cell signaling

What would interfere with the binding of estrogen to the estrogen receptor?

A) A molecule that interferes with second messenger cascades

B) A molecule that prevents estrogen from entering the nucleus

C) The estrogen receptor cleaves estrogen, making it inactive

D) A different molecule that binds to the estrogen receptor on the surface of the cell

B

The alpha subunit of the G-protein is activated by

A) replacing the GTP with GDP.

B) binding to the calcium ions.

C) separating from the gamma and beta subunits.

D) replacing the GDP with GTP.

E) the G-protein becoming phosphorylated.

D

A mutation that alters the G-protein's affinity for GDP, making it less likely to release GDP even when stimulated by a receptor, will have what effect on the cell signaling pathway in which it is involved?

A) The cell will cease to activate the G-protein linked receptor.

B) The pathway will be activated by other receptors, such as receptor tyrosine kinases.

C) The pathway will be over-activated.

D) The pathway will be activated, even in the absence of a signal.

E) The pathway will be under-activated.

NOT A B C

A mutation in the G-protein, decreasing its ability to hydrolyze its bound GTP, will have what effect on the cell signaling pathway in which it is involved?

A) The pathway will be under-activated.

B) The pathway will be activated., even in the absence of a signal.

C) The cell will cease to activate the G-protein linked receptor.

D) The pathway will be activated by other receptors, such as receptor tyrosine kinases.

E) The pathway will be over-activated.

E

TRUE OR FALSE:

The G-protein changes conformation when the GTP replaces the GDP on the alpha subunit.

TRUE

TRUE OR FALSE:

The combination of the calcium and the calmodulin produces the response of the cell to the ligand.

TRUE

The second messenger cAMP is synthesized by the enzyme

A) phosphorylase.

B) ATPase.

C) cAMP phosphodiesterase.

D) adenylyl cyclase.

E) ligase.

D

The binding of epinephrine to its receptor activates a(n)

A) A protein.

B) M protein.

C) D protein.

D) G protein.

E) K protein.

D

The enzyme alpha-kinase adds ________ to proteins.

A) hydroxyls

B) carbonates

C) acetates

D) phosphates

E) benzoates

D

TRUE or FALSE:

Epinephrine has to cross the cell membrane to bind to its receptor in the cytoplasm

FALSE

TRUE or FALSE:

The second messenger cAMP is made from ADP.

FALSE

An example of a second messenger is

A) cAMP.

B) epinephrine.

C) G-protein.

D) ATP.

E) adenylyl cyclase.

A

Arrange the following in the proper order in which they occur during signal amplification.

1. Activation of protein kinase

2. Activation of G protein

3. Activation of adenylyl cyclase

A) 3, 1, 2

B) 2, 1, 3

C) 2, 3, 1

D) 3, 2, 1

E) 1, 2, 3

C

Which of the following statements about signal amplification is TRUE?

A) A single cell surface receptor can activate many G proteins.

B) It takes two cell surface receptors to activate a single G protein.

C) It takes many surface receptors to activate a single G protein.

D) A single cell surface receptor can activate only one G protein.

E) A single cell surface receptor can activate only two G proteins.

A

TRUE or FALSE:

Most signaling molecules are found in low concentrations inside the cytoplasm

TRUE

TRUE or FALSE:

Cell surface receptors may be enzyme-linked or G protein-linked.

TRUE

Which of the following statements is a result of signal amplification?

A) Different types of cells will have differing reactions to a particular signal molecule.

B) Only high concentrations of extracellular signaling molecules can affect a rapid response from a cell.

C) All cell types will react similarly to a particular signal molecule.

D) Small concentrations of extracellular signaling molecules can affect a rapid response from a cell.

E) Endocrine signaling is made possible by signal amplification.

D

Which of the steps in a signal cascade is NOT involved in signal amplification?

A) Inositol triphosphate opens Ca2+ channels in the endoplasmic reticulum

B) A G-protein-linked receptor activates several G-proteins

C) Several extracellular signal molecules bind to several cell surface receptors

D) Adenylyl cyclase enzymes synthesize cAMP, so that the concentration of cAMP significantly rises in the cytoplasm

E) A transcription factor initiates the transcription of many mRNA transcripts

C

When a cell receives a signal, various cellular responses can occur. Classify which type of response each group of proteins could regulate.

ENZYME

A) Associated with breakdown of molecules

B) Altering cell shape

C) Causing cell movement

D) Change in sex characteristics

E) Altering metabolism

F) Activate gene Expression

A E

When a cell receives a signal, various cellular responses can occur. Classify which type of response each group of proteins could regulate.

STRUCTURAL PROTEINS

A) Associated with breakdown of molecules

B) Altering cell shape

C) Causing cell movement

D) Change in sex characteristics

E) Altering metabolism

F) Activate gene Expression

B C

When a cell receives a signal, various cellular responses can occur. Classify which type of response each group of proteins could regulate.

TRANSCRIPTION FACTORS

A) Associated with breakdown of molecules

B) Altering cell shape

C) Causing cell movement

D) Change in sex characteristics

E) Altering metabolism

F) Activate gene Expression

D F

What would interfere with the actions of epinephrine through a G-protein coupled receptor?

A) A molecule that interferes with formation of receptor dimers

B) A molecule that prevents epinephrine from entering the nucleus

C) A different molecule that binds to the G-protein coupled receptor

D) An enzyme in the cell that cleaves epinephrine, making it inactive

C

The advantage of second messengers is best described as

A) Replaces the role of protein phosphatases

B) Prevention of signal inhibition

C) Enhanced specificity of the ligand

D) Amplification of the signal

E) Speeds up ligand-receptor binding

D

Epinephrine inhibits salivary gland activity and muscle cell contraction in the airways, yet stimulates glycogen release in muscle cells and heart muscle cell contraction. How could one hormone have opposing effects on different organs?

A) Cells in tissues that are not responsive contain enzymes that break down epinephrine when it enters the cell.

B) Cells in responsive tissues have signal transduction pathways.

C) Cells in the tissues that are suppressed do not express an epinephrine receptor.

D) Cells in the different tissues would have epinephrine receptors coupled to different signaling pathways.

E) Only responsive tissues are exposed to the epinephrine in the blood stream.

D

In _____, signals pass through a cell junction from one cell to adjacent cells.

direct intracellular signaling

Membrane-bound signals bind to receptors on adjacent cells in the process of _____.

contact-dependent signaling

An example of _____ is when cells release signals that affect themselves and nearby target cells.

autocrine signaling

In _____, cells release signals that affect nearby target cells.

paracrine signaling

Cells release signals that travel long distances to affect target cells during _____.

endocrine signaling

Intracellular receptors are activated by signaling molecules that _____ the plasma membrane.

pass through

In extracellular signaling, ligands bind to _____.

cell surface receptors

Most types of enzyme-linked receptors function as _____

protein kinases

In mammals, receptors for _____ are intracellular

steroid hormones

The second messenger cAMP is synthesized by the enzyme

A) ligase.

B) cAMP phosphodiesterase.

C) adenylyl cyclase.

D) phosphorylase.

E) ATPase.

C

Which of the following statements about inositol triphosphate is FALSE?

A) All of these choices are correct

B) It is synthesized by a membrane-bound enzyme.

C) It binds to and opens Ca2+ channels in the endoplasmic reticulum.

D) It is synthesized by the enzyme phosphatase.

E) It is formed in the cytoplasm.

D

TRUE or FALSE:

Calcium ions serve as second messengers.

TRUE

Which of the following statements is FALSE?

A) Ca2+ and cAMP are both second messengers.

B) Ca2+ and cAMP will have different effects if they are synthesized in different cells.

C) Ca2+ and cAMP are both involved in signal amplification.

D) Ca2+ and cAMP are both protein kinases that will proliferate a phosphorylation cascade.

D

A mutation has occurred, disabling Ca2+ channels in the endoplasmic reticulum so that they can no longer open. The action of which molecule will this mutation this most affect?

A) Phosphodiesterase

B) Calmodulin

C) Adenylyl cyclase

D) PKA

E) Phospholipase C

B

If adenylyl cyclase gets "stuck on," what will be the result to the cell?

A) The cell will die.

B) cAMP will continue to activate kinases.

C) Epinephrine will not be able to dissociate from its receptor.

D) Kinases will not be able to phosphorylate their target proteins.

B

When the acetylcholine receptor sites are not occupied...

A) sodium ions diffuse through and enter the cell.

B) the sodium channels remain closed.

C) sodium ions diffuse through and leave the cell.

D) the sodium channels open.

E) a ligand is formed.

B

When the acetylcholine binds to the receptor sites...

A) sodium ions diffuse through and leave the cell.

B) the sodium channels remain closed.

C) the sodium channels open.

D) a ligand is formed.

E) sodium ions diffuse through and enter the cell.

C

Why is it possible for Na+ to enter the cell when the channel is open?

A) The Na+/K+ pump previously built a high concentration of Na+ on the outside of the cell, so Na+ is diffusing.

B) It is co-transported with a molecule that is moving down its gradient.

C) ATP is used to provide energy to pump Na+.

D) Na+ first moves out of the cell across the lipid bilayer by simple diffusion, and then enters the cell by facilitated diffusion.

E) Na+ are only capable of moving inside the cell.

A

TRUE or FALSE:

The sodium channels in the cell membrane have receptor sites for acetylcholine.

TRUE

The sodium channel is formed by a channel protein. Which of the following statements about channel proteins is TRUE?

A) Channel proteins couple the movement of a molecule to ATP hydrolysis, which provides energy for its active transport.

B) Channel proteins are involved in both active and passive transport.

C) Channel proteins cannot be regulated by the cell.

D) The same molecule that opens a channel protein will also be transported by the channel protein.

E) Channel proteins can be opened or closed by cell signaling molecules.

E

Acetylcholine is a signaling molecule, a neurotransmitter, that is produced in response to many different stimuli. It binds to diverse receptors, and activates different responses in a variety of cells. For instance, it activates contractions in skeletal muscle and inhibits contractions in cardiac muscle. It functions in the central nervous system to make a person aware and awake. Which of the following statements about acetylcholine is FALSE?

A) Acetylcholine triggers many different responses throughout the body so that a coordinated response can be induced due to specific stimuli.

B) Acetylcholine will only bind to and open sodium channels in order to activate a response in a cell.

C) Acetylcholine is capable of eliciting many different responses due to the receptors it binds to and the different effects that are produced within the cytoplasm of the cell.

B

Nicotine is a molecule that is chemically similar to acetylcholine and binds to the same receptors. What affect will nicotine have on the cell shown in the animation?

A) It will open sodium channels.

B) It will close sodium channels.

C) It will excite the cell.

D) It will depress the cell.

E) It will kill the cell.

A

Acetylcholine is a neurotransmitter that conducts a signal from a neuron to a muscle cell, causing it to contract. Atropine is a muscle relaxant that competes with acetylcholine, blocking its activity. Formulate a description of the mechanism by which atropine works.

A) Atropine prevents acetylcholine from binding to a ligand-gated ion channel on the muscle cell.

B) Atropine prevents acetylcholine from leaving the neuron.

C) Atropine prevents acetylcholine from entering the muscle cell.

D) Atropine prevents acetylcholine from binding to a ligand-gated ion channel on the neuron.

A

A mutation in a G-protein prevents the alpha-subunit from dissociating from the beta/gamma-subunit. What effect will this have on the pathway in which the G-protein is involved?

A) The pathway will be over-activated.

B) The pathway will be activated even in the absence of a signal.

C) The pathway will be under-activated.

C

Epinephrine activates glycogen phosphorylase in skeletal muscle cells but not adipose cells. Check all of the possible explanations for this observation.

Check All That Apply

A) Adipose cells may not express epinephrine receptors.

B) Adipose and skeletal muscle may express different epinephrine receptors.

C) Adipose may express a receptor with higher affinity for epinephrine than the skeletal muscle receptor.

D) Adipose may not have a signal transduction pathway coupled to an epinephrine receptor.

E) Adipose may have a receptor and signal transduction pathway but expresses different proteins when exposed to epinephrine.

A B D E

Which of the following cell signaling molecules crosses the cell membrane the easiest?

A) molecules that are small and lipid-insoluble

B) molecules that are small and water-soluble

C) molecules that are small and lipid-soluble

D) molecules that are large and lipid-insoluble

E) molecules that are large and water-soluble

C

Intracellular receptors usually contain binding sites for

A) either DNA or signaling molecules.

B) signaling molecules only.

C) both DNA and signaling molecules.

D) DNA only.

E) neither DNA nor signaling molecules.

C

Intracellular receptors may be found

A) in the nucleus only.

B) in the cytoplasm only.

C) either in the nucleus or on the cell membrane.

D) either in the cytoplasm or on the cell membrane.

E) either in the cytoplasm or the nucleus.

E

The inhibitor of an intracellular signal receptor is defective, such that even when stimulated by a signal molecule, the inhibitor stays bound to the receptor. What effect will this have on the signaling pathway?

A) The signal pathway will be unaffected.

B) The signal molecule will bind to the receptor, but it will not be able to activate it.

C) The signal molecule will bind to and activate the receptor, but the receptor will not be able to bind to the DNA.

D) The signal molecule will not enter the cell.

B

Which of the following molecules might be an intracellular signaling molecule?

A) H2O

B) Na+

C) H+

D) NO

D

TRUE or FALSE:

The response of the target cell to the signal is the same regardless of the type of signal.

FALSE

TRUE or FALSE:

Intracellular receptors bind to specific nucleotide sequences.

TRUE

Lipid soluble hormones...

A) require specific gates to pass through the cell membrane.

B) work as ligands on the surface of the cell membrane.

C) require a membrane receptor protein to enter the cell.

D) diffuse through the cell membrane.

E) enter the cell through active transport.

D

Once inside of the cell, these lipid soluble hormones...

A) bind with a ribosome.

B) bind with a specific receptor molecule inside the cytoplasm.

C) bind with a mRNA molecule.

D) bind with a DNA molecule.

E) bind with a specific receptor molecule inside the nucleus.

B

What is the advantage to the cell of a signaling molecule entering directly into the cell, and binding to and activating a receptor that can induce transcription of DNA?

A) A wide variety of responses can be elicited.

B) The signal cascade can be more tightly regulated than when extracellular signaling molecules are used.

C) The signal can be greatly amplified within the cell.

D) The signaling molecule itself is able to regulate gene expression.

E) A change in gene expression can be quickly accomplished.

E

A cell has a mutation resulting in the aldosterone receptor being unable to efficiently bind to DNA. What effect will this have on the cell?

A) The receptor will become active, but once inside the nucleus it will not be able to initiate transcription, so the signaling pathway will not elicit its response.

B) mRNA will be transcribed, but protein translation will not occur properly, so the signaling pathway will not elicit its response.

C) Aldosterone will not be able to bind to its receptor in the cytoplasm, so the signaling pathway will not elicit its response.

D) Aldosterone cannot be released in the blood as a signaling molecule.

A

Below is an image of the steroid aldosterone and the extracellular signaling molecule, acetylcholine. Why is aldosterone an intercellular signaling molecule while acetylcholine is an extracellular signaling molecule?

A) Aldosterone is hydrophobic and can diffuse across the lipid bilayer, while acetylcholine is charged and cannot pass the lipid bilayer.

B) Aldosterone does not require a receptor to elicit a response, but acetylcholine must bind to a receptor to transduce a signal.

C) Signaling with aldosterone results in gene transcription, while signaling acetylcholine results in an increase in metabolic processes.

D) Aldosterone can bind to DNA, but acetylcholine must bind to receptors.

A

TRUE or FALSE:

The ultimate result of lipid-soluble hormones on cells is the production of proteins.

TRUE

TRUE or FALSE:

The mRNA molecule moves from the cytoplasm to the nucleus and binds to a ribosome where it directs the synthesis of specific proteins.

FALSE

The ligand that activates the G-protein linked receptor is ______.

A) an extracellular signaling molecule

B) Ca2+

C) a G-protein

D) a second messenger

E) GTP

A

When inactive, the alpha subunit of the G-protein is bound to

A) a GTP molecule.

B) a ligand.

C) a GDP molecule.

D) a GTO molecule.

E) an ADP molecule.

C

As a result of the ligand binding to its site on the G-protein-linked receptor,

A) the G-protein changes conformation and GTP replaces the GDP on the alpha subunit.

B) the G-protein changes conformation and the alpha subunit separates from the beta and gamma subunits.

C) the G-protein changes conformation and the alpha subunit rejoins the beta and gamma subunits.

D) the G-protein changes conformation and GDP replaces the GTP on the alpha subunit.

E) the G-protein changes conformation and GTP on the alpha subunit is hydrolyzed, forming GDP.

A

TRUE or FALSE:

The alpha subunit can repeatedly dissociate from and associate with the remainder of the G-protein as long as the ligand is bound to the receptor.

TRUE

TRUE or FALSE:

Inactivation of the alpha subunit occurs when its own phosphorylase activity removes a phosphate from the GTP.

TRUE

Which statement regarding G-protein activation is TRUE?

A) G-proteins are activated by the alpha subunit separating from the beta/gamma subunit.

B) G-proteins are activated by Ca2+.

C) G-proteins are activated by active G-protein-linked receptors.

D) Only the alpha subunit of the G-protein is active.

E) G-proteins are activated when they are bound by an extracellular signaling molecule.

C

If a ligand were stuck in the G-protein-linked receptor, what would be the effect to the cell?

A) The pathway would be deactivated when GDP replaced GTP in the alpha subunit.

B) The cell would stop producing the signal molecule that got stuck.

C) The pathway would be over active.

D) The pathway would be deactivated by the phosphorylase activity of the G-protein's alpha subunit.

E) The pathway would not be activated, even though the signal was present.

C

How can epinephrine have different effects on different cells?

A) cAMP activates different kinases in different cells.

B) Different cells have different receptors that bind epinepherine.

C) All of these are TRUE.

D) Different cells activate different enzymes as a result of epinepherine binding.

C

Acetylcholine acts at a G-protein linked receptor on heart muscle cells to make the heart beat more slowly. When the G-protein is activated, the βγ-subunit binds to a K+ ion channel, causing it to open. Which one of the following would enhance the effect of acetylcholine?

A) Mutations in the G-protein that weaken its affinity for GTP.

B) Mutations in the receptor that weaken the interaction between the receptor and the G-protein.

C) Mutations in the receptor that weaken the interaction between the receptor and acetylcholine.

D) A mutation in the G-protein preventing the α-subunit from separating from the βγ-subunit.

E) Mutations in the G-protein that inhibit its phosphatase activity.

E

Which of the following characteristics is NOT a reason that cAMP is considered a second messenger?

A) It can quickly diffuse through the cell.

B) It is produced in response to a cellular signal binding a receptor.

C) It is made from ATP.

D) All of these make cAMP a second messenger.

C

Epinephrine binds to

A) Alpha-adrenergic receptors on the cell membrane of liver cells.

B) Beta-adrenergic receptors in the cytoplasm of liver cells.

C) Beta-adrenergic receptors in the nucleus of liver cells.

D) Alpha-adrenergic receptors in the cytoplasm of liver cells.

E) Beta-adrenergic receptors on the cell membrane of liver cells.

E

The binding of epinephrine to its receptor activates ________ which in turn activates ________.

A) protein kinase A ; G protein

B) G-protein ; protein kinase A

C) protein kinase A ; adenylyl cyclase

D) G-protein ; adenylyl cyclase

E) adenylyl cyclase ; G-protein

D

The enzyme phosphorylase catalyzes the conversion of

A) glucose into glucose-6-phosphate.

B) glucose into glycogen.

C) glycogen into glucose.

D) glucose-6-phosphate into glycogen.

E) glycogen into glucose-6-phosphate.

A

Epinephrine is produce by the central nervous system and has an effect throughout the body, such as in the heart, liver, and blood vessels. Epinephrine is part of what kind of signaling?

A) Paracrine signaling

B) Endocrine signaling

C) Autocrine signaling

D) Contact-dependent signaling

E) Direct intercellular signaling

B

Which of the following statements about cAMP is FALSE?

A) It activates the same signal cascade in many different cell types.

B) It is synthesized from ATP.

C) It is produced by the action of adenylyl cyclase in many different cell types.

D) It acts as a second messenger in many different cell types.

A

Epinephrine causes muscles to contract and the heart and lungs to increase respiration and blood flow. In combination with epinephrine causing glucose production and secretion from the liver, how does epinephrine elicit a system wide response?

A) Muscle contractions require copious amounts of ATP, which is produced by the oxidation of glucose. Oxygen is provided by the increase of respiration and blood flow.

B) Glucose provides energy for muscle contractions, which are stimulate by high concentrations of oxygen. Oxygen is provided by the increase in respiration and blood flow.

C) Oxygen stimulates muscle contraction, and is supplied to the muscles by the increase in respiration and blood flow. ATP provides the energy for muscle contractions, and is formed in the liver when glucose is converted to glycogen.

D) Glucose provides energy for muscle contractions, resulting in high levels of pyruvic acid. The pyruvic acid is flushed from the muscle cells by the increase in respiration and blood flow.

A

TRUE or FALSE:

Epinephrine causes the liver to uptake glucose from the bloodstream during the fight-or-flight response.

FALSE

TRUE or FALSE:

The conversion of ATP into cAMP is catalyzed by the enzyme adenylyl cyclase.

TRUE