question

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

answer

receptor tyrosine kinases

question

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

answer

affects the membrane potential

question

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

answer

is a gas

question

A G protein is active when _____.

answer

GTP is bound to it

question

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 _____.

answer

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

question

What event would activate a G protein?

answer

replacement of GDP with GTP

question

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 would you expect to see in a cancer cell that has mutated Ras present?

answer

a mutation that means Ras cannot hydrolyze GTP to GDP

question

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

answer

the synthesis of mRNA

question

Cholera develops when the bacterial toxin _____.

answer

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

question

What did Sutherland discover about glycogen metabolism in liver cells?

answer

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

question

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

answer

protein kinase

question

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

answer

a decrease in phosphorylated proteins in the cell

question

Phosphorylation _____.

answer

can either activate or inactivate a protein

question

The source of phosphate for a phosphorylation cascade is _____.

answer

ATP

question

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

answer

rapidly move throughout the cell by diffusion

question

cAMP usually directly activates _____.

answer

protein kinase A

question

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

answer

lower activity of protein kinase A

question

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?

answer

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

question

In a typical cell, calcium ions _____.

answer

are often concentrated within the endoplasmic reticulum

question

In a typical cell, calcium ions _____.

answer

None of the listed responses is correct.

question

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.

answer

All of the listed responses are correct.

question

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

answer

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

question

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

answer

the cleavage of a certain kind of phospholipid in the plasma membrane

question

IP3 (inositol trisphosphate) acts by _____. (

answer

opening Ca2+ channels

question

Which of the following is NOT a potential source of Ca2+ that can be released into the cytoplasm?

answer

lysosomes

question

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?

answer

cyclic AMP

question

In the inherited disorder Wiskott-Aldrich syndrome, _____.

answer

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

question

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

answer

the signal is amplified

question

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

answer

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

question

Apoptosis _____.

answer

is essential for normal development of the nervous system

question

Which of the following statements is/are correct?

answer

All of the listed responses are correct.

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