Cell Bio, Exam 4 (quiz questions/answers)

Ligand-activated G protein-coupled receptor signaling involves all of the following EXCEPT: hormone. the receptor. GTPase. effector protein. Actually, all of these are involved.

Actually, all of these are involved.

Extracellular signaling includes all of the following EXCEPT: signaling by membrane-attached proteins. autocrine signaling. paracrine signaling. endocrine signaling. Actually, these are all forms of extracellular signaling.

Actually, these are all forms of extracellular signaling.

Which statement accurately describes how to experimentally determine Kd? Add ligand to a solution containing the receptor and measure how much ligand is required to saturate the receptor. Add two ligands to a solution containing the receptor and examine receptor inactivation. Add two ligands to a solution containing the receptor, one with high affinity and one with low affinity. Determine how well the two ligands bind to each other. Add ligand to a solution and determine the concentration of ligand necessary for half of the receptors to be bound. Add ligand to a solution containing the receptor and determine what percentage loses the ligand.

Add ligand to a solution and determine the concentration of ligand necessary for half of the receptors to be bound.

Different G proteins, while associating with different receptors, can: use the same second messenger. lead to activation of the same effector. mediate responses to the same extracellular ligand. All of the answers are correct.

All of the answers are correct.

Glycogenolysis, the breakdown of glycogen to glucose, is stimulated by: Please choose the correct answer from the following choices, and then select the submit answer button. epinephrine in muscle cells. acetylcholine in muscle cells. production of cyclic AMP (cAMP) in liver cells. All of the answers are correct. None of the answers is correct

All of the answers are correct.

Signaling pathways that are triggered by protein cleavage include: Please choose the correct answer from the following choices, and then select the submit answer button. Notch/Delta. SREBP. Those involved in Alzheimer's disease. All of the answers are correct. None of the answers is correct.

All of the answers are correct.

Rhodopsin is different from most G protein receptors in that: there are over 10 million copies of the protein in a rod cell. it is organized into stacks of membranes. it does not respond to a ligand. All of the answers are correct. None of the answers is correct.

All of the answers are correct. Rod cells sense light with the aid of a light-sensitive GPCR known as rhodopsin. Rhodopsin consists of the protein opsin, which has the usual seven-transmembrane segment GPCR structure, covalently linked to a light-absorbing pigment called retinal. Rhodopsin, found only in rod cells, is localized to the thousand or so flattened membrane disks that make up the outer segment of each of these rod-shaped cells Rhodopsin (R) differs from other GPCRs in that binding of a ligand is not what activates the receptor. Rather, absorption of a photon of light by the bound retinal is the activating signal.

Which statement is NOT true regarding GPCRs? They are exclusively membrane proteins. They have a protein capable of GTP hydrolysis. Ligand binding correlates with GTPase activity. They have a cytoplasmic domain. All of the statements are true regarding GPCRs.

All of the statements are true regarding GPCRs. G protein-coupled receptors have four extracellular segments.

Which of the following statements about cadherins is true? They are glycoproteins. They are calcium-dependent. They join cells of a similar type to one another. All of these answers are correct.

All of these answers are correct

Which of the following statements about focal adhesions is true? They anchor cells to the substratum. They can be rapidly disassembled upon a changing environment. They may act as a type of sensory structure leading to cell growth. All of these answers are correct.

All of these answers are correct.

Which of the following statements about gap junctions is true? They are found in animal cell only. They are composed of the protein connexin. They are specialized for intercellular communication. All of these are correct answers.

All of these are correct answers

XXX Which of the following general statement(s) about a G protein-coupled receptor is (are) TRUE? a. It contains 12 transmembrane domains. X b. It is positioned with the N-terminus on the cytoplasmic face of the membrane. c. It is positioned with the C-terminus on the cytoplasmic face of the membrane. d. All of the above

C.

In T-cells in the immune system, activation of transcription factors by calmodulin involves: Ca++-calmodulin binding the transcription factor and activating it allosterically. Ca++-calmodulin activating a phosphatase that removes an inhibitory phosphate. calmodulin unbound to Ca++ inhibiting a kinase that phosphorylates and inhibits transcription factors. All of the answers are correct. None of the answers is correct.

Ca++-calmodulin activating a phosphatase that removes an inhibitory phosphate.

Common cellular "second messengers" include: phosphatidylinositol. Ca++. GTP. both phosphatidylinositol and Ca++. both Ca++ and GTP.

Ca++.

Which statement is NOT true regarding second messengers? Extracellular ions are examples of second messengers. They perpetuate a signaling cascade to produce an effect in the cell. Small proteins are examples of second messengers. They interact with effector proteins. All of the statements are true regarding second messengers.

Extracellular ions are examples of second messengers second messenger: A small intracellular molecule (e.g., cAMP, cGMP, Ca2+, DAG, and IP3) whose concentration increases (or decreases) in response to binding of an extracellular signal and that functions in signal transduction

How would an inhibitor of cGMP phosphodiesterase affect nitric oxide signaling? It would cause blood vessel dilation by maintaining high PKG activity. It would increase cGMP levels by increasing PLC levels. It would block NO signaling by inhibiting NO synthase. It would increase NO signaling by increasing cytosolic Ca2+ levels. None of the answers is correct.

It would cause blood vessel dilation by maintaining high PKG activity. nitric oxide (NO), which causes relaxation of the smooth muscle cells surrounding the blood vessels

Which statement is NOT true regarding the mechanism of protein kinase regulation? The action of kinases is counteracted by proteins known as phosphatases. Kinases add phosphate groups to specific amino acids on target proteins, such as tyrosine. Kinase activity results in the formation of an ATP molecule. Phosphorylation of different sites on the target protein can produce different effects. All of the statements are true.

Kinase activity results in the formation of an ATP molecule.

In the MAP kinase cascade: Ras follows MEK. MEK precedes MAPK. Ras follows Raf. All of the answers are correct. None of the answers is correct.

MEK precedes MAPK.

How does ubiquitin-dependent regulation of receptor proteins differ in monoubiquitination versus polyubiquitination? Please choose the correct answer from the following choices, and then select the submit answer button. Monoubiquitination requires a ubiquitin ligase protein but polyubiquitination does not. Monoubiquitination results in lysosomal degradation versus proteasomal degradation with polyubiquitination. Monoubiquitination promotes receptor activation, whereas polyubiquitination results in receptor degradation. Both the first and second answers are correct. All of the answers are correct.

Monoubiquitination results in lysosomal degradation versus proteasomal degradation with polyubiquitination.

Which statement is TRUE regarding cAMP? cAMP is an example of a nucleotide found in RNA. cAMP and Ca2+ ions are interchangeable in signaling pathways. cAMP is an example of a ligand. cAMP binds to and activates G proteins. None of the statements is true regarding cAMP.

None of the statements is true regarding cAMP. cyclic AMP (cAMP): A second messenger, produced in response to hormonal stimulation of certain G protein-coupled receptors, that activates protein kinase A

Wnt-1 is a proto-oncogene. Which statement MOST accurately describes what this means? In the absence of Wnt-1, cell growth is inhibited. In the absence of Wnt-1, cells become cancerous. Normal Wnt-1 expression often prevents cell growth. Overexpression of Wnt-1 causes cells to become cancerous. Overexpression of Wnt-1 causes inhibition of growth.

Overexpression of Wnt-1 causes cells to become cancerous.

A cell is lacking the CBP/P300 protein (CREB co-activator). How will GPCR signaling be altered in this cell? Signaling will be unaffected because CREB activation still occurs. Signaling will be unaffected because PKA activation still occurs. Signaling will be inhibited because CREB will no longer localize to the nucleus. Signaling will be inhibited because CREB is necessary for RNA polymerase activity. Correct: Signaling will be inhibited because activated CREB will no longer be able to activate transcription of the target gene. Signaling will be inhibited because activated CREB will no longer be able to activate transcription of the target gene.

Signaling will be inhibited because activated CREB will no longer be able to activate transcription of the target gene.

Before activation, transforming growth factor β (TGF-β) proteins are stored: as the inactive form in the nucleus. as the inactive form in the cytoplasm. as the inactive form in the extracellular matrix. as the active form in the cytoplasm. None of the answers is correct.

TGF-β Proteins Are Stored in an Inactive Form in the Extracellular Matrix

A SOCS protein lacks the SOCS box. How does this affect its ability to regulate receptor signaling? The SOCS protein will not be able to bind to the receptor. The SOCS protein will not be able to promote lysosomal-dependent degradation. The SOCS protein will not be able to block binding of other SH2 domain-containing proteins. The SOCS protein will not be able to recruit a ubiquitin ligase. All of the answers are correct.

The SOCS protein will not be able to recruit a ubiquitin ligase.

A G protein has a Gα subunit that is incapable of GDP release. How will this impact the GPCR? The α subunit will be incapable of binding to the Gβ and Gγ subunits. The GPCR will be unable to bind ligand. The α subunit will not dissociate from the GPCR. The Gβ and Gγ subunits will not interact. None of the answers is correct.

The α subunit will not dissociate from the GPCR.

Which characteristic is NOT true of cytokine receptors? They consist of two domains with β strands The contain an extracellular ligand-binding domain They contain an intracellular kinase domain They dimerize with another receptor when active Actually, all of these characteristics are true of cytokine receptors.

They contain an intracellular kinase domain The extracellular domains of these cytokine receptors are constructed of two subdomains, each of which contains seven conserved β strands folded together in a characteristic fashion.

How are the Wnt- and Hedgehog-receptor proteins different from GPCRs? Wnt/Hedgehog receptors are not multi-spanning membrane proteins. Wnt/Hedgehog receptors do not have an extracellular ligand-binding domain. Wnt/Hedgehog receptors do not associate with GTPases. Wnt/Hedgehog receptors do not associate with intracellular soluble proteins. All of the answers are correct.

Wnt/Hedgehog receptors do not associate with GTPases.

XXX What is an effector? a. A molecule that brings about a cellular response to a signal. X b. A molecule that brings a signal to a cellular response. c. A molecule that brings enzymatic changes to a cell. d. None of these is the correct answer.

X

XXX What is the effect of GAPs on the G protein-mediated response? a. GAPs dramatically shorten the duration of the response. b. GAPs have no effect on the response. X c. GAPs speed up the response. d. GAPs dramatically lengthen the duration of the response.

X

XXX Which molecules below inhibit the release of a bound GDP from a monomeric G protein, thus maintaining the protein in the inactive, GDP-bound state? a. GDIs b. GAPs c. Arrestins X d. GEFs

X

A FRET system is established (Figure 15-18) in which the Gβα subunits are tagged with YFP and the Gα subunit is tagged with CFP. If the three subunits are together when the CFP is activated, the YFP will absorb the blue light and emit yellow. If the Gα subunit is unable to associate with the GPCR, would you expect to see yellow light? No, without interaction with the GPCR, the Gα subunit will not bind to GTP, which is necessary for the three subunits to interact. Yes, if not bound to the GPCR, the three subunits will remain inactive and together. Yes, without GPCR binding, the Gα subunit cannot hydrolyze GTP and thus the subunits remain intact. No, association with the GPCR is necessary for the interaction among the three subunits. No, without interaction with the GPCR, the Gα subunit will not bind to GDP, which is necessary for the three subunits to interact.

Yes, if not bound to the GPCR, the three subunits will remain inactive and together.

Protein kinase A recognizes particular target sequences characterized by: a tyrosine, preceded by acidic amino acids and followed by a hydrophobic residue. a serine or threonine, preceded by acidic amino acids and followed by a hydrophobic residue. a tyrosine, preceded by basic amino acids and followed by a hydrophobic residue. a serine or threonine, preceded by basic amino acids and followed by a hydrophobic residue. None of the answers is correct.

a serine or threonine, preceded by basic amino acids and followed by a hydrophobic residue.

What event is responsible for terminating signal transduction by RTKs? a. receptor internalization b. dephosphorylation of the receptor c. degradation of the ligand d. phosphorylation of the receptor

a. receptor internalization

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

a. GPCRs, those GPCRs, heterotrimeric G proteins

How is signaling by an activated Ga subunit terminated? a. The bound GTP is hydrolyzed to GDP. b. The bound GDP is hydrolyzed to GTP. c. The Ga subunit releases GDP and binds GTP. d. The bound GDP is phosphorylated to GTP.

a. The bound GTP is hydrolyzed to GDP.

Which of the following is not a common intracellular second messenger? a. adenosine triphosphate (ATP) b. 1,2 diacylglycerol (DAG) c. inositol 1,4,5-trisphosphate (IP3) d. 3'-5' cyclic guanine monophosphate (cGMP)

a. adenosine triphosphate (ATP)

Smooth muscle contraction is triggered by _____ and relaxation is triggered by _____. acetylcholine; nitric oxide (NO) acetylcholine; cyclic AMP (cAMP) nitric oxide (NO); acetylcholine cyclic AMP (cAMP); acetylcholine None of the answers is correc

acetylcholine; nitric oxide (NO)

To trigger relaxation of smooth muscle, all of the following are required EXCEPT: acetylcholine to signal an endothelial cell. an endothelial cell to produce acetylcholine. an endothelial cell to produce nitric oxide (NO). cyclic GMP (cGMP) to cause a reduction of intracellular Ca++ in the smooth muscle cell. Actually, all of these are required.

an endothelial cell to produce acetylcholine. Nitric oxide is synthesized in endothelial cells in response to activation of acetylcholine GPCRs, phospholipase C, and the subsequent elevation in cytosolic Ca2+. NO diffuses locally through tissues and activates an intracellular NO receptor with guanylyl cyclase activity in nearby smooth muscle cells. The resulting rise in cGMP activates protein kinase G, leading to relaxation of the muscle and thus vasodilation

xxx The activation of a variety of different effectors by signals from a single receptor binding a single ligand is referred to as _______________. a. crosstalk b. convergence c. divergence d. transvergence

b

What is meant by "signal transduction'? a. Overall process of sending chemical messages. b. Overall process of translating information from an extracellular messenger into cellular changes. c. Overall process of translating information from an intracellular messenger into extracellular changes. d. None of these is the correct answer.

b. Overall process of translating information from an extracellular messenger into cellular changes.

A(n) ____________ is an extracellular messenger molecule that usually binds to a receptor at the extracellular surface of the responding cells. a. secondary messenger b. ligand c. ligature d. binders

b. ligand

Adrenergic receptors

bind ligand via their extracellular loops.

Calmodulin: has two binding sites for Ca++. binds cooperatively to Ca++ ions. undergoes a conformational shift upon binding two Ca++ ions. is not particularly sensitive to changes in Ca++ concentrations. None of the answers is correct.

binds cooperatively to Ca++ ions.

Protein kinase A is activated when cyclic AMP: binds to the catalytic subunit. binds to the regulatory subunit. triggers Ca++ entrance to the cytosol. All of the answers are correct. None of the answers is correct; protein kinase A is not activated by cAMP.

binds to the regulatory subunit. protein kinase A (PKA): Cytosolic enzyme that is activated by cyclic AMP (cAMP) and functions to phosphorylate and thus regulate the activity of numerous cellular proteins; also called cAMP-dependent protein kinase

Termination of light detection requires: activation of guanylate cyclase. hydrolysis of bound GTP to GDP. activation of an esterase. both activation of guanylate cyclase and hydrolysis of bound GTP to GDP. both hydrolysis of bound GTP to GDP and activation of an esterase.

both activation of guanylate cyclase and hydrolysis of bound GTP to GDP.

A single ligand can have variable effects by binding: the same receptor but triggering different responses in different cell types. different receptors in different cell types. different receptors and triggering different responses in the same cell type. both different receptors in different cell types and the same receptor but triggering different responses in different cell types. both different receptors in different cell types and different receptors and triggering different responses in the same cell type.

both different receptors in different cell types and the same receptor but triggering different responses in different cell types.

Which of the following are enzyme pairs that catalyze opposite reactions? a. MEK and MAP kinase b. NF-kB and I-kB c. PI-3 kinase and PTEN phosphatase d. JAKs and STATs e. none of the above

c. PI-3 kinase and PTEN phosphatase

Binding of hormone to a receptor tyrosine kinase causes all of the following, except: a. autophosphorylation of the receptor b. dimerization of the receptor c. hydrolysis of GTP bound to RAS d. activation of Ras through an interaction with GRB2 and SOS

c. hydrolysis of GTP bound to RAS

What ion is required to maintain the proper integrin structure and to facilitate ligand binding? calcium magnesium sodium manganese

calcium

Light signals of fewer than 10 photons can be detected by vertebrate eyes due to amplification by all of the following EXCEPT: activation of multiple G protein subunits by a single rhodopsin. activation of multiple esterases by G protein subunits. large-scale production of cGMP by esterases. closing of tens of thousands of cation channels by cGMP. Actually, all of these play parts in the signal amplification.

closing of tens of thousands of cation channels by cGMP

Some bacterial toxins can interfere with G proteins, leading to all of the following EXCEPT: constriction of arteries through the epinephrine receptor. loss of ions, and thus water, to the intestinal lumen. mucus secretion into the airways. None of these effects are observed. Actually, all of these effects are observed.

constriction of arteries through the epinephrine receptor.

All genes regulated by PKA contain a cis-acting DNA sequence that binds to the phosphorylated form of a transcription factor called: a. c-Jun b. CREB c. β-catenin d. TCF

creb

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 receptor must have a phenylalanine residue in a specific location. c. Ligand binding causes a conformational shift that reveals a binding site for another receptor. d. The ligand has two binding sites for receptors.

d. The ligand has two binding sites for receptors.

What kind of enzyme is the RAS gene product, the Ras protein? a. a phosphodiesterase b. an ATPase c. a kinase d. a GTPase

d. a GTPase

What phosphorylates the tyrosine residues found on docking proteins? a. a G protein coupled receptor b. a cytoplasmic protein-tyrosine kinase c. adaptor proteins d. a receptor protein-tyrosine kinase

d. a receptor protein-tyrosine kinase

Which of the following mechanisms is not used to terminate cytokine signaling and the JAK/STAT pathway? a. receptor internalization b. transcription of SOCS proteins c. dephosphorylation of phosphotyrosine residues d. heterodimerization of cytokine receptors

d. heterodimerization of cytokine receptors

Latent TGFβ is converted to mature TGFβ by: a. phosphorylation b. dephosphorylation c. translocation d. proteolysis

d. proteolysis

In endocrine signaling, ________________________. a. the cell producing the messenger expresses receptors on its surface that can respond to that messenger b. 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 extracellular matrix c. 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 d. the messenger molecules reach their target cells via passage through the bloodstream

d. the messenger molecules reach their target cells via passage through the bloodstream

Activation of a G protein would NOT be considered signal amplification because it:

diffuses to activate a single target, such as adenylyl cyclase.

By what mechanism does PI-3 phosphate promote activation of protein kinase B (PKB)? a. recruiting PKB to the plasma membrane b. recruiting the activating kinase PDK1 to the plasma membrane c. releasing inhibition of the catalytic site by the PH domain d. the first and second answers are correct e. all of the above

e

What could be defined as an organized network of extracellular materials found beyond the immediate vicinity of the plasma membrane? epicellular matrix extracellular matrix extracellular proteins intracellular matrix

extracellular matrix

In addition to activating glycogen phosphorylase in the liver, protein kinase A also activates

gluconeogenesis—the conversion of three-carbon compounds such as pyruvate (see Figure 12-3) to glucose—thus increasing the concentration of glucose in the blood and enhancing the short-term effects of activated PKA.

The tightest attachment between a cell and its extracellular matrix is seen at the site where an epithlial cell is attached to the underlying basement membrane. The specialized adhesive structure found at such a site is called a(n) ____________. tight junction hemidesmosome spot desmosome plasmodesma

hemidesmosome

What substance joins proteoglycans together into gigantic complexes called proteoglycan aggregates? These complexes can occupy very large volumes. hyaluronic acid proteoglycase hyaluronidase fibronectin

hyaluronic acid

In fat cells, activation of adenylyl cyclase leads to: inhibition of catabolism. increased lipolysis. reduced oxygen consumption. All of the answers are correct. None of the answers is correct.

increased lipolysis. Activation of adenylyl cyclase, and thus the increase in the cAMP level, is proportional to the total concentration of Gαs·GTP resulting from the binding of each hormone to its respective receptor.

Sos serves as a GEF (guanine exchange factor) for Ras by: Please choose the correct answer from the following choices, and then select the submit answer button. hydrolyzing ATP. hydrolyzing GTP. phosphorylating it. inducing a conformational change. None of the answers is correct.

inducing a conformational change

What integral membrane protein family made of two membrane-spanning chains (α and β) is involved in attaching cells to their extracellular microenvironment? laminins myosins integrins fibronectins

integrins

Which of the following is cleaved by regulated intramembrane proteolysis (RIP)? a. IkB b. Notch c. IkB and TGFβ d. TGFβ

notch

What is required for complete PKB activation? phosphorylation by PDK1 on its activation site recruitment to the plasma membrane by PI 3-phosphates phosphorylation by PDK2 recruitment to the plasma membrane by interaction with a phosphotyrosine residue All of these are necessary for complete activation.

recruitment to the plasma membrane by interaction with a phosphotyrosine residue

Epidermal growth factor (EGF), as implied, stimulates cell growth. Many cancer cells have elevated levels of the EGF receptor, which means that they will: bind much more EGF. bind EGF with higher affinity. respond to lower levels of EGF. All of the answers are correct. None of the answers is correct

respond to lower levels of EGF

From what cell organelle does the desmotubule appear to be derived? the cell wall of both cells the SER of the two cells the RER of the two cells the Golgi complex of the two cells

the SER of the two cells

Which cell junction prevents the movement of solutes between the cells of an epithelial layer? gap junctions desmosomes tight junctions adherens junctions

tight junctions

When the epidermal growth factor (EGF) receptor is in monomeric form: it has higher than expected kinase activity. its activation loop obscures the kinase domain. it, like rhodopsin, transduces signal until it is triggered. it cannot bind ligand. None of the answers is correct.

ts activation loop obscures the kinase domain.