BIO 381 - Chapter 15

Where are steroid receptors generally located and where do they bind the steroid hormone once it enters the cell? a) They are located and bind the steroids in the cytoplasm. b) They are located and bind the steroids in the middle of the cell membrane. c) They are located and bind the steroids on the extracellular membrane surface. d) The receptors are located in the cytoplasm but they bind their ligands in the lysosomes.

a) They are located and bind the steroids in the cytoplasm.

The IP3 receptor is also a __________. a) a calcium channel b) a calcium pump c) a sodium channel d) a potassium channel

a) a calcium channel

Ras possesses all the characteristics EXCEPT being: a) a cytosolic protein. b) inactivated by hydrolysis of bound GTP. c) activated by GEFs. d) involved in cell division and differentiation. e) a monomeric G protein.

a) a cytosolic protein.

G-proteins are heterotrimers composed of alpha, beta and gamma subunits. When GDP is bound to the alpha subunit of the complex, the protein is inactive. When the GTP is replaced with a GTP at the alpha subunit, via interaction with a G-protein-coupled receptor-ligand complex, the G-protein complex is activated. a) alpha subunit b) beta subunit c) gamma subunit d) delta subunit

a) alpha subunit

Which of the following characteristics is NOT true of diabetes type 2? a) decreased production of insulin b) resistance in insulin receptors c) related to a high-calorie diet and a sedentary lifestyle d) elevated levels of blood glucose e) cardiovascular damage

a) decreased production of insulin

The activation of RTKs is characterized by: a) dimerization and autophosphorylation. b) a kinase cascade. c) hydrolysis of GTP. d) opening of a ligand-gated channel. e) a subsequent increase in epidermal growth factor.

a) dimerization and autophosphorylation.

The _________ pathway of apoptosis is one in which external stimuli activate apoptosis via a signaling pathway. a) extrinsic b) external c) intrinsic d) peripheral e) integral

a) extrinsic

The level of blood glucose is lowered by _______ and is increased by _________. a) insulin; glucagon b) TUG; GLUT4 c) GLUT4; glycogen synthase d) glucagon; insulin e) glycogen synthase; insulin

a) insulin; glucagon

Where is the receptor for IP3 located? a) on the surface of the SER b) on the interior of the SER c) on the plasma membrane d) on the interior of the RER and the Golgi complex

a) on the surface of the SER

Which of these steps is present in the intrinsic pathway of apoptosis, but is not present in the extrinsic pathway of apoptosis? a) release of cytochrome c from the mitochondria b) activation of executioner caspases c) binding of TNF to a trimeric receptor d) procaspases appear in the cytoplasm e) phosphatidylserine is displayed on the outside of the plasma membrane

a) release of cytochrome c from the mitochondria

In autocrine signaling, _________. a) the cell producing the messenger expresses receptors on its surface that can respond to that messenger b) the messenger molecules travel only short distances through the extracellular space to cells that are in close proximity to the cell that is generating the message c) the messenger molecules reach their target cells via passage through bloodstream d) the messenger molecules are usually limited in their ability to travel around the body because they are inherently unstable or they are degraded by enzymes or they bind to extracellular matrix

a) the cell producing the messenger expresses receptors on its surface that can respond to that messenger

Signal transduction is: a) the process by which information from outside the cell is translated into changes that occur inside a cell. b) the binding of a signal molecule to a receptor. c) activation of a G protein. d) amplification of a signal through a series of phosphorylations. e) generation of a large response from a small number of molecules.

a) the process by which information from outside the cell is translated

Which of the following has NOT been identified as a second messenger? a) Ca2+ b) ATP c) diacylglycerol d) IP3 e) nitric oxide

b) ATP

What is the relationship between the formation of IP3 and the elevation of intracellular [Ca2+]? a) Binding of IP3 to the membrane causes releases of calcium. b) Binding of IP3 to the smooth ER causes releases of calcium. c) Binding of IP3 to its receptor in bone tissues triggers release of calcium. d) None of these is the correct answer.

b) Binding of IP3 to the smooth ER causes releases of calcium.

Once the kinase domain of receptor protein-tyrosine kinase has been activated, what does the activated receptor protein-tyrosine kinase do? a) The receptor subunits denature. b) Each receptor subunit phosphorylates its partner on tyrosine residues found in regions adjacent to the kinase domain. c) Each receptor subunit phosphorylates itself on tyrosine residues found in regions adjacent to the kinase domain. d) The receptor subunits dephosphorylate each other. e) The receptor subunits refold into a more effective conformation.

b) Each receptor subunit phosphorylates its partner on tyrosine residues found in regions adjacent to the kinase domain.

Arrestins form a small group of proteins that bind _______ and compete for binding to _______ with ____________. a) GPCRs, gene promoters, heterotrimeric G proteins b) GPCRs, those GPCRs, heterotrimeric G proteins c) gene promoters, gene promoters, heterotrimeric G proteins d) GPCRs, those GPCRs, heterodimeric G proteins

b) GPCRs, those GPCRs, heterotrimeric G proteins

How is Ras activity turned off? a) It is turned off by phosphorylation. b) It is turned off by hydrolysis of its bound GTP to GDP. c) It is turned off by hydrolysis of its bound GDP to GTP. d) It is turned off by an allosteric inhibitor. e) It is turned off by hydrolysis of its bound GTP to GMP.

b) It is turned off by hydrolysis of its bound GTP to GDP.

How do docking proteins lend versatility to the signaling process mediated by the receptor protein-tyrosine kinase? a) The same docking protein will have different binding affinities in different cells. b) The ability of the receptor to turn on signaling molecules can vary with the docking proteins expressed in a particular cell. c) Docking proteins behave differently in different cells. d) All of the docking proteins are continually present but they work at different times in a cell life cycle.

b) The ability of the receptor to turn on signaling molecules can vary with the docking proteins expressed in a particular cell.

Which of the following features would be a requirement for a receptor that exhibits ligand-mediated dimerization? a) The ligand has only one binding site for receptors. b) The ligand has two binding sites for receptors. c) The receptor must have a phenylalanine residue in a specific location. d) The receptor must have a molecular weight of 50,000 daltons. e) Ligand binding causes a conformational shift that reveals a binding site for another receptor.

b) The ligand has two binding sites for receptors.

Which of the following can lead to the formation of phosphotyrosine docking sites for the SH2 protein domain? a) integrins. b) GPCRs. c) RTKs. d) All of the choices are correct. e) both GPCRs and RTKs, but not integrins.

d) All of the choices are correct.

What allows cells to respond to an extracellular messenger molecule? a) They must have ion channels. b) They must have a lipid bilayer that allows a response. c) They must have receptor proteins exposed on the inner plasma membrane surface. d) They must express receptors that specifically recognize and bind that particular messenger molecule.

d) They must express receptors that specifically recognize and bind that particular messenger molecule.

What phrase below is an accurate description of caspases? a) cysteine proteases b) activated at an early stage of apoptosis c) proteases with a key cysteine residue in their catalytic site d) all of these answers are correct

d) all of these answers are correct

What holds Ras at the inner surface of the plasma membrane? a) weak interactions with the phospholipid head groups b) weak interactions with integral membrane proteins c) hydrophilic interactions of the Ras protein with the interior of the phospholipid bilayer d) attachment to a lipid group that is embedded in the inner leaflet of the bilayer e) attachment to a carbohydrate group that is embedded in the inner leaflet of the bilayer

d) attachment to a lipid group that is embedded in the inner leaflet of the bilayer

Which molecule is the second messenger in a pathway initiated by binding of epinephrine to a cell membrane? a) epinephrine b) G protein c) adenylyl cyclase d) cAMP e) GTP

d) cAMP

Once activated, what does caspase-9 itself activate? a) phospholipase C b) protein kinase A c) other initiator caspases d) downstream executioner caspases e) downstream caspase-8

d) downstream executioner caspases

Phosphorylation of a protein can change its behavior in all of these ways EXCEPT: a) it can increase or decrease protein-protein interactions. b) it can move from one cell compartment to another. c) it can initiate protein degradation. d) it can initiate protein synthesis. e) it can activate or inactivate an enzyme.

d) it can initiate protein synthesis.

MAPK: a) is the final protein kinase in the Ras signaling cascade. b) can cause cell proliferation. c) is phosphorylated by an MAPKK. d) performs different functions in different groups of organisms. e) all of the choices are correct.

e) all of the choices are correct.

Which cells secrete epinephrine? a) α-cells in the pancreas b) β- Medulla -cells in the pancreas c) γ- Medullary -cells in the pancreas d) cortical cells in the adrenal gland e) medulla cells in the adrenal gland

e) medulla cells in the adrenal gland

What behavior allows G proteins to inactivate themselves? a) GTPase activity of the α subunit b) activation of the effector c) binding to the receptor d) dissociation of the subunits e) inhibition of arrestins

a) GTPase activity of the α subunit

Imagine that you are conducting experiments and you have a cell line that responds to an external hormonal signal by entering the apoptotic pathway. How would these cells respond to this hormonal signal if you could instantly and completely inactivate the Bcl-2 protein? a) Since Bcl-2 normally protects cells from apoptosis, loss of this protein would cause these cells to go through apoptosis. b) Since Bcl-2 normally protects cells from apoptosis, loss of this protein would prevent apoptosis. c) Since Bcl-2 normally promotes apoptosis, loss of this protein would prevent apoptosis. d) None of these is the correct answer.

a) Since Bcl-2 normally protects cells from apoptosis, loss of this protein would cause these cells to go through apoptosis.

Epinephrine binds to the same type of receptors in liver and smooth muscle cells. Yet liver cells break down glycogen and smooth muscle cells relax. How can the same hormone produce such different responses? a) The same receptors activate different second messengers. b) The same hormone and its second messengers activate different intracellular proteins with different functions. c) The same enzyme that breaks down glycogen also relaxes muscle. d) Epinephrine activates the receptor in one cell and inhibits it in the other. e) Glycogen is molecularly bound to actin.

b) The same hormone and its second messengers activate different intracellular proteins with different functions.

Desensitization __________. a) allows a cell to change its environment, rather than continuing to fire endlessly in the presence of an unchanging environment b) allows a cell to respond to a change in its environment, rather than continuing to fire endlessly in the presence of an unchanging environment c) allows a cell to die d) allows a cell to alter its conformation

b) allows a cell to respond to a change in its environment, rather than continuing to fire endlessly in the presence of an unchanging environment

What is the name of a calcium-binding protein that acts in conjunction with calcium to bring about the responses associated with cytoplasmic rises in calcium ion concentration? a) calpectin b) calmodulin c) calcariain d) callistin e) modulocalcin

b) calmodulin

The activation of a common effector by signals from a variety of unrelated receptors, each of which binds to its own ligand, is called _________. a) divergence b) convergence c) crosstalk d) transvergence e) coherence

b) convergence

Sometimes an enzyme is activated by a receptor and brings about the cellular response by generating a second messenger. Such an enzyme is called a(n) __________. a) activator b) effector c) affector d) refractor e) generator

b) effector

Cholera toxin exerts its effect on epithelial cells in the intestinal lumen by: a) blocking the G protein-coupled receptor. b) inhibiting GTPase activity in the Gα subunit. c) accelerating the hydrolysis of GTP. d) preventing production of cAMP. e) destruction of adenylyl cyclase.

b) inhibiting GTPase activity in the Gα subunit.

The effect of inositol triphosphate is usually transient because __________. a) it is so stable b) it is rapidly inactivated enzymatically c) it is slowly activated enzymatically d) it is so big e) it is so small

b) it is rapidly inactivated enzymatically

After an RTK is internalized by clathrin-mediated endocytosis, it maysuffer all of the following fates EXCEPT: a) being incorporated into endosomal signaling complexes. b) traveling in a retrograde manner through the Golgi complex. c) being degraded in lysosomes. d) engaging in intracellular signaling. e) being returned to the plasma membrane.

b) traveling in a retrograde manner through the Golgi complex.

Why are G-protein coupled receptors often known as 7TM receptors? a) They have 7 tyrosine-methionine dipeptides in their structure. b) They have 7 transmembrane β-pleated sheets. c) They have 7 transmembrane α-helices. d) They have 7 methionine-tryptophan dipeptides in their structure.

c) They have 7 transmembrane α-helices.

Ryanodine and IP3 receptors are found on ________ membranes and ________ membranes, respectively. a) plasma, vesicular b) plasma, plasma c) endoplasmic reticulum, endoplasmic reticulum d) outer, inner e) endoplasmic reticulum, plasma

c) endoplasmic reticulum, endoplasmic reticulum

Which of the following events is NOT characteristic of apoptosis? a) phagocytosis b) decreased volume c) inflammation d) loss of adhesion to neighboring cells e) fragmentation of chromatin

c) inflammation

The _________ pathway of apoptosis is one in which internal stimuli activate apoptosis. a) extrinsic b) external c) intrinsic d) peripheral e) integral

c) intrinsic

What role do activated steroid receptors play in the cell? a) activation of inactive enzymes b) inactivation of active enzymes c) ligand-regulated transcription factors d) opening of specific ion channels e) activation of cytoplasmic proteins

c) ligand-regulated transcription factors

Following a nerve impulse, what triggers the opening of plasma membrane voltage-gated Ca2+ channels? a) membrane hyperpolarization b) binding of an appropriate ligand c) membrane depolarization d) membrane hypopolarization e) binding of K+ ions

c) membrane depolarization

What enzyme below does diacylglycerol (DAG) recruit and activate? a) phosphatidylinositol (PI)-specific phospholipase C-β b) protein kinase A c) protein kinase C d) glycogen phosphorylase e) phosphorylase kinase

c) protein kinase C

Which amino acids are known to be phosphorylated by most protein kinases? a) tyrosine, threonine, glycine b) threonine, serine, tryptophan c) serine, threonine, tyrosine d) phenylalanine, serine, tyrosine e) serine, leucine, tyrosine

c) serine, threonine, tyrosine

In endocrine signaling, _________. a) the cell producing the messenger expresses receptors on its surface that can respond to that messenger b) the messenger molecules travel only short distances through the extracellular space to cells that are in close proximity to the cell that is generating the message c) the messenger molecules reach their target cells via passage through bloodstream d) the messenger molecules are usually limited in their ability to travel around the body because they are inherently unstable or they are degraded by enzymes or they bind to extracellular matrix

c) the messenger molecules reach their target cells via passage through bloodstream

Trans-autophosphorylation refers to ___________________. a) the ability of G protein coupled receptors to phosphorylate each other b) the ability of phosphate groups to be removed from receptor-protein tyrosine kinases c) the protein kinase activity of one receptor-protein tyrosine kinase subunit of a dimer phosphorylating the tyrosine residues in the cytoplasmic domain of the other receptor of the dimer d) the protein kinase activity of one receptor-protein tyrosine kinase subunit of a dimer phosphorylating the tyrosine residues in the extracellular domain of the other receptor of the dimer

c) the protein kinase activity of one receptor-protein tyrosine kinase subunit of a dimer phosphorylating the tyrosine residues in the cytoplasmic domain of the other receptor of the dimer

Which of these is an example of signal divergence? a) Two different signals both stimulate the same response. b) A single event can participate in more than one pathway consecutively. c) The same response is stimulated by two different hormones. d) A single hormone can send out a signal along a variety of different pathways. e) Two different signals can initiate two different responses.

d) A single hormone can send out a signal along a variety of different pathways.