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Using the yeast signal transduction pathways, both types of mating cells release the mating factors. These factors bind to specific receptors on the correct cells,
which induce changes in the cells that lead to cell fusion.
What is most likely to happen to an animal's target cells that lack receptors for local regulators?
They might not be able to multiply in response to growth factors from nearby cells.
Which of the following is a likely explanation of why natural selection favored the evolution of signals for sexual reproduction?
Even in the simplest organisms, sexual reproduction required several coordinated responses by cells.
Which of the following is characterized by a cell releasing a signal molecule into the environment, followed by a number of cells in the immediate vicinity responding?
paracrine signaling
In the formation of biofilms, such as those forming on unbrushed teeth, cell signaling serves which function?
aggregation of bacteria that can cause cavities
In yeast signal transduction, the yeast cells
secrete molecules that result in response by other yeast cells.
In which of the following ways do plant hormones differ from hormones in animals?
 Plant hormones may travel in air or through vascular systems.
In an experiment to track the movement of growth factor molecules from secretion to the point of receptor binding in a particular species of mammal, a student found a 20-fold reduction in mm traveled when in the presence of an adrenal hormone. This is in part attributable to which of the following?
The growth factor is a paracrine signal.
When a neuron responds to a particular neurotransmitter by opening gated ion channels, the neurotransmitter is serving as which part of the signal pathway?
signal molecule
Of the following, a receptor protein in a membrane that recognizes a chemical signal is most similar to
the active site of an allosteric enzyme that binds to a specific substrate.
Which of the following is true for the signaling system in an animal cell that lacks the ability to produce GTP?
It would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane.
Testosterone functions inside a cell by
binding with a receptor protein that enters the nucleus and activates specific genes.
Which of the following is true of transcription factors?
They control gene expression.
One of the major categories of receptors in the plasma membrane reacts by forming dimers, adding phosphate groups, and then activating relay proteins. Which type does this?
receptor tyrosine kinases
Because most receptors are membrane proteins, which of the following is usually true?
They change their conformation after binding with signal polypeptides.
Since steroid receptors are located intracellularly, which of the following is true?
The steroid/receptor complex can cross the nuclear membrane.
Receptor tyrosine kinases (RTKs) are found at high levels on various cancer cells. A protein, Herceptin, has been found to bind to an RTK known as HER2. This information can now be utilized in breast cancer treatment if which of the following is true?
If the patient's cancer cells have detectable HER2.
The receptors for a group of signaling molecules known as growth factors are often
receptor tyrosine kinases.
In general, a signal transmitted via phosphorylation of a series of proteins
 brings a conformational change to each protein.
Sutherland discovered that epinephrine signals
elevation of cytosolic concentrations of cyclic AMP.
Which of the following is the best explanation for the inability of a specific animal cell to reduce the Ca2+ concentration in its cytosol compared with the extracellular fluid?
insufficient ATP levels in the cytoplasm
The toxin of Vibrio cholerae causes profuse diarrhea because it
modifies a G protein involved in regulating salt and water secretion.
Which of the following would be inhibited by a drug that specifically blocks the addition of phosphate groups to proteins?
receptor tyrosine kinase activity
Which of the following most likely would be an immediate result of growth factor binding to its receptor?
protein kinase activity
 An inhibitor of phosphodiesterase activity would have which of the following effects?
prolong the effect of epinephrine by maintaining elevated cAMP levels in the cytoplasm
Adenylyl cyclase has the opposite effect of which of the following?
Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who has recently consumed coffee would have increased levels of
If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound
to block G protein activity in liver cells.
If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound
that increases phosphodiesterase activity.
An inhibitor of which of the following could be used to block the release of calcium from the endoplasmic reticulum?
phospholipase C
Which of the following statements is true of signal molecules?
Protein kinase A activation is one possible result of signal molecules binding to G protein-coupled receptors.
Which of the following is a correct association?
GTPase activity and hydrolysis of GTP to GDP
One inhibitor of cGMP is Viagra. It provides a signal that leads to dilation of blood vessels and increase of blood in the penis, facilitating erection. Since cGMP is inhibited, the signal is prolonged. The original signal that is now inhibited would have
hydrolyzed cGMP to GMP
Which of the following is the best explanation for the fact that most transduction pathways have multiple steps?
Multiple steps provide for greater possible amplification of a signal.
Which of the following amino acids are most frequently phosphorylated by protein kinases in the cytoplasm during signal transduction?
serine and threonine
The function of phosphatases in signal transduction is best described as to
inactivate protein kinases and turn off the signal transduction.
What explains the increased concentration of Ca++ in the ER?
 Calcium ions are actively imported from the cytoplasm into the ER.
In which of the following ways could signal transduction most probably be explored in research to treat cancer?
alteration of protein kinases in cell cycle regulation in order to slow cancer growth
A drug designed to inhibit the response of cells to testosterone would almost certainly result in which of the following?
a decrease in transcriptional activity of certain genes
At puberty, an adolescent female body changes in both structure and function of several organ systems, primarily under the influence of changing concentrations of estrogens and other steroid hormones. How can one hormone, such as estrogen, mediate so many effects?
Estrogen binds to specific receptors inside many kinds of cells, each of which have different responses to its binding.
What are scaffolding proteins?
large molecules to which several relay proteins attach to facilitate cascade effects
The termination phase of cell signaling requires which of the following?
incompatibility of the binding of the signal molecule to the receptor
GTPase activity is involved in the regulation of signal transduction because it
hydrolyzes GTP binding to G protein.
Why has C. elegans proven to be a useful model for understanding apoptosis?
The nematode undergoes a fixed and easy-to-visualize number of apoptotic events during its normal development.
Which of the following describes the events of apoptosis?
Its DNA and organelles are fragmented, the cell shrinks and forms blebs, and the cell self-digests.
If an adult person has a faulty version of the human analog to ced-4 of the nematode, which of the following is most likely to result?
a form of cancer in which there is insufficient apoptosis
Why is apoptosis potentially threatening to the healthy "neighbors" of a dying cell?
Lysosomal enzymes exiting the dying cell would damage surrounding cells.
In C. elegans, ced-9 prevents apoptosis in a normal cell in which of the following ways?
It prevents the caspase activity of ced-3 and ced-4.
In research on aging (both cellular aging and organismal aging), it has been found that aged cells do not progress through the cell cycle as they had previously. Which of the following would provide evidence that this is related to cell signaling?
Growth factor ligands do not bind as efficiently to receptors.
Where do apoptotic signals come from?
all of the above
The human population's life expectancy has increased significantly but seems to have an upper limit. Which of the following might be described as an ecological consequence of passing that upper limit by regulating cell death?
an increase in the total population of humans on the planet
Which of the following types of signaling is represented in the figure?
In the figure, the dots in the space between the two structures represent which of the following?
Where would you expect to find the carboxyl end?
at the cytosol surface
) The coupled G protein most likely interacts with this receptor
at the loop between H5 and H6.
If you wish to design an experiment to block the G protein-coupled receptor interaction, the block would preferentially affect which of the following?
the amino acid sequence in the binding site for the G protein
When an excess of the ligand (hormone) is poured through the column after the receptor binding step, what do you expect will occur?
The ligand will cause the receptor to be displaced from the beads and eluted out.
This method of affinity chromatography would be expected to collect which of the following?
molecules of purified receptor
The description above illustrates which of the following?
Just because a drug acts on one type of receptor does not mean that it will act on another type.
The use of beta 2 antagonist drugs may be useful in asthma because they may
dilate the bronchioles by relaxing their smooth muscle.
Beta 2 antagonist drugs might also be used most effectively for which of the following?
increasing low blood pressure
Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because
they amplify the original signal manyfold.
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
The activation of receptor tyrosine kinases is characterized by
dimerization and phosphorylation.
Lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because
intracellular receptors are present only in target cells.
Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP. Identify the second messenger.
Apoptosis involves all but which of the following?
lysis of the cell
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.
Protein phosphorylation is commonly involved with all of the following except
activation of G protein-coupled receptors.