Mel Bio Test 11

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Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because Athey always lead to the same cellular response.
B.they amplify the original signal manyfold.
Cthe number of molecules used is small and fixed.
D.they are species specific.
E.they counter the harmful effects of phosphatases.

B

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?
A.. intracellular receptor
B. G protein-coupled receptor
C. receptor tyrosine kinase
D. phosphorylated receptor tyrosine kinase dimer
E. ligand-gated ion channel

E

The activation of receptor tyrosine kinases is characterized by
A. GTP hydrolysis.
B. channel protein shape change.
C. dimerization and IP3 binding.
D. dimerization and phosphorylation.
E. a phosphorylation cascade.

D

Lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because
A. only target cells retain the appropriate DNA segments.
B. intracellular receptors are present only in target cells.
C. only target cells possess the cytosolic enzymes that transduce the testosterone.
D. only in target cells is testosterone able to initiate the phosphorylation cascade leading to activated transcription factor.
E. most cells lack the Y chromosome required.

B

Consider this pathway: epinephrine- (G protein-coupled receptor)- protein adenylyl cyclase- cAMP. Identify the second messenger.
A. adenylyl cyclase
B. G protein-coupled receptor
C. cAMP
D. GTP
E. G protein

C

Apoptosis involves all but which of the following?
A. lysis of the cell
B. digestion of cellular contents by scavenger cells
C. cell-signaling pathways
D. fragmentation of the DNA
E. activation of cellular enzymes

A

Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells?
A. Receptor studies indicated that epinephrine was a ligand.
B. Glycogen breakdown was observed only when epinephrine was administered to intact cells.
C. Enzymatic activity was proportional to the amount of calcium added to a cell-free extract.
D. Epinephrine was known to have different effects on different types of cells.
E. Glycogen breakdown was observed when epinephrine and glycogen phosphorylase were combined.

B

Protein phosphorylation is commonly involved with all of the following except
A. enzyme activation.
B. activation of protein kinase molecules.
C. activation of G protein-coupled receptors.
D. regulation of transcription by extracellular signaling molecules.
E. activation of receptor tyrosine kinases.

C

Select the statement that correctly distinguishes between relay proteins and second messengers in signal transduction pathways.
A. Relay proteins are the "first messengers," the extracellular signaling molecules that bind to the membrane receptor. The signal transduction pathways are then formed by the second messengers, which are the relay molecules that respond to the first messengers.
B. Signal transduction pathways are multistep pathways in which relay proteins and second messengers alternate.
C. Signal transduction pathways are multistep pathways that include relay proteins and small, nonprotein, water-soluble molecules or ions called second messengers.

C

Which statement correctly distinguishes the roles of protein kinases and protein phosphatases in signal transduction pathways?
A. Protein kinases activate enzymes by phosphorylating or adding phosphate groups to them. Protein phosphatases dephosphorylate or remove phosphate groups from enzymes, including protein kinases.
B. Protein kinases are involved in signal transduction in unicellular eukaryotes such as yeast. Protein phosphatases are involved in signal transduction in multicellular eukaryotes.
C. Protein kinases are more critical than protein phosphatases to signal transduction enzymes.

A

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.
A. Viagra increases the rate of hydrolysis of cGMP to GMP.
B. Viagra inhibits the hydrolysis of GMP to GMP.
C. Viagra prevents the formation of cGMP.

B

The cholera bacterium Vibrio cholerae produces an enzyme toxin that chemically modifies a G protein involved in regulating salt and water secretion in intestinal cells. Stuck in its active form, the modified G protein stimulates the production of a high concentration of cAMP, which causes the intestinal cells to secrete large amounts of salts into the intestines, with water following by osmosis. An infected person quickly develops profuse diarrhea and if left untreated can soon die from the loss of water and salts. What is the basic effect of the cholera toxin?
A.The basic effect of the cholera toxin is loss of specificity of the response of intestinal cells to a signaling molecule.
B. The basic effect of the cholera toxin is premature termination of a signaling pathway.
C. The basic effect of the cholera toxin is signal amplification.

C

Select all that apply.What are the functions of signal transduction pathways?
A. Signal transduction pathways amplify the effect of a signal molecule.
B. Signal transduction pathways allow different types of cells to respond differently to the same signal molecule.
C. Signal transduction pathways convert a signal on a cell's surface to a specific cellular response.

ABC

Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because
A. they counter the harmful effects of phosphatases.
B. they amplify the original signal manyfold.
C. they always lead to the same cellular response.
D. they are species specific.
E. the number of molecules used is small and fixed.

B

Which of the following provides molecular evidence that signal transduction pathways evolved early in the history of life?
A. Receptor molecules have been identified in preparations of fossilized organisms billions of years old.
B. Simple forms of life, such as prokaryotic cells, utilize cell signaling.
C. The pathways in primitive organisms, such as bacteria, are short, whereas those in advanced forms, such as mammals, are long.
D. Cell signaling is observed in organisms that do not utilize sexual reproduction.
E. The molecular details of cell signaling are quite similar in organisms whose last common ancestor was a billion years ago.

E

Which of the following is a substance that acts at a long distance from the site at which it is secreted?
A. synaptic signal
B. paracrine signal
C. hormone
D. neurotransmitter
E. local regulator

C

What is most likely to happen to an animal's target cells that lack receptors for local regulators?
A. Hormones would not be able to interact with target cells.
B. They could divide but never reach full size.
C. They might compensate by receiving nutrients via a factor.
D. They could develop normally in response to neurotransmitters instead.
E. They might not be able to multiply in response to growth factors from nearby cells.

E

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?
A. endocrine signaling
B. synaptic signaling
C. autocrine signaling
D. hormonal signaling
E. paracrine signaling

E

In the formation of biofilms, such as those forming on unbrushed teeth, cell signaling serves which function?
A. digestion of unwanted parasite populations
B. aggregation of bacteria that can cause cavities
C. secretion of substances that inhibit foreign bacteria
D. secretion of apoptotic signals
E. formation of mating complexes

B

In which of the following ways do plant hormones differ from hormones in animals?
A. Plant hormones interact primarily with intracellular receptors.
B. Plant hormones may travel in air or through vascular systems.
C. Animal hormones are primarily for mating and embryonic development.
D. Plant hormones are synthesized from two or more distinct molecules.
E. Animal hormones are found in much greater concentration.

B

When a neuron responds to a particular neurotransmitter by opening gated ion channels, the neurotransmitter is serving as which part of the signal pathway?
A. transducer
B. endocrine molecule
C. receptor
D. signal molecule
E. relay molecule

D

The following question is based on the figure below:Which of the following types of signaling is represented in the figure?
A. synaptic
B. hormonal
C. paracrine
D. autocrine
E. long distance

A

The following question is based on the figure below:In the figure, the dots in the space between the two structures represent which of the following?
A. hormones
B. receptor molecules
C. signal transducers
D. pheromones
E. neurotransmitters

E

In yeast signal transduction, a yeast cell
A. produces signal molecules that change the cell itself, allowing it to interact with another cell.
B. must physically and directly interact with another yeast cell.
C. secretes molecules that result in responses by other yeast cells.
D. produces response molecules that diffuse to other yeast cells.
E. mates with another cell, after which the new cells secrete hybrid signals.

C

To what does the term "ligand" refer in cell biology?
A. the target cell of a signal molecule
B. the change in shape that occurs when a signaling molecule binds to its receptor
C. any small molecule that can bind in a specific manner to a larger one
D. the bond that forms between a signaling molecule and its receptor
E. a molecule that can occupy a receptor site while not activating the receptor

C

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?
A. growth factor receptors
B. enhancers
C. DNA polymerases
D. nucleosomes
E. transcription factors

E

What is the function of tyrosine-kinase receptors?
A. enzymatic degrading of GTP to GDP
B. enzymatic phosphorylation of tyrosine in the receptor protein
C. enzymatic hydrolyzing of the signaling molecule shortly after its arrival
D. allowing specific ions to enter the cell after ligand binding
E. binding to nonpolar signaling molecules such as nitric oxide or the steroid hormones

B

Which of the following is true of transcription factors?
A. They initiate the epinephrine response in animal cells.
B. They transcribe ATP into cAMP.
C. They regulate the synthesis of lipids in the cytoplasm.
D. They control gene expression.
E. They regulate the synthesis of DNA in response to a signal.

D

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?
A. ligand-gated ion channels
B. receptor tyrosine kinases
C. G protein-coupled receptors
D. steroid receptors

B

Use this description to answer the following question.A major group of G protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others.
Where would you expect to find the carboxyl end?
A. between the membrane layers
B. at the exterior surface
C. at the cytosol surface
D. connected with the loop at H5 and H6

C

Use this description to answer the following question.
A major group of G protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others.
The coupled G protein most likely interacts with this receptor
A. along the exterior margin.
B. along the interior margin.
C. at the loop between H5 and H6.
D. at the NH3 end.
E. at the COO- end.

C

Testosterone functions inside a cell by
A. acting as a signal receptor that activates tyrosine kinases.
B. coordinating a phosphorylation cascade that increases spermatogenesis.
C. acting as a steroid signal receptor that activates ion channel proteins.
D. binding with a receptor protein that enters the nucleus and activates specific genes.
E. becoming a second messenger that inhibits nitric oxide.

D

If an animal cell suddenly lost the ability to produce GTP, what might happen to its signaling system?
A. It could activate only the epinephrine system.
B. It would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane.
C. It would be able to carry out reception and transduction but would not be able to respond to a signal.
D. It would use ATP instead of GTP to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane.
E. It would employ a transduction pathway directly from an external messenger.

B

When protein membrane receptors are activated, what usually happens?
A. The receptors open and close in response to protein signals.
B. A change occurs on only one membrane surface: exterior or interior.
C. The receptor preferentially binds with lipid or glycolipid signal molecules.
D. A change occurs in intracellular ion concentration.
E. The receptor changes conformation after binding with signal polypeptides.

E

Particular receptor tyrosine kinases (RTKs) that promote excessive cell division are found at high levels on various cancer cells. A protein, Herceptin, has been found to bind to an RTK known as HER2. HER2 is sometimes excessive in cancer cells. This information can now be utilized in breast cancer treatment if which of the following is true?
A. If the patient's cancer cells have excessive levels of HER2.
B. If HER2, administered by injection, causes cell division.
C. If the patient has RTKs only in cancer cells.
D. If Herceptin is found in the breast lymph nodes of the patient.
E. If the patient's genome codes for the HER2 receptor.

A

Which of the following is true of steroid receptors?
A. The receptor may be inside the nuclear membrane.
B. The receptor molecules are free to move in and out of most organelles.
C. The receptor molecules are themselves lipids or glycolipids.
D. The unbound steroid receptors are quickly recycled by lysosomes.
E. The concentration of steroid receptors must be relatively high in most cells.

A

Which of the following are among the most common second messengers?
A. kinase and phosphate groups
B. G proteins and GTP
C. kinase and phosphatase
D. GTP and GDP
E. calcium ion and cAMP

E

Which of the following sequences is correct?
A. binding of a signaling molecule to its receptor → G protein activation → adenylyl cyclase activation → cAMP production → protein phosphorylation
B. diffusion of a signaling molecule across the plasma membrane → binding of the signaling molecule to its receptor → movement of the signaling molecule-receptor complex into the nucleus → transcription
C. binding of a growth factor to its receptor → phosphorylation cascade → activation of transcription factor → transcription
D. binding of a signaling molecule to its receptor → G protein activation → phospholipase C activation → IP3 production → increase in cytoplasmic calcium concentration
E. All of the choices are correct.

E

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?
A. loss of transcription factors
B. blockage of the synaptic signal
C. low oxygen concentration around the cell
D. insufficient ATP levels in the cytoplasm
E. low levels of protein kinase in the cell

D

An inhibitor of phosphodiesterase activity would have which of the following effects?
A. prolong the effect of epinephrine by maintaining elevated cAMP levels in the cytoplasm
B. decrease the amount of cAMP in the cytoplasm
C. block the response of epinephrine
D. block the activation of G proteins in response to epinephrine binding to its receptor
E. block the activation of protein kinase A

A

Adenylyl cyclase has the opposite effect of which of the following?
A. GTPase
B. phosphodiesterase
C. protein phosphatase
D. protein kinase
E. phosphorylase

B

Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who has recently consumed coffee would have increased levels of
A. GTP.
B. phosphorylated proteins.
C. cAMP.
D. adenylyl cyclase.
E. activated G proteins.

C

If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound
A. that increases phosphorylase activity.
B. to block G protein activity in liver cells.
C. that activates epinephrine receptors.
D.that increases cAMP production in liver cells.
E. that keeps sugar molecules from crossing the plasma membrane of liver cells.

B

If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound
A. that increases phosphodiesterase activity.
B. to stimulate G protein activity in liver cells.
C. that mimics epinephrine and can bind to the epinephrine receptor.
D. that stimulates cAMP production in liver cells.
E. that does any of the above.

A

An inhibitor of which of the following could be used to block the release of calcium from the endoplasmic reticulum?
A. adenylyl cyclase
B. tyrosine kinases
C. phospholipase C
D. serine/threonine kinases
E. phosphodiesterase

C

Which of the following statements is true of signal molecules?
A. When signal molecules first bind to receptor tyrosine kinases, the receptors phosphorylate a number of nearby molecules.
B. In most cases, signal molecules interact with the cell at the plasma membrane and then enter the cell and eventually the nucleus.
C. In response to some G protein-mediated signals, a special type of lipid molecule associated with the plasma membrane is cleaved to form IP3 and calcium.
D. Toxins such as those that cause botulism and cholera interfere with the ability of activated G proteins to hydrolyze GTP to GDP, resulting in phosphodiesterase activity in the absence of an appropriate signal molecule.
E. Protein kinase A activation is one possible result of signal molecules binding to G protein-coupled receptors.

E

Which of the following is a correct association?
A. phosphorylase activity and the catabolism of glucose
B. kinase activity and the addition of a tyrosine
C. adenylyl cyclase activity and the conversion of cAMP to AMP
D. phosphodiesterase activity and the removal of phosphate groups
E. GTPase activity and hydrolysis of GTP to GDP

E

Which of the following amino acids are most frequently phosphorylated by protein kinases in the cytoplasm during signal transduction?
A. glycine and histidine
B. tyrosines
C. serine and threonine
D. glycine and glutamic acid
E. Any of the 20 amino acids are equally phosphorylated.

c

The function of phosphatases in signal transduction is best described as to
A. inactivate protein kinases and turn off the signal transduction.
B. amplify the second messengers such as cAMP.
C. prevent a protein kinase from being reused when there is another extracellular signal.
D. move the phosphate group of the transduction pathway to the next molecule of a series.
E. amplify the transduction signal so it affects multiple transducers.

A

What explains the increased concentration of in the ER?
A. Calcium levels in the blood or other body fluids are extremely low.
B. Calcium concentration is kept low in the cytoplasm because of its high usage level.
C. Calcium cannot enter the plasma membrane through ion channels.
D. Calcium ions are actively imported from the cytoplasm into the ER.
E. The CA+ ions are recycled from other molecules in the ER.

D

The toxin of Vibrio cholerae causes profuse diarrhea because it
A. modifies a G protein involved in regulating salt and water secretion.
B. modifies calmodulin and activates a cascade of protein kinases.
C. signals IP3 to act as a second messenger for the release of calcium.
D. binds with adenylyl cyclase and triggers the formation of cAMP.
E. decreases the cytosolic concentration of calcium ions, making the cells hypotonic.

A

Which of the following would be inhibited by a drug that specifically blocks the addition of phosphate groups to proteins?
A. G protein-coupled receptor binding
B. ligand-gated ion channel signaling
C. receptor tyrosine kinase activity
D. adenylyl cyclase activity
E phosphatase activity

C

Viagra causes dilation of blood vessels and increased blood flow to the penis, facilitating erection. Viagra acts by inhibiting
A. the hydrolysis of cGMP to GMP.
B. the removal of GMP from the cell.
C. the phosphorylation of GDP.
D. the dephosphorylation of cGMP.
E. the hydrolysis of GTP to GDP.

A

In general, a signal transmitted via phosphorylation of a series of proteins
A. allows target cells to change their shape and therefore their activity.
B. requires binding of a hormone to a cytosol receptor.
C. requires phosphorylase activity.
D. brings a conformational change to each protein.
E. cannot occur in yeasts because they lack protein phosphatases.

D

Which of the following most likely would be an immediate result of growth factor binding to its receptor?
A. phosphorylase activity
B. protein kinase activity
C. protein phosphatase activity
D. adenylyl cyclase activity
E. GTPase activity

B

In which of the following ways could signal transduction most probably be explored in research to treat cancer?
A. increase in the concentration of phosphodiesterases in order to produce more AMP
B. alteration of protein kinases in cell cycle regulation in order to slow cancer growth
C. removal of serine/threonine phosphate acceptors from transduction pathways in colon pre-cancerous growths
D. expansion of the role of transduction inhibitors in the cells before they give rise to cancer
E. increase in calcium ion uptake into the cytoplasm in order to modulate the effects of environmental carcinogens

B

Sutherland discovered that the signaling molecule epinephrine:
A. elevates cytosolic concentrations of cyclic AMP.
B. interacts directly with glycogen phosphorylase.
C. causes lower blood glucose by binding to liver cells.
D. brings about a decrease in levels of cAMP as a result of bypassing the plasma membrane.
E. interacts with insulin inside muscle cells.

A

For the greatest advantage of multiple steps in a transduction pathway is:
A. Each individual step can remove excess phosphate groups from the cytoplasm.
B. Having multiple steps provides for greater possible amplification of a signal.
C. Each step can be activated by several G proteins simultaneously.
D. Many of the steps can be used in multiple pathways.
E. Having multiple steps in a pathway requires the least amount of ATP.

B

Why are there often so many steps between the original signal event and the cell's response?
A. Long, highly specific pathways minimize the possibility that a relay molecule accidentally could activate a pathway leading to a secondary response.
B. The accumulation of genetic mutations over time has added redundant steps to the pathway.
C. Each transduction is a checkpoint.
D. Lengthy pathways provide the opportunity for the initial pathway molecules to recycle back to inactive forms should additional signaling molecules be present.
E. Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses.

E

Why can a signaling molecule cause different responses in different cells?
A. Different cells possess different enzymes, which modify the signaling molecule into different molecules after it has arrived.
B. Different cells have membrane receptors that bind to different sides of the signaling molecule.
C. The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor.
D. The transduction pathway in cells has a variable length.
E. All of the above are correct.

C

A drug designed to inhibit the response of cells to testosterone would almost certainly result in which of the following?
A. a decrease in G protein activity
B. an increase in receptor tyrosine kinase activity
C. an increase in cytosolic calcium concentration
D. a decrease in transcriptional activity of certain genes
E. lower cytoplasmic levels of cAMP

D

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?
A. Estrogen is produced in very large concentration and therefore diffuses widely.
B. Estrogen is kept away from the surface of any cells not able to bind it at the surface.
C. Estrogen has specific receptors inside several cell types, but each cell responds in the same way to its binding.
D. Estrogen binds to specific receptors inside many kinds of cells, each of which have different responses to its binding.
E. The subcomponents of estrogen, when metabolized, can influence cell response.

D

What are scaffolding proteins?
A. microtubular protein arrays that allow lipid-soluble hormones to get from the cell membrane to the nuclear pores
B. ladderlike proteins that allow receptor-ligand complexes to climb through cells from one position to another
C. large molecules to which several relay proteins attach to facilitate cascade effects
D. relay proteins that orient receptors and their ligands in appropriate directions to facilitate their complexing
E. proteins that can reach into the nucleus of a cell to affect transcription

C

GTPase activity is important in the regulation of signal transduction because it
A. phosphorylates protein kinases.
B. converts cGMP to GTP.
C. hydrolyzes GTP to GDP thus shutting down the pathway.
D. decreases the amount of G protein in the membrane.
E. increases the available concentration of phosphate.

C

What is apoptosis?
A. a way to stimulate transcription
B. a type of second messenger
C. a type of membrane receptor
D. controlled cell suicide
E. a metabolic step in blood clotting

D

Why has C. elegans proven to be a useful model for understanding apoptosis?
A. The animal has as many genes as complex organisms, but finding those responsible is easier than in a more complex organism.
B. While the organism ages, its cells die progressively until the whole organism is dead.
C. All of its genes are constantly being expressed so all of its proteins are available from each cell.
D. The nematode undergoes a fixed and easy-to-visualize number of apoptotic events during its normal development.
E. This plant has a long-studied aging mechanism that has made understanding its death just a last stage.

D

Why is apoptosis potentially threatening to the healthy "neighbors" of a dying cell?
A. Released cellular energy would interfere with the neighbors' energy budget.
B. Neighboring cells would activate immunological responses.
C. Cell death would usually spread from one cell to the next via paracrine signals.
D. Lysosomal enzymes exiting the dying cell would damage surrounding cells.
E. Bits of membrane from the dying cell could merge with neighbors and bring in foreign receptors.

D

In C. elegans, ced-9 prevents apoptosis in a normal cell in which of the following ways?
A. Ced-9 remains inactive until it is signaled by ced-3 and other caspases.
B. Ced-9 cleaves to produce ced-3 and ced-4.
C. It prevents the caspase activity of ced-3 and ced-4.
D. Ced-9 prevents blebbing by its action on the cell membrane.
E. Ced-9 enters the nucleus and activates apoptotic genes.

C

Which of the following describes the events of apoptosis?
A. The cell's DNA and organelles become fragmented, the cell dies, and it is phagocytized.
B. The cell dies, and the presence of its fragmented contents stimulates nearby cells to divide.
C. The cell's DNA and organelles become fragmented, the cell shrinks and forms blebs, and the cell's parts are packaged in vesicles that are digested by specialized cells.
D. The cell's nucleus and organelles are lysed, and the cell enlarges and bursts.
E. The cell dies, it is lysed, its organelles are phagocytized, and its contents are recycled.

C

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. excess skin loss
B. activation of a developmental pathway found in the worm but not in humans
C. formation of molecular pores in the mitochondrial outer membrane
D. neurodegeneration
E. a form of cancer in which there is insufficient apoptosis

E

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?
A. cAMP levels change very frequently.
B. Their lower hormone concentrations elicit a lesser response.
C. ATP production decreases.
D. Enzymatic activity declines.
E. Growth factor ligands do not bind as efficiently to receptors.

E

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