BIOL351 Cell Biology Cell Signaling

Which of the following mechanisms is not directly involved in inactivating an activated RTK? (a) dephosphorylation by serine/threonine phosphatases (b) dephosphorylation by protein tyrosine phosphatases (c) removal of the RTK from the plasma membrane by endocytosis (d) digestion of the RTK in lysosomes

(a)

Which of the following statements is true? (a) Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior. (b) To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol. (c) A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response (d) Any foreign substance that binds to a receptor for a normal signal molecule will always induce the same response that is produced by that signal molecule on the same cell type.

(a) Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.

Which of the following statements about molecular switches is false? (a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off. (b) Protein kinases transfer the terminal phosphate from ATP onto a protein.(c) Serine/threonine kinases are the most common types of protein kinase.(d) A GTP-binding protein exchanges its bound GDP for GTP to become activated.

(a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off.

Which of the following statements about molecular switches is false? (a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off. (b) Protein kinases transfer the terminal phosphate from ATP onto a protein. (c) Serine/threonine kinases are the most common types of protein kinase. (d) A GTP-binding protein exchanges its bound GDP for GTP to become activated.

(a), removes the phosphate from switch proteins

Which of the following statements is true? (a) Because endocrine signals are broadcast throughout the body, all cells will respond to the hormonal signal. (b) The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling. (c) Paracrine signaling involves the secretion of signals into the bloodstream for distribution throughout the organism. (d) The axons of neurons typically signal target cells using membrane-bound signaling molecules that act on receptors in the target cells.

(b)

Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells. Which of the following statements is false? (a) Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine, whereas skeletal muscle cells contract. (b) Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family. (c) Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways. (d) Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal.

(b), Heart muscle and salivary gland cells have receptor proteins, whereas skeletal muscles have a different receptor protein

Which of the following statements is true? (a) MAP kinase is important for phosphorylating MAP kinase kinase. (b) PI 3-kinase phosphorylates a lipid in the plasma membrane. (c) Ras becomes activated when an RTK phosphorylates its bound GDP to create GTP. (d) STAT proteins phosphorylate JAK proteins, which then enter the nucleus and activate gene transcription.

(b), These phosphorylated lipids serve as dockingsites for specific intracellular signaling proteins, which relocate from the cytosol to the plasma membrane, where theycan activate one another.

The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________________. (a) activating a G protein. (b) activating a receptor tyrosine kinase. (c) diffusing into cells and stimulating the cyclase directly. (d) activating an intracellular protein kinase.

(c)

A protein kinase can act as an integrating device in signaling if it___________________.(a) phosphorylates more than one substrate.(b) catalyzes its own phosphorylation.(c) is activated by two or more proteins in different signaling pathways.(d) initiates a phosphorylation cascade involving two or more protein kinases.

(c) Integrating devices are able to relay signals from more than one signaling pathway.Being activated by two or more proteins in different signaling pathways allows a kinase(or any other signaling molecule) to be affected by more than one upstream signal.Choices (a), (b), and (d) affect the output signal that a kinase is able to produce, not itsability to integrate upstream signals from more than one signaling pathway.

Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen. Which of the following statements is false? (a) A constitutively active mutant form of PKA in skeletal muscle cells would lead to a decrease in the amount of unphosphorylated phosphorylase kinase. (b) A constitutively active mutant form of PKA in skeletal muscle cells would not increase the affinity of adrenaline for the adrenergic receptor.(c) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glucose available. (d) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available

(d)

Which of the following statements about G-protein-coupled receptors (GPCRs) is false? (a) GPCRs are the largest family of cell-surface receptors in humans. (b) GPCRs are used in endocrine, paracrine, and neuronal signaling. (c) GPCRs are found in yeast, mice, and humans. (d) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.

(d) Although it is true that many types of ligands can bind to and activate GPCRs, allGPCRs have a similar structure with seven transmembrane domains.

Which of the following statements about G-protein-coupled receptors (GPCRs) is false? (a) GPCRs are the largest family of cell-surface receptors in humans. (b) GPCRs are used in endocrine, paracrine, and neuronal signaling. (c) GPCRs are found in yeast, mice, and humans. (d) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.

(d) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.

Which of the following statements is false? (a) Nucleotides and amino acids can act as extracellular signal molecules.(b) Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription. (c) Some signal molecules are transmembrane proteins. (d) Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids.

(d), NO binds to and activates the target protein guanylyl cyclase, which ends up catalyzing production of cyclic GMP from GTP; regulating the activity of specific proteins to cause smooth muscle cells to relax

Which of the following statements is false? A. Serine/threonine protein kinases phosphorylate extracellular proteins on serines and/or threonines. B. Tyrosine protein kinases phosphorylate intracellular proteins on tyrosines. C. Serine/threonine protein kinases phosphorylate intracellular proteins on serines and/or threonines.

A. Serine/threonine protein kinases phosphorylate extracellular proteins on serines and/or threonines.

A target cell can respond quickly to an extracellular signal if: A. the cell does not require a receptor for the signal molecule. B. the response does not require target cell proteins to be altered. C. the response does not require new gene transcription or new protein synthesis.

C. the response does not require new gene transcription or new protein synthesis.

Ca2+ can trigger biological effects in cells because an unstimulated cell has an extremely __________________ concentration of free Ca2+ in the cytosol, compared with its concentration in the __________________ space and in the__________________, creating a steep electrochemical gradient. When Ca2+ enters the cytosol, it interacts with Ca2+-responsive proteins such as __________________, which also binds diacylglycerol, and __________________, which activates CaM-kinases.adenylyl cyclase endoplasmic reticulum nuclear average extracellular peroxisomeCa2+ high phospholipase Ccalmodulin intracellular protein kinase A colorful low protein kinase C

Ca2+ can trigger biological effects in cells because an unstimulated cell has an extremelylow concentration of free Ca2+ in the cytosol, compared with its concentration in theextracellular space and in the endoplasmic reticulum, creating a steep electrochemicalgradient. When Ca2+ enters the cytosol, it interacts with Ca2+-responsive proteins such asprotein kinase C, which also binds diacylglycerol, and calmodulin, which activatesCaM-kinases.

Which of the following statements about molecular switches is false? (a) Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off. (b) Protein kinases transfer the terminal phosphate from ATP onto a protein. (c) Serine/threonine kinases are the most common types of protein kinase. (d) A GTP-binding protein exchanges its bound GDP for GTP to become activated.

Choice (a) is false. GTP-binding proteins themselves hydrolyze their bound GTP to GDP,using their own intrinsic GTPase activity.

Which of the following statements is true? (a) Because endocrine signals are broadcast throughout the body, all cells will respond to the hormonal signal. (b) The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling. (c) Paracrine signaling involves the secretion of signals into the bloodstream for distribution throughout the organism. (d) The axons of neurons typically signal target cells using membrane-bound signaling molecules that act on receptors in the target cells.

Choice (b) is correct. Choice (a) is not true because only the cells with a receptor for thehormone will respond to the signal. Choice (c) is not true because paracrine signalinginvolves signaling in a more local fashion, unlike endocrine signaling where signals aresent through the bloodstream. Choice (d) is untrue because axons typically signal usingdiffusible neurotransmitters that are released at the synapse.

Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells. Which of the following statements is false? (a) Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine, whereas skeletal muscle cells contract. (b) Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family. (c) Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways. (d) Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal.

Choice (b) is not true. Only skeletal muscle cells express an acetylcholine receptor that belongs to the transmitter-gated ion channel family; salivary gland cells and heart muscle cells express a different receptor. The other choices are all true.

Figure Q16-61 shows that intracellular signaling pathways can be highly interconnected. Which of the following statements is incorrect? (a) The GPCR and the RTK both activate phospholipase C. (b) Activation of either the GPCR or the RTK will lead to activation of transcriptional regulators.( c) CaM-kinase is only activated when the GPCR is active and not when the RTK is active. (d) Ras is activated only when the RTK is active and not when the GPCR is active.

Choice (c) is incorrect. CaM-kinase is activated by calmodulin, which is ultimately activated by phospholipase C. Either the GPCR or the RTK activates phospholipase C.All the other statements are correct.

Receptor tyrosine kinase signaling pathway examples:

PLC-> diacylglycerol (DAG) -> PKC=-involved in regulating receptor desensitization, modulating membrane structure events, gene transcription, immune responses, cell growth, and learning and memory processes PI 3-kinase-> PK1-> Akt kinase=-Regulates multiple biological processes including cell survival, proliferation, growth, and glycogen metabolism

All members of the steroid hormone receptor family __________________. (a) are cell-surface receptors. (b) do not undergo conformational changes. (c) are found only in the cytoplasm. (d) interact with signal molecules that diffuse through the plasma membrane.

Choice (d) is correct. All members of the steroid hormone receptor family areintracellular proteins [thus choice (a) is not correct] that interact with signal moleculesthat can diffuse through the plasma membrane. Once activated, steroid hormone receptorsregulate gene transcription in the nucleus [choice (c)]. The binding of the signal moleculeinduces a large conformational change in the receptor protein [choice (b)]. Thisconformational change activates the steroid hormone receptors, allowing them to promoteor inhibit the transcription of the appropriate genes.

Akt promotes the survival of many cells by affecting the activity of Bad and Bcl2,as diagrammed in Figure Q16-58.Figure Q16-58Which of the following statements is false? (a) In the presence of a survival signal, Akt is phosphorylated. (b) In the absence of a survival signal, Bad inhibits the cell-death inhibitor protein Bcl2. (c) In the presence of a survival signal, the cell-death inhibitory protein Bcl2 is active. (d) In the absence of a survival signal, Bad is phosphorylated.

Choice (d) is false. Bad is phosphorylated in the presence of a survival signal. When the survival signal is not present, Bad binds to the cell-death inhibitor protein Bcl2, promoting cell death. All the other statements are correct.

True/false A cell will have only one type of receptor and a few copies of it

FALSE A cell will have many different types of receptors and hundreds to thousands of copies each one-allows cells to be sensitive to many signals-Can drive a cell to survive, grow and divide, differentiate, or even to die

A given steroid hormone usually regulates the same sets of genes in different types of target cells. T/F?

False

Each type of extracellular signal molecule induces a similar response in different target cells. T/F?

False

GPCRs exist in prokaryotes T/F

False--however structurally similar proteins like bacteriorhodopsin function in similar ways to GPCRs

When GTP binds to a protein, it can activate it OR inhibit it T/F

False--it can only activate it

cyclic AMP phosphodiesterase converts cyclic AMP to regular AMP relatively slowly T/F

False--it does it very rapidly

the number of different types of extracellular signals is greater than the different types of receptors that they can act on T/F

False--there are more types of receptors than extracellular signals; one signal can act on different types of receptors

G-protein-coupled receptor signaling pathway examples:

G protein-> adenylyl cyclase-> cyclic AMP-> PKA=-Involved in regulating glycogen, sugar, and lipid metabolism G protein-> IP3-> Ca2+->calmodulin->CaM-kinase=-involved in nervous systems such as nerve cell protection, and learning and memory processes.

Ion-channel-coupled receptor signaling pathway examples:

Skeletal muscle cells have receptors for acetylcholine, which is the primary neurotransmitter released by motor neurons -When acetylcholine binds to the receptors on the skeletal muscle cell, the ion channels open, causing sodium and potassium ions to enter the cell and subsequently launches a sequence of events that results in contraction of the cell

True/false Signals acting together can have larger effects thane one signal acting alone

TRUE

True/false The same signal molecules can induce different responses in different target cells

TRUE EX Acetylcholine's (a neurotransmitter) effect on heart, salivary gland, and skeletal muscle cells

Some dissolved gases cross the plasma membrane and activate intracellular enzymes directly. T/F?

True

for every activation step in the pathway there must be an inactivation step T/F

True

phosphorylation of a protein can activate it OR inhibit it T/F

True

To inactivate RTK

a tyrosine phosphatase enzyme removes the phosphates form the tyrosine on the activated receptor