Deck 5: Cell Signalling in Physiology

Question 1

Molecule X is some sort of chemical messenger.  Its receptor resides within the nucleus and once the receptor is bound to X,gene transcription occurs.  Molecule X might be a(n)

A)ion.
B)lipid/steroid.
C)hydrophilic protein.
D)large protein.
E)hydrophilic carbohydrate.

Answer 1

B

Question 2

Second messengers

A)are necessary for all receptor signal transduction mechanisms.
B)act in the cell cytoplasm.
C)only function as intercellular messengers.
D)always function to activate enzymes.
E)are always proteins.

Answer 2

B

Question 3

Epinephrine activates the cyclic AMP pathway in liver cells.In this example,epinephrine is a(n)________ and cAMP is a(n)________.

A)ligand;receptor
B)first messenger;hydrophobic hormone
C)second messenger;ion channel
D)first messenger;second messenger
E)enzyme;second messenger

Answer 3

D

Question 4

With regard to the action of hormones and neurotransmitters on cellular receptors,which of these describes "amplification"?

A)When the extracellular concentration of a chemical messenger reaches a very high level,it overwhelms transporter molecules and the chemical floods into the cell.
B)Only hydrophilic first-messenger molecules can activate second-messenger molecules within the cell cytosol.
C)A single first-messenger molecule activates multiple second-messenger molecules,each of which activate thousands of enzymes.
D)Some cellular receptors have such low affinity for chemical ligands that it can require a million or more molecules to activate them.

Question 5

At very low concentrations,epinephrine causes an artery to dilate.At higher concentrations epinephrine causes the same artery to constrict.How can these different effects be explained?

A)There is one type of epinephrine receptor that uses two second-messenger systems.
B)There are two types of epinephrine receptors with different affinities for epinephrine that use two different second-messenger systems.
C)There are two types of receptors for epinephrine that use the same second-messenger system.
D)At higher concentrations epinephrine can pass through the plasma membrane and directly stimulate contraction within the cell.

Question 6

The process whereby repeated exposure to a hormone can cause a decrease in the number of receptors for that hormone is called

A)competition.
B)inhibition.
C)down-regulation.
D)antagonism.
E)saturation.

Question 7

Which of these is a lipid-soluble messenger?

A)Thyroid hormone
B)Protein kinase
C)Glucose
D)Sodium
E)Cyclic AMP

Question 8

Naloxone (Narcan)is an antagonist to the opioid receptor,the same receptor to which heroin is an agonist.If both heroin and naloxone were in the bloodstream,what would the user experience?

A)A decrease in the effects of heroin
B)An increase in the effects of heroin
C)The same effects from heroin plus additional effects of naloxone
D)A new set of effects unlike those of heroin alone

Question 9

One way that cells can increase their responsiveness to an external chemical regulator is by

A)increasing the number of their transmembrane receptors by exocytosis.
B)decreasing the number of their transmembrane receptors by endocytosis.
C)uncoupling their receptors from the second message generator.
D)increasing the number of their transmembrane receptors by endocytosis.
E)mutating their extracellular receptors so that the affinity for the chemical regulator is reduced.

Question 10

Some glucose transport proteins can also bind fructose,another six-carbon monosaccharide,but not lycine,an amino acid,because transport proteins exhibit ________ for their ligands.

A)saturation
B)competition
C)affinity
D)affiliation
E)specificity

Question 11

Insulin is a protein hormone with mostly hydrophilic amino acids.Which is the most likely description of its receptor?

A)Peripheral membrane protein
B)Integral membrane protein
C)Specialized phospholipids within the membrane
D)Nucleic acids
E)Intracellular proteins

Question 12

Which of the following is NOT typically true about G proteins?

A)They act as second messengers.
B)They can be stimulatory for second-messenger production.
C)They can be inhibitory for second-messenger production.
D)They can act as transducers for activated receptors by opening or closing ion channels.

Question 13

In which situation would an injected drug be the most effective agonist for an endogenous chemical messenger?

A)The drug has a lower affinity for the messenger's receptors than the messenger does.
B)The drug achieves 50% saturation of the messenger's receptors at a lower concentration than that required by the messenger.
C)The drug does not couple to the binding site of the messenger's receptor.
D)The drug binds to an alternate binding site on the protein receptor and reduces its affinity for the endogenous chemical messenger.

Question 14

An adipose (fat)cell responds to the presence of the hormone epinephrine by increasing cytosolic cyclic AMP production,which leads to the catabolism of both glycogen and fat.What is the most likely explanation for this phenomenon?

A)Epinephrine is binding to two types of receptors in the plasma membrane.
B)The activated receptor complex stimulates production of two different second messengers.
C)Cyclic AMP directly activates enzymes that catabolize glycogen and fat.
D)Cyclic AMP-dependent protein kinase activates two kinds of enzymes.

Question 15

Which of the following is known to be a second messenger?

A)Diacylglycerol
B)Phospholipase C
C)ATP
D)Adenylyl cyclase
E)Epinephrine

Question 16

Which of the following statements is TRUE?

A)Phosphorylation by protein kinases can stimulate or inhibit the activity of effector proteins.
B)Ca²⁺ is not a second messenger.
C)Phosphodiesterase converts GMP into cGMP
D)Conversion of ATP to cAMP is a phosphorylation reaction.
E)Phospholipase C converts ATP to cAMP. 

Question 17

Researchers have found that enkephalin receptors are upregulated in cocaine addicts when compared to non-users.It is likely that the action of cocaine

A)increases enkephalin in the brain.
B)decreases enkephalin in the brain.
C)increases enkephalin's affinity for its receptor.
D)is an agonist to the enkephalin receptor.

Question 18

Which is NOT typically a step in the cAMP second-messenger system?

A)A first messenger binds to a transmembrane receptor.
B)There is dissociation of G-protein subunits.
C)An activated G-protein subunit phosphorylates cAMP-dependent protein kinase.
D)Adenylyl cyclase converts ATP into cAMP.
E)Active cAMP-dependent protein kinase phosphorylates cell proteins.

Question 19

Which of the following are ways in which binding of a chemical messenger with a cell's receptor can bring about a cellular response?

A)Opening or closing of specific ionic channels in the plasma membrane
B)Activation of an intracellular second-messenger system
C)Promoting or inhibiting the transcription of genes that code for the synthesis of cellular proteins
D)Activating or inhibiting intracellular enzymes
E)All of the choices are correct.

Question 20

Amplification during a second-messenger cascade is beneficial because amplification

A)takes small molecules and makes polymers out of them.
B)results in the production of more of the first messenger.
C)allows a cell to respond to more different hormones.
D)allows small amounts of hormones to produce large responses in target cells.

Question 21

Amplification of a second-messenger cascade can take place at which level of a signal cascade?

A)One activated receptor can activate numerous G proteins.
B)One activated G protein can activate numerous effector enzymes.
C)One active effector enzyme can catalyze numerous reactions.
D)One activated protein kinase can allosterically modulate numerous proteins.
E)All of the choices are correct.

Question 22

Competition for receptors is strictly a pharmacological phenomenon,since naturally occurring chemical messengers do not compete with each other for the same receptor site.

Question 23

Designing a drug that blocked the release of eicosanoids would be an effective therapy for both pain and inflammation.

Question 24

Which of the following might be phosphorylated in a signaling pathway?

A)G-protein coupled receptor
B)cAMP
C)Enzymes
D)Ca²⁺
E)Tyrosine residues

Question 25

Two cell types having the same type of receptor for a chemical messenger will always respond to that messenger in the same way.

Question 26

Phosphorylation is a necessary component of any enzyme activation.

Question 27

Drug Y is a drug that is used to increase the force of contraction achieved by heart muscle tissue.In the absence of the drug,epinephrine increases heart contractility through a signaling pathway that involves a receptor and cAMP.Which of the following are plausible mechanisms of action for Y?

A)Acting as an agonist on the receptor for epinephrine,a hormone that increases heart contractility
B)Increasing the expression of cAMP
C)Inhibiting phosphodiesterase activity
D)Increasing the availability of phosphodiesterase molecules
E)Decreasing the activity of cAMP-dependent protein kinase

Question 28

First messengers may bind to a membrane receptor that is an ion channel,which promotes a change in membrane polarity.

Question 29

The enzyme that catalyzes the production of cAMP from ATP is phosphodiesterase.

Question 30

Aspirin and other nonsteroidal anti-inflammatory drugs are more specific in their effects on eicosanoid synthesis than are steroidal anti-inflammatory drugs.

Question 31

Activated calmodulin functions to activate or inactivate cytosolic enzymes.

Question 32

Type 2 diabetes mellitus is a disease in which the effect insulin has on the cell is reduced,despite consistent levels of circulating insulin (in the beginning of the disease).Which of the following could possibly explain this phenomenon?

A)Upregulation of insulin receptors
B)Downregulation of insulin receptors
C)Increased affinity of insulin for its receptor
D)Decreased expression of the second messenger in the insulin pathway
E)Saturation of the insulin receptor

Question 33

Endogenous opioid molecules reduce pain sensation.Morphine,a common analgesic,is an agonist for endogenous opioid receptors.

Question 34

Cyclic AMP activates allosteric proteins.

Question 35

What is a role of calcium ions in the second-messenger cascade involving phospholipase C,diacylglycerol,and inositol trisphosphate?

A)It splits and activates G-protein subunits.
B)It binds to the endoplasmic reticulum and causes the release of inositol trisphosphate.
C)It phosphorylates cell proteins.
D)It is the first messenger that binds to the integral membrane protein receptor.
E)Along with diacylglycerol,it activates protein kinase C.

Question 36

What second messenger most directly causes calcium ions to be released from intracellular stores?

A)Diacylglycerol
B)Adenylyl cyclase
C)inositol trisphosphate
D)Phospholipase A
E)Phospholipase C