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
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
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
Certain yeast cells secrete a molecule called the α factor. The purpose of this molecule is to _____.
stimulate an a yeast cell to grow toward the α cell
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
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.
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 proteomes.
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
Steroid hormones can enter a cell by simple diffusion. Therefore steroids _____.
None of the listed responses is correct.
A small molecule that specifically binds to a larger molecule is called a(n) _____.
ligand
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
G-protein-linked receptors _____, whereas receptor tyrosine kinases _____.
are not enzymes ... have enzymatic function
Which of the following is activated when the binding of single molecules causes it to form a dimer?
receptor tyrosine kinases
The binding of a signal molecule to a ligand-gated ion channel _____.
affects the membrane potential
Nitric oxide is unusual among animal signal molecules in that it _____.
is a gas
A G protein is active when _____.
GTP is bound to it
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
What event would activate a G protein?
replacement of GDP with GTP
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?
a mutation that means Ras cannot hydrolyze GTP to GDP
The cellular response of a signal pathway that terminates at a transcription factor would be _____.
the synthesis of mRNA
Cholera develops when the bacterial toxin _____.
prevents G-protein inactivation, which leads to the continuous production of cAMP
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.
The general name for an enzyme that transfers phosphate groups from ATP to a protein is _____.
protein kinase
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?
a decrease in phosphorylated proteins in the cell
Phosphorylation _____.
can either activate or inactivate a protein
The source of phosphate for a phosphorylation cascade is _____.
ATP
Second messengers tend to be water-soluble and small. This accounts for their ability to _____.
rapidly move throughout the cell by diffusion
cAMP usually directly activates _____.
protein kinase A
A mutation in the active site of adenylyl cyclase that inactivates it would most likely lead to _____.
lower activity of protein kinase A
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.
In a typical cell, calcium ions _____.
are often concentrated within the endoplasmic reticulum
In a typical cell, calcium ions _____.
None of the listed responses is correct.
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 listed responses are correct.
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
IP3 (inositol trisphosphate) is produced as a result of _____.
the cleavage of a certain kind of phospholipid in the plasma membrane
IP3 (inositol trisphosphate) acts by _____. (
opening Ca2+ channels
Which of the following is NOT a potential source of Ca2+ that can be released into the cytoplasm?
lysosomes
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
In the inherited disorder Wiskott-Aldrich syndrome, _____.
a multifunctional relay protein involved with the proliferation of immune cells is defective
In liver cells, epinephrine stimulates the breakdown of glycogen. As the signal-transduction pathway progresses, _____.
the signal is amplified
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
Apoptosis _____.
is essential for normal development of the nervous system
Which of the following statements is/are correct?
All of the listed responses are correct.
