Question 1

Methadone is a drug given to treat heroin addicts.It works by binding to the same receptors as heroin but with greater affinity,thereby preventing heroin from binding.This is an example of

Accepted Answer

Methadone competing with heroin for the same receptor sites is an example of competition.

Question 2

Activation of a receptor by a chemical messenger

Accepted Answer

Activation of a receptor involves the binding of a messenger to the ligand-binding site, initiating a response, and often requires a change in receptor conformation.

Question 3

A ligand that is an effective agonist for a chemical messenger

Accepted Answer

A ligand that is an effective agonist for a chemical messenger may have a higher affinity than the messenger for the messenger's receptor and may achieve 50 percent saturation of the messenger's receptor at a lower concentration than that required by the messenger. This allows the ligand to activate the receptor more effectively than the messenger itself. However, the ligand still needs to couple to the binding site of the messenger's receptor to exert its effects. Therefore, choice C is incorrect. Overall, choices A and B are correct, but they are not mutually exclusive, so the correct answer is D.

Question 4

Activation of a receptor that is coupled by G proteins to adenylyl cyclase

Accepted Answer

Activation of a receptor coupled to adenylyl cyclase via G proteins can either increase or decrease cyclic AMP levels, depending on whether the G protein is stimulatory (Gs) or inhibitory (Gi). Changes in cyclic AMP can affect DNA transcription.

Question 5

Which of the following are common means by which binding of an intercellular chemical messenger with a cell's receptor brings about an intracellular response?

Accepted Answer

All the listed mechanisms are common ways by which the binding of a chemical messenger to a receptor can lead to an intracellular response.

Question 6

The significance of plasma membrane receptors for chemical regulators such as hormones and neurotransmitters is that

Accepted Answer

The answer of The significance of plasma membrane receptors for...

Question 7

A 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.The best explanation for this phenomenon is:

Accepted Answer

Cyclic-AMP-dependent protein kinase (PKA) can phosphorylate and activate multiple enzymes, leading to the catabolism of both glycogen and fat.

Question 8

Which of the following statements about G proteins is not correct? G proteins may

Accepted Answer

G proteins do not act as second messengers themselves; they are involved in transmitting signals from activated receptors to other targets, such as enzymes or ion channels, which then produce second messengers.

Question 9

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

Accepted Answer

Down regulation is the process whereby repeated exposure to a hormone can cause a decrease in the number of receptors for that hormone. This is a form of negative feedback where the body reduces the sensitivity to a hormone when it is in excess or has been present for a prolonged duration. This can occur due to various mechanisms such as receptor internalization, degradation, or decreased synthesis.

Question 10

Second messengers

Accepted Answer

Second messengers act in the cell cytoplasm to relay signals from receptors to target molecules within the cell. They are not necessary for all receptor signal transduction mechanisms, do not act as intercellular messengers, do not always activate enzymes, and are not always proteins.

Question 11

Messages,in the form of chemical signals,are sent from one cell to another with only those capable of receiving the specific chemical able to respond to them.Water soluble signals have receptors

Accepted Answer

Water-soluble signals have receptors on the outside of the cell as part of the plasma membrane, and these receptors have a specific structure that is complementary to the chemical message.

Question 12

Oxytocin is a peptide hormone that causes the smooth muscle of the uterus to contract,but it has no effect on the smooth muscle cells of the small intestine.This difference in responsiveness exists because

Accepted Answer

Uterine smooth muscle cells contain specific receptors for oxytocin, which allows the hormone to bind and trigger contraction. On the other hand, the smooth muscle cells of the small intestine do not contain these specific receptors, and therefore oxytocin has no effect on them.

Question 13

Epinephrine activates the cyclic AMP pathway in liver cells.Therefore,epinephrine

Accepted Answer

Epinephrine is a hydrophilic hormone and cannot pass through the cell membrane. Therefore, it is likely to bind to a transmembrane receptor on the surface of liver cells. This binding leads to the activation of a G protein-coupled receptor, which in turn activates the adenylate cyclase enzyme. Adenylate cyclase converts ATP to cyclic AMP (cAMP), which is a second messenger that activates protein kinase A (PKA). PKA phosphorylates target proteins, leading to the physiological response of the cell to epinephrine. Therefore, epinephrine activates the cyclic AMP pathway through second messengers.

Question 14

Receptors for intercellular messengers are most commonly

Accepted Answer

Receptors for intercellular messengers are most commonly integral membrane proteins. These proteins are embedded within the cell membrane and contain binding sites that recognize specific messenger molecules. When a messenger molecule binds to its receptor, it triggers a cellular response. Peripheral membrane proteins and specialized phospholipids within the membrane can also play a role in cellular signaling, but they are not typically the primary receptors for intercellular messengers. Nucleic acids are not involved in cellular signaling in this way.

Question 15

Another term for lipid soluble hormones is

Accepted Answer

Lipid soluble hormones are also known as lipophilic hormones because they are attracted to and soluble in lipids or fats. They easily pass through the cell membrane and bind to intracellular receptors to initiate gene expression. Choice B, C, D, and E are not correct because they refer to different properties of molecules. Lipophobic means "fear of lipids," hydrophobic means "fear of water," hydrophilic means "love of water," and polar means having a separation of electric charge.

Question 16

Cocaine lowers the levels of a chemical messenger in the brain called enkephalin.Researchers have found the number of enkephalin receptors to be higher in cocaine addicts than nonaddicted people.This is an example of

Accepted Answer

Up regulation refers to an increase in the number of receptors for a particular chemical messenger in response to chronic exposure to its ligand. In this case, the chronic exposure to cocaine leads to an up regulation of enkephalin receptors in the brain of addicts. This is a compensatory mechanism that occurs in an attempt to maintain normal brain function despite the inhibitory effect of cocaine on enkephalin release.

Question 17

Cells can control their responsiveness to external chemical regulators by

Accepted Answer

Cells can modulate their sensitivity to external signals by either increasing receptor numbers through exocytosis or decreasing them via endocytosis.

Question 18

Cellular receptors are classified as either intracellular or as plasma membrane bound receptors.Which of the following is not an integrated plasma membrane receptor related description?

Accepted Answer

Regulation of genetic transcription is a function of intracellular receptors, not plasma membrane bound receptors.

Question 19

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

Accepted Answer

There are two types of epinephrine receptors with different affinities for epinephrine that use two different second messenger systems. At low concentrations, epinephrine selectively binds to the beta-2 adrenergic receptor, which leads to the production of cyclic AMP, causing vasodilation. At higher concentrations, epinephrine also binds to the alpha adrenergic receptor, which leads to the production of inositol trisphosphate and intracellular calcium release, causing vasoconstriction. Therefore, the dual effects of epinephrine are due to its differential binding to the two types of receptors with different sensitivities to the hormone.

Question 20

Lipid soluble hormones which pass through the membrane bind with receptors at the nucleus and then increase the rate of mRNA synthesis to

Accepted Answer

Lipid soluble hormones can pass through the cell membrane and bind with receptors in the nucleus, forming a hormone-receptor complex. This complex then binds to specific DNA sequences and increases the rate of transcription of the corresponding genes, leading to an increase in mRNA synthesis. This results in an increase in the production of the protein transcribed from the DNA.

Quiz 5: Control of Cells by Chemical Messengers