BIOC 384 Exam 3

Increased serum glucose levels leads to insulin secretion from pancreatic b cells. Put the following steps in the correct order to explain the biochemical processes that are required for this response. 1. Activation of voltage-gated Ca2+ channels and import of Ca2+. 2. Stimulation of glucokinase enzyme levels following glucose import. 3. ATP inhibits K+ channels leading to membrane depolarization. 4. Insulin increases in blood and stimulates insulin signaling pathways. 5. Ca2+ stimulates insulin vesicle fusion with plasma membrane. 6. Increased flux through glycolysis leads to increased ATP synthesis.

2. Stimulation of glucokinase enzyme levels following glucose import. 6. Increased flux through glycolysis leads to increased ATP synthesis. 3. ATP inhibits K+ channels leading to membrane depolarization. 1. Activation of voltage-gated Ca2+ channels and import of Ca2+. 5. Ca2+ stimulates insulin vesicle fusion with plasma membrane. 4. Insulin increases in blood and stimulates insulin signaling pathways.

Which of the THREE statements explain why it makes sense that caspase enzymes like CASP3 function as executioners in the cell death pathway? 1. Caspases have a dispensable cysteine residue in the active site that is often acetylated. 2. Caspases are catalytic enzymes and can do a lot of damage in a short period of time. 3. Caspases are able use H2O as a substrate, which is totally unique to killer enzymes. 4. Caspases function as a pure homodimer, which provides a unique subunit organization. 5. Caspases have preferred cleavage sites and degrade key proteins to quickly kill cells. 6. Caspases need to be activated by cleavage and are easily stored in cells as inactive zymogens.

2. Caspases are catalytic enzymes and can do a lot of damage in a short period of time. 5. Caspases have preferred cleavage sites and degrade key proteins to quickly kill cells. 6. Caspases need to be activated by cleavage and are easily stored in cells as inactive zymogens.

What is Cyclic GMP target protein? 1. Calcium channel protein 2. Protein kinase G 3. Protein kinase A 4. Calmodulin 5. Protein kinase C

2. Protein kinase G

What is Calcium target protein? 1. Calcium channel protein 2. Protein kinase G 3. Protein kinase A 4. Calmodulin 5. Protein kinase C

4. Calmodulin

Which of the following reactions would depend only on substrate availability? A. 3-phosphoglycerate à 2-phosphoglycerate B. Glucose + ATP à Glucose-6-phosphate + ADP C. Phosphoenolpyruvate + ADP à Pyruvate + ATP D. 1,3-BPG + ADP à 3-Phosphoglycerate + ATP E. None of these answers are correct.

A. 3-phosphoglycerate à 2-phosphoglycerate

Which amino acid is NOT a target for kinases? A. Asp B. Thr C. Ser D. Tyr

A. Asp

Both epinephrine (a tyrosine derivative) and glucagon (a peptide hormone) increase glucose export from the liver into the bloodstream. Each ligand binds a different receptor, but both lead to an activation of PKA. How does this happen? A. Both receptors bind and activate the same Gα subunit, Gsα, which indirectly leadsto PKA activation. B. Both receptors bind directly to and activate PKA after the Gsα protein dissociatesfrom the receptor. C. Each activated receptor interacts with a unique GTP binding protein that activates PKA. D. The receptors for the two ligands interact before binding to the heterotrimeric G proteins.

A. Both receptors bind and activate the same Gα subunit, Gsα, which indirectly leadsto PKA activation.

Whether a G alpha subunit is active or inactive depends on which guanine nucleotide is bound to it. Binding of GDP or GTP results in the protein switching between two conformational states. Which of the following answers best describes the structural changes that occur in a G alpha subunit due to guanine nucleotide binding? A. Dissociation of GDP for GTP with the G alpha subunit structurally shifts the switch II helix region, allowing for the association of G alpha with its effector proteins, such as adenylate cyclase. B. Epinephrine directly binds and activates G alpha to allow the subunit to bind to an effector protein. C. Phosphorylation of GDP to GTP by the G alpha subunit moves the switch II helix region from binding to G beta/gamma to binding effectors like adenylate cyclase. D. The helical region of G alpha, called switch II, which interacts with G beta/gamma in the inactive state, is brought into the interior of the G alpha protein, reducing contact with G beta/gamma. This permits G alpha interaction with effector proteins, like adenylate cyclase, since the switch II region is now buried.

A. Dissociation of GDP for GTP with the G alpha subunit structurally shifts the switch II helix region, allowing for the association of G alpha with its effector proteins, such as adenylate cyclase.

What two properties of glucokinase ensure that glucose is properly apportioned into liver cells? A. Glucokinase has 100-fold higher Km than hexokinase and is not inhibited by glucose-6-phosphate. B. Glucokinase has 100-fold lower Km than hexokinase and is allosterically inhibited by glucose. C. Hexokinase has 100-fold lower Km than glucokinase and is inhibited by glucose-6-phosphate. D. Glucokinase has 100-fold lower Km than hexokinase and is not inhibited by glucose-6-phosphate. E. Glucokinase is stimulated by ATP and glucokinase is expressed only in liver cells.

A. Glucokinase has 100-fold higher Km than hexokinase and is not inhibited by glucose-6-phosphate.

Which of the following statements best describes the effect of ADP on the activity of PFK-1? A. High concentrations of ADP block the inhibitory effect of ATP by competing for the same allosteric site on PFK-1. B. High concentrations of ADP enhance the activation of PFK-1 by fructose-2,6-bisphosphate by stabilizing the allosteric site. C. High concentrations of ADP block the synthesis of ATP, which reduces inhibition of PFK-1. D. High concentrations of ADP lead to increased formation of fructose-2,6-bisphosphate and enhanced activity of PFK-1.

A. High concentrations of ADP block the inhibitory effect of ATP by competing for the same allosteric site on PFK-1.

Interaction of glucocorticoid receptors with which of the following prevents binding to glucocorticoid response elements (GREs)? A. Hsp90 B. p60 C. p50 D. Annexin I gene

A. Hsp90

What is the function of growth factor receptor-bound 2 (GRB2) protein in RTK signaling? A. It is an adaptor protein that binds to phosphotyrosine residues in RTKs and also binds to GEF proteins. B. It is an adaptor protein that binds to phosphoserine residues in IRSs and to GEF proteins like PI-3K. C. It is a tyrosine kinase protein that phosphorylates arginine residues in PI-3K and in phospholipase C. D. It is a survival protein that binds to cysteine proteases and inhibits their auto-cleavage by TRADD. E. It is an adaptor protein that binds to G proteins like Ras and GSa and also to MAPK, Raf, and ERK.

A. It is an adaptor protein that binds to phosphotyrosine residues in RTKs and also binds to GEF proteins.

Long-term activation by nuclear receptors differs from the more transient membrane receptor signaling for what reason? A. Long-term activation occurs by nuclear receptors activating sets of genes, while membrane receptors involve small second messenger molecules responding quickly, as their signaling occurs by activation of kinases, phosphatases, and other enzymes already expressed in the cell. B. Receptor-mediated signaling takes longer to reverse the phosphorylation caused by kinases, while nuclear protein expression is much faster. C. Steroid receptors are antagonistic to most GPCR signaling. D. It takes longer for the steroid to diffuse through the cell, while membrane receptor ligands do not require translocation into the cell.

A. Long-term activation occurs by nuclear receptors activating sets of genes, while membrane receptors involve small second messenger molecules responding quickly, as their signaling occurs by activation of kinases, phosphatases, and other enzymes already expressed in the cell.

Which of the following is correct about the link between Ras and cancer? A. Mutated Ras is an oncogene. B. Ras is considered a tumor suppressor gene. C. The role of Ras in cancer is due to a recessive mutation. D. Mutant Ras has enhanced GTPase activity.

A. Mutated Ras is an oncogene.

One subtype of breast cancer involves the human epidermal growth factor receptor 2 gene (EGF receptor). One in every five breast cancers has a mutation in this gene. Understanding that this is a growth factor receptor gene, which of the answer choices best describes how this type of cancer develops? A. Mutations that activate the kinase portion of the receptor result in a receptor that is constantly phosphorylated. This causes constitutive activation of downstream signaling and the resulting cell growth and proliferation. B. Mutations that block the receptor from functioning will block cell growth, indicating that this is a loss-of-function gene. C. Interactions of the mutated receptor, which activates protein kinases, will not impact tumor growth because the ligand cannot bind to the receptor. D. Mutations in the intracellular domain of the receptor will cause Akt to bind without further signaling and regulation of cell apoptotic processes.

A. Mutations that activate the kinase portion of the receptor result in a receptor that is constantly phosphorylated. This causes constitutive activation of downstream signaling and the resulting cell growth and proliferation.

Which of the following is not a parameter that governs the cell-specific physiological responses controlled by nuclear receptors? A. Organism-wide expression of coregulatory proteins B. Cell-specific expression of nuclear receptors C. Differential accessibility of target gene DNA sequences D. Localized bioavailability of ligands

A. Organism-wide expression of coregulatory proteins

Which enzyme's activity is controlled by the levels of glucose-6-P and fructose-6-P in the cell? A. Phosphoglucoisomerase B. Hexokinase C. Aldolase D. Phosphofructokinase-1

A. Phosphoglucoisomerase

Which of the following is least likely to affect the metabolic flux of a metabolic pathway? A. Steady-state substrate concentrations B. Formation of a multienzyme complex by pathway enzymes C. Large influx of substrate D. Decoupling of a favorable and an unfavorable reaction

A. Steady-state substrate concentrations

What two pathways require enzymatic modification of phosphatidylinositol-4,5-bisphosphate? A. The phospholipase C signaling pathway; and the PI-3K pathway that uses PH domain binding to PIP3. B. The MAPK pathway that uses PIP3 to generate DAG and IPs; and PI-3K to activate PTEN signaling. C. The insulin pathway that uses PIP2 as a docking site for SH2 domains; and adenylate cyclase signaling. D. The phospholipase C pathway that uses PIP3 as a docking site for PH domains; and TNF signaling. E. None of these answers are correct.

A. The phospholipase C signaling pathway; and the PI-3K pathway that uses PH domain binding to PIP3.

Glycolysis is an anaerobic / aerobic pathway (a), which metabolizes dietary hexose sugars such as fructose / lactase (b) to yield 2 net ATP, 2 FADH2 / 2 NADH (c) and 2 pyruvate per mole of hexose sugar. When energy charge is low, flux through glycolysis is stimulated / inhibited (d) by the allosteric effector ATP / AMP (e) through activation of phosphofructokinase I / hexokinase I (f) activity.

A. a) anaerobic, b) fructose, c) 2 NADH, d) stimulated, e) AMP, f) phosphofructokinase I

Which of the following first messengers is unique because it is not water soluble and does not bind directly to a membrane receptor? A. estradiol B. nitric oxide C. acetylcholine D. epinephrine

A. estradiol

Which enzyme can be used in the production of HFCS to convert glucose to fructose in a single step? A. glucose isomerase B. glucose dehydrogenase C. glucose oxidase D. glucose epimerase

A. glucose isomerase

Sucrose, maltose, and lactose are common dietary disaccharides. Their monosaccharide components are substrates for the glycolytic pathway, but some must participate in additional reactions before they can act as substrates for a glycolytic enzyme. As a result, all do not enter glycolysis at the same step. In muscle cells, which enzyme would act as the rate-limiting step to regulate entry of products from all three dietary disaccharides into glycolysis? A. phosphofructokinase-1 B. hexokinase C. aldolase D. phosphoglucose isomerase

A. phosphofructokinase-1

Which of the following first messengers is unique because it is hydrophobic and binds to a soluble receptor protein inside cells? A. progesterone B. epinephrine C. glucagon D. insulin E. acetylcholine

A. progesterone

Which of the following statements correctly describe the properties of glucose and fructose? A.Glucose can form furanose and pyranose ring structures, while fructose can only form a furanose ring. B.Glucose is found in at least three common disaccharides found in nature, while fructose is a component of only one. C.Glucose and fructose are both reducing sugars. D.Glucose and fructose are both hexose sugars.

A.Glucose can form furanose and pyranose ring structures, while fructose can only form a furanose ring. B.Glucose is found in at least three common disaccharides found in nature, while fructose is a component of only one. D.Glucose and fructose are both hexose sugars.

Why does lactase deficiency lead to the retention of lactose within the small intestine and prevent transport across the intestinal lumen? A.Lactose is a polar molecule and cannot cross the intestinal membrane without a transport protein. B.Bacteria in the small intestine ferment lactose and produce gas. C.Transport proteins in the intestinal lumen are specific for monosaccharides. D.Excess lactose osmotically increases water flow into the small intestine.

A.Lactose is a polar molecule and cannot cross the intestinal membrane without a transport protein. C.Transport proteins in the intestinal lumen are specific for monosaccharides.

Choose the correct statements about the function and activity of arrestin. A.PKA phosphorylation also modifies GPCR, leading to arrestin binding to the receptor for endosomal transport. B.Arrestin phosphorylation of the GPCR leads to a loss of receptor interaction with G proteins. C.Arrestin facilitates protein transport, which prevents a receptor from reassociating with the G protein complex. D.Arrestin directly binds the G proteins after phosphorylation, limiting the interaction of the G proteins with their GPCR.

A.PKA phosphorylation also modifies GPCR, leading to arrestin binding to the receptor for endosomal transport. C.Arrestin facilitates protein transport, which prevents a receptor from reassociating with the G protein complex.

Insulin is released by the beta islets of the pancreas after a meal when glucose levels are high. Released as a peptide, insulin binds to a unique class of receptors that lead to the reduction of blood sugar levels. The insulin receptor has a tyrosine kinase intracellular domain. However, unlike many other similar single transmembrane receptors with a tyrosine kinase activity (such as growth factor receptors), the insulin receptor is a crosslinked dimer in the resting state made of two alpha and two beta strands (heterotetramer).Which of the following statements describe how the insulin receptor is activated? A.The intracellular domain of the insulin receptor, specifically the tyrosines, must be phosphorylated to recruit the intracellular signaling partners. B.Insulin binding to the insulin receptor induces a conformational change that stimulates tyrosine autophosphorylation of the beta subunits. C.Following insulin binding, the receptor will bind with another receptor as long as only one insulin peptide is bound. This is an example of a negative feedback cooperative regulation. D.An insulin receptor has two binding sites for insulin, and each ligand is required to begin autophosphorylation.

A.The intracellular domain of the insulin receptor, specifically the tyrosines, must be phosphorylated to recruit the intracellular signaling partners. B.Insulin binding to the insulin receptor induces a conformational change that stimulates tyrosine autophosphorylation of the beta subunits.

Infants express the enzyme lactase in their intestines to metabolize lactose. How many net ATP can be generated from lactose under anaerobic conditions by infants with high levels of lactase? A. 2 net ATP B. 4 net ATP C. 6 net ATP D. 32 net ATP E. 64 net ATP

B. 4 net ATP

Which of the following is NOT a primary mechanism for affecting catalytic efficiency? A. Proteolytic processing B. Cellular compartmentalization C. Covalent modification D. Binding of regulatory molecules

B. Cellular compartmentalization

Which of the following relationships is correctly defined? A. D-Glucose and L-Glucose are anomers B. D-Ribose and D-Xylose are epimers C. D-Ribose and D-Xylose are isomers D. D-Glucose and D-Mannose are anomers

B. D-Ribose and D-Xylose are epimers

Which of the following activates a zymogen? A. Trypsinogen B. Enterokinase C. Chymotrypsinogen D. Pepsinogen

B. Enterokinase

Which glycolytic enzyme is responsible for decreased flux through glycolysis during exercise when NAD+ levels are limiting owing to defects in lactate dehydrogenase? A. Pyruvate kinase B. Glyceraldehyde-3P dehydrogenase C. Hexokinase D. Enolase E. Lactase

B. Glyceraldehyde-3P dehydrogenase

How would the oxygen saturation of hemoglobin in an individual with bisphosphoglycerate mutase deficiency compare to that in an unaffected individual? A. Hemoglobin oxygen saturation would be decreased in the erythrocytes of individuals with bisphosphoglycerate mutase deficiency as compared to a normal individual. B. Hemoglobin oxygen saturation would be increased in the erythrocytes of individuals with bisphosphoglycerate mutase deficiency as compared to a normal individual. C. Hemoglobin oxygen saturation could be increased or decreased in the erythrocytes of individuals with bisphosphoglycerate mutase deficiency as compared to a normal individual. The effect of this deficiency would depend on glycolytic flux. D. Hemoglobin oxygen saturation would be the same in the erythrocytes of individuals with bisphosphoglycerate mutase deficiency as compared to a normal individual.

B. Hemoglobin oxygen saturation would be increased in the erythrocytes of individuals with bisphosphoglycerate mutase deficiency as compared to a normal individual.

Which of the following is the downstream signaling protein for the TRADD-associated complex in the cell survival path of TNF signaling? A. NIK B. IKK C. RIP D. TRAF2

B. IKK

Name the enzymes that catalyze the two substrate level phosphorylation reactions in glycolysis. A. Hexokinase and phosphofructokinase-1 B. Pyruvate kinase and phosphoglycerate kinase C. Glyceraldehyde-3-phosphate dehydrogenase and pyruvate kinase D. Phosphoglycerate kinase and phosphofructokinase-1 E. None of these answers are correct.

B. Pyruvate kinase and phosphoglycerate kinase

TNF-alpha activation can lead to a cell survival mechanism as well as cell death. In the survival portion of TNF receptor signaling, TRADD recruits two adaptor proteins that function to initiate a downstream phosphorylation cascade. What is the role for one of these adaptor proteins called TNF receptor-associated factor 2 (TRAF2)? A. TRAF2 competes with the protein kinase RIP to block the phosphorylation of IKK and deactivates NFkB signaling to the nucleus to enhance anti-apoptotic gene production. B. TRAF2 recruits and activates NIK (NFkB inducing kinase) to the TNF receptor complex where NIK phosphorylates IKK, leading to the active transcription of anti-apoptotic genes. C. The TRADD-TRAF2 complex binds and inhibits procaspase 8 via FADD interactions. D. TRADD-TRAF2 binds both NIK and RIP kinases to produce a phosphorylated and inactive NFkB, which blocks pro-apoptotic pathways, resulting in a cell survival result.

B. TRAF2 recruits and activates NIK (NFkB inducing kinase) to the TNF receptor complex where NIK phosphorylates IKK, leading to the active transcription of anti-apoptotic genes.

What two pathways require enzymatic modification of phosphatidylinositol-4,5-bisphosphate? A. The MAPK pathway that uses PIP3 to generate DAG and IPs; and PI-3K to activate PTEN signaling. B. The PI-3K pathway that uses PIP3 as a docking site for PH domains; and phospholipase C signaling. C. The PI-3K pathway that uses PIP2 as a docking site for SH3 domains; and phospholipase C signaling. D. The phospholipase C pathway that uses PIP3 as a docking site for PH domains; and GPCR signaling. E. The TNF pathway that uses PIP2 as a docking site for SH2 domains; and protein kinase C signaling.

B. The PI-3K pathway that uses PIP3 as a docking site for PH domains; and phospholipase C signaling.

Glyceraldehyde-3-phosphate dehydrogenase catalyzes the phosphorylation of glyceraldehyde-3-phosphate, but unlike other glycolytic reactions, it does not require energy investment from ATP. This reaction occurs in two stages: oxidation/reduction and phosphorylation. Why is the oxidation/reduction reaction necessary to make phosphorylation favorable? A. The oxidation/reduction reaction is for the substrate to bind to the enzyme. B. The oxidation/reduction reaction is necessary to form an intermediate with a large free energy of hydrolysis. C. The oxidation/reduction reaction is necessary to oxidize phosphate, allowing addition to the substrate. D. The oxidation/reduction reaction is necessary to produce NADH, which is required for ATP synthesis.

B. The oxidation/reduction reaction is necessary to form an intermediate with a large free energy of hydrolysis.

Kinase enzymes phosphorylate proteins in order to control their catalytic efficiency. Which of the following amino acids is targeted for phosphorylation by kinases, and what type of enzyme removes the phosphate to reverse the regulation? A. Serine; phosphorylase B. Tyrosine; phosphatase C. Asparagine; phosphatase D. Threonine; hydratase E. Glutamate; phosphatase

B. Tyrosine; phosphatase

Which statement explains why glucose phosphorylation could not occur without ATP investment? A. Without ATP investment, glucose would not become "trapped" in the cell and could easily be transported out as blood glucose levels decrease. This transport would reduce the amount of glucose available for some organs. B. Without ATP investment, one or both of the substrates would need to exceed the solvent capacity of the cell for glucose phosphorylation to occur. C. Without ATP investment it would be impossible to regulate the entry of glucose into glycolysis. D. Without ATP investment in stage I of glycolysis, the concentration of ATP would become too high and would inhibit phosphofructokinase, leading to inhibition of the entire glycolytic pathway.

B. Without ATP investment, one or both of the substrates would need to exceed the solvent capacity of the cell for glucose phosphorylation to occur.

You are hiking the finger rock trail in the Catalina mountains and come across a rattlesnake crossing the trail, which activates a physiological stress response. Choose the answer below that correctly identifies the a) hormone, b) a receptor that is activated by the hormone in part a, and c) the target enzyme that is activated in the downstream pathway identified by parts a + b A. a) glucagon; b) a1 adrenergic receptor; c) adenylate cyclase B. a) epinephrine; b) b2 adrenergic receptor; c) adenylate cyclase C. a) epinephrine; b) b2 adrenergic receptor; c) phospholipase c D. a) glucagon; b) glucagon receptor; c) phospholipase c E. a) epinephrine; b) a1 adrenergic receptor; c) adenylate cyclase

B. a) epinephrine; b) b2 adrenergic receptor; c) adenylate cyclase

Which of the following is not a biochemical process affecting the bioavailability of enzymes? A. RNA processing B. binding of a competitive inhibitor C. protein synthesis and degradation D. RNA synthesis

B. binding of a competitive inhibitor

Which of the following statements is true concerning the role of cGMP in vasodilation? A. Vasodilation is increased by increased activity of cGMP phosphodiesterase. B. cGMP is a secondary messenger that acts on protein kinase G. C. Increased cGMP leads to increased NO, which serves as a secondary messenger for vasodilation. D. Sildenafil prolongs NO-mediated vasodilation by stimulating production of cGMP.

B. cGMP is a secondary messenger that acts on protein kinase G.

A __________ inhibitor is a type of irreversible inhibitor. A. uncompetitive B. covalent C. competitive D. mixed

B. covalent

Acetylcholinesterase is an important enzyme in the nervous system. Acetylcholinesterase activity is blocked by the nerve agent sarin gas, which forms a covalent bond with a Ser in the active site of the enzyme. Sarin gas is a(n) A. competitive inhibitor B. irreversible inhibitor C. allosteric effector D. reversible inhibitor

B. irreversible inhibitor

Even in the presence of a properly signaling TNF receptor signaling pathway that involves FADD and TRADD, breast cancer cells do not undergo apoptosis in response to TNF-alpha, allowing tumors to grow and metastasize. A close inspection shows that one protein is no longer expressed in these cells. The addition of TNF-alpha leads to TRADD and FADD complexes but does not lead to cell death. Procaspase 3 is expressed and functioning. A western blotting analysis shows that NFkB is expressed, and other studies show that the protein is functioning properly in these cells. What is the most likely cause of resistance to cell death by TNF-alpha in breast cancer cells? A. inactivation of IKK kinases B. loss or mutational inactivation of caspase 8 C. overexpression of CASP3 D. loss of NFkB interacting p50

B. loss or mutational inactivation of caspase 8

A hydrophobic environment is necessary for optimal activity of phosphoglycerate kinase A. to prevent early release of the substrates before the reaction is complete. B. to prevent hydrolysis of 1,3-bisphosphoglycerate. C. for both substrates to bind to the active site. D. for the positioning of the substrates within the active site.

B. to prevent hydrolysis of 1,3-bisphosphoglycerate.

Along with other similar symptoms, both deficiencies can also result in reduced lactate levels during exercise. In order to distinguish between these two disorders, a physician could test the patient's lactate levels during exercise before and after administering glycerol. What would be the expected results if this test were performed? A.Lactate levels would be low after intense exercise and would increase after glycerol was administered if the patient has a deficiency in lactate dehydrogenase. B.Lactate levels would be low after intense exercise and would not increase after glycerol was administered if the patient has a deficiency in lactate dehydrogenase. C.Lactate levels would be low after intense exercise and would not increase after glycerol was administered if the patient has a deficiency in muscle phosphofructokinase-1. D.Lactate levels would be low after intense exercise and would increase after glycerol was administered if the patient has a deficiency in muscle phosphofructokinase-1.

B.Lactate levels would be low after intense exercise and would not increase after glycerol was administered if the patient has a deficiency in lactate dehydrogenase. D.Lactate levels would be low after intense exercise and would increase after glycerol was administered if the patient has a deficiency in muscle phosphofructokinase-1.

Tasting involves many different cell-signaling processes that ultimately generate nerve signals transduced by membrane depolarization. Sweet tastes result in PIP2 hydrolysis, while salty tastes allow sodium ions to directly alter the membrane potential. What can you deduce about the signaling mechanisms for sweet and salty? A.Sweet ligands bind to and close sodium channels, which starts a membrane potential. B.Sweet utilizes the GPCR signaling pathway, activating phospholipase C. C.Sweet and salty signaling pathways use the same taste receptor molecule, but with different efficacy on the sweet and salty taste center in the brain. D.Sodium ions directly enter the cells, indicating the signal is transduced by an ion channel.

B.Sweet utilizes the GPCR signaling pathway, activating phospholipase C. D.Sodium ions directly enter the cells, indicating the signal is transduced by an ion channel.

Glycolytic reactions can either be described as reversible or irreversible. Looking at all 10 reactions in glycolysis, what conclusions can you make about irreversible reactions in general? A.If the reaction involves ATP, it is an irreversible reaction. B.They operate far from equilibrium. C.The enzymes that catalyze these reactions are not shared in opposingpathways (i.e., glycolysis and gluconeogenesis). D.The activity of the enzymes that catalyze irreversible reactions can be increasedor decreased.

B.They operate far from equilibrium. C.The enzymes that catalyze these reactions are not shared in opposingpathways (i.e., glycolysis and gluconeogenesis). D.The activity of the enzymes that catalyze irreversible reactions can be increasedor decreased.

Why would mutation of a tyrosine residue to glutamate in the intracellular portion of a growth factor receptor lead to increased tumor formation? A.This amino acid substitution would convert the protein from poorly water soluble to charged and water soluble. B.Unlike tyrosine, a glutamate will leave the receptor "constitutively" active and no longer responsive to the phosphatases that shut off such signaling. C.Loss of the tyrosine would mean phosphorylation would not occur, thus blocking the inhibiting action of these receptors. D.A receptor with a glutamate in place of a tyrosine is a "phosphomimetic." That is, the protein mimics the phosphorylated state of tyrosine.

B.Unlike tyrosine, a glutamate will leave the receptor "constitutively" active and no longer responsive to the phosphatases that shut off such signaling. D.A receptor with a glutamate in place of a tyrosine is a "phosphomimetic." That is, the protein mimics the phosphorylated state of tyrosine.

Structure-based drug design strategies often devise competitive inhibitors that bind to certain enzyme active sites. For example, saquinavir and indinavir are designed HIV protease inhibitors that bind to the aspartate protease enzyme of HIV, which is required for the virus to produce functional proteins for further HIV infection. Which of the following statements are true about saquinavir and indinavir? A.Increasing concentrations of indinavir or saquinavir would result in a change in the vmax of the aspartate protease enzyme reaction. B.Very high local concentrations of proteins with Phe-Pro or Tyr-Pro peptide bonds would reduce the effectiveness of saquinavir and indinavir in limiting HIV's infectivity of new cells. C.Saquinavir and indinavir both have a component that mimics the natural Phe-Pro dipeptide substrate of aspartate protease. D.The removal of the phenyl ring (six-membered carbon ring containing three double bonds and no attached functional groups) on indinavir and saquinavir would likely affect their inhibitory activity.

B.Very high local concentrations of proteins with Phe-Pro or Tyr-Pro peptide bonds would reduce the effectiveness of saquinavir and indinavir in limiting HIV's infectivity of new cells. C.Saquinavir and indinavir both have a component that mimics the natural Phe-Pro dipeptide substrate of aspartate protease. D.The removal of the phenyl ring (six-membered carbon ring containing three double bonds and no attached functional groups) on indinavir and saquinavir would likely affect their inhibitory activity.

Which state of glycogen phosphorylase gives the enzyme its highest activity? A. ubiquitinated glycogen phosphorylase B. nonphosphorylated glycogen phosphorylase C. methylated glycogen phosphorylase D. phosphorylated glycogen phosphorylase

D. phosphorylated glycogen phosphorylase

Once insulin has bound the α subunit of the insulin receptor, the β subunit of the receptor can bind to an insulin receptor substrate (IRS) protein, which acts as a membrane scaffold. What events happen next that enable the β subunit and the IRS protein to bind together? A. Conformational changes in the β subunits occur as a result of insulin binding to the α subunit. These expose serine/threonine kinase active sites in the β subunits, which next phosphorylate IRS proteins on select threonine residues. Phosphothreonine binding sites (PTB domain) found in the β subunit of the receptor then bind to the P-threonine residues in the IRS protein. B. Conformational changes in the β subunits occur as a result of insulin binding to the α subunit. These expose the tyrosine kinase active sites in the β subunits, which next phosphorylate IRS proteins on select tyrosine residues. Phosphotyrosine binding sites (PTB domain) found in the β subunit of the receptor then bind to the P-tyrosine residues in the IRS protein. C. Binding of insulin induces conformational changes in the β subunits, which enable them to autophosphorylate on tyrosine residues. These P-tyrosine residues are recognized by the phosphotyrosine binding sites (PTB domain) present in an IRS protein. D. Binding of insulin induces conformational changes in the β subunits, which expose their serine/threonine kinase active sites, enabling them to autophosphorylate on threonine residues. These P-threonine residues are recognized by the Src homology 2 sites (SH2 domain) present in an IRS protein.

C. Binding of insulin induces conformational changes in the β subunits, which enable them to autophosphorylate on tyrosine residues. These P-tyrosine residues are recognized by the phosphotyrosine binding sites (PTB domain) present in an IRS protein.

Which of the following can enter glycolysis without additional reactions? A. Both products from lactose after lactate treatment B. Both products from sucrose after sucrase treatment C. Both products from maltose after maltase treatment D. Glycerol

C. Both products from maltose after maltase treatment

Which of the following enzyme regulatory mechanisms is not reversible? A. Phosphorylation of serine, threonine, or tyrosine residues. B. Binding of ATP or ADP to the regulatory site on phosphofructokinase-1. C. Conversion of pepsinogen to pepsin by aspartate-mediated cleavage. D. Binding of CTP to the regulatory site of aspartate transcarbamoylase (ACTase). E. cAMP-mediated dissociation of protein kinase A regulatory subunit from catalytic subunit.

C. Conversion of pepsinogen to pepsin by aspartate-mediated cleavage.

Beta-adrenergic receptor signaling must be terminated quickly or an extended metabolic shift could cause serious problems for the organism. Which best explains how receptors are "desensitized"? A. G protein-coupled receptor kinases (GRKs) lead to the activation of other protein kinases, which block ligand binding to the receptor binding pocket. B. G proteins will lead to activation of proteases, which reduces the overall amount of receptor on the cell membrane. C. G protein-coupled receptor kinases (GRKs) are protein kinases that phosphorylate receptors for internalization. D. Arrestin will first bind the receptor, allowing G protein-coupled receptor kinase to recognize the GPCR and phosphorylate the receptor. This increases the GTPase activity of the G protein.

C. G protein-coupled receptor kinases (GRKs) are protein kinases that phosphorylate receptors for internalization.

After inhalation of the asthma drug fluticasone, what two signaling mechanisms mediated by the glucocorticoid receptor (GR) lead to a decrease in airway inflammation and relief of asthma symptoms? A. GR activates NFkB induction of Cox2 gene expression and GR blocks expression of the annexin gene. B. GR blocks induction of GLUT1 gene expression and GR activates expression of the ibuprofen gene. C. GR blocks NFkB induction of Cox2 gene expression and GR activates expression of the annexin gene. D. GR stimulates NFkB gene expression and GR inhibits expression of the anti-histamine gene. E. None of these answers are correct.

C. GR blocks NFkB induction of Cox2 gene expression and GR activates expression of the annexin gene.

Which of the following is true regarding the roles of adenylylation and uridylylation in the control of glutamine synthetase? A. Adenylylation and deadenylylation processes of glutamine synthetase regulation use two different enzymes. B. Low levels of glutamine in the cell stimulate the deuridylylation activity of uridylyltransferase. C. High levels of ATP and α-ketoglutarate result in more deadenylylated glutamine synthetase. D. High uridylylation activity of uridylyltransferase increases the amount of adenylylated glutamine synthetase.

C. High levels of ATP and α-ketoglutarate result in more deadenylylated glutamine synthetase.

Caffeine leads to a vasoconstriction, raises the epinephrine levels, and increases nervous signaling. A metabolite of caffeine blocks phosphodiesterase. What is the most likely impact of caffeine on cell signaling? A. Caffeine directly binds and activates the protein kinases which signal the described effects, enhancing the effects of caffeine. B. The vascular effects of caffeine are long term, indicating a steroid-enhanced activity supported by loss of phosphodiesterase action. C. Inhibition of the phosphodiesterase results in an elevated cAMP levels and PKA activation, leading to increased glycogen breakdown and increased phosphorylation of events controlling the physiology of caffeine addiction. D. Phosphodiesterase leads to increased PIP2 breakdown, inhibiting Akt signaling. This alters the glycogen metabolism and glucose uptake in the liver after caffeine ingestion.

C. Inhibition of the phosphodiesterase results in an elevated cAMP levels and PKA activation, leading to increased glycogen breakdown and increased phosphorylation of events controlling the physiology of caffeine addiction.

Regulation of metabolic flux is dependent on two primary factors, one of them is availability of substrates, what is the other primary factor? A. Value for the change in standard free energy under physiological conditions, it can be high or low. B. Enzyme localization as exemplified by tissue expression, subcellular location, and membrane insertion. C. Level of enzyme activity as exemplified by tissue localization, allosteric control, and protein synthesis. D. Degree of substrate reactivity exemplified by the level of phosphorylation and number of C=C bonds. E. If the valve is completely open then the flux is high, however if the valve is half-way closed, then 50%.

C. Level of enzyme activity as exemplified by tissue localization, allosteric control, and protein synthesis.

Phosphorylation of glucose requires 1 ATP. Can the reverse reaction be used for substrate-level phosphorylation? A. Yes, any reaction that involves ATP in either the forward or reverse direction is considered substrate-level phosphorylation. B. Yes, the breakdown of ATP in a metabolic reaction is always balanced with the synthesis of ATP in the reverse reaction. C. No, phosphate hydrolysis of glucose-6-phosphate is not spontaneous enough to couple to ATP synthesis. D. No, ATP is primarily produced through oxidative phosphorylation, and there is an insufficient amount of ADP available for substrate-level phosphorylation to occur.

C. No, phosphate hydrolysis of glucose-6-phosphate is not spontaneous enough to couple to ATP synthesis.

Which of the following is not a primary mechanism used to regulate the catalytic efficiency of enzymes? A. proteolytic processing B. binding of regulatory molecules C. RNA synthesis D. covalent modification

C. RNA synthesis

Which of the following is correct about the binding of epidermal growth factor to its receptor? A. Serine residues are the targets for phosphorylation. B. Epidermal growth factor binds to the dimer form of the receptor. C. The cytoplasmic tail of EGFR2 is phosphorylated before EGFR1. D. The amino-terminal tail of EGFR2 is phosphorylated before EGFR1.

C. The cytoplasmic tail of EGFR2 is phosphorylated before EGFR1.

The signaling pathways linking vision, smell, and taste to neuronal signaling have processes in common, but also have one distinct difference. Which statement below best describes that distinction. A. They each use a different type of receptor protein; GPCR, RTK and TNF classes of receptors. B. They each use GSa proteins as the upstream signal, but each GSa stimulates different target proteins. C. The second messenger in each of these signaling systems is distinct; GMP, cAMP, DAG/IP3 . D. The hormone that stimulates each of these pathways is distinct; insulin, glucagon, epinephrine. E. There are no distinctions between these pathways in that all three pathways activate glucose export.

C. The second messenger in each of these signaling systems is distinct; GMP, cAMP, DAG/IP3 .

Which of the following mutations would most impact PKA, leading to a constitutively active enzyme? A. a mutation in the cAMP binding domain of the regulatory subunit that blocks the ability of cAMP to bind to the protein B. a mutation of the catalytic subunit that allows cAMP to bind directly to the active site of the kinase C. a mutation in the catalytic subunit where the kinase can still bind its target but no longer binds the regulatory subunit D. a mutation in the regulatory pseudosubstrate (Arg-Arg-Gly-Ala-Ile) where Ala is mutated to an Ser

C. a mutation in the catalytic subunit where the kinase can still bind its target but no longer binds the regulatory subunit

If phosphofructokinase experienced a mutation that interfered with substrate binding, then what other enzyme is going to be most immediately impacted in terms of accessing substrate? A. fumarase B. hexokinase C. aldolase D. glucolactonase

C. aldolase

Lysophosphatidic acid (LPA) is a water-soluble phospholipid derivative found in blood serum, where it binds to receptors throughout the body, inducing cell growth and other effects. This is an example of what kind of signaling system? A. autocrine B. paracrine C. endocrine D. exocrine

C. endocrine

Cancer cells have many alterations in their metabolic pathways, including some that alter the way they metabolize and use glucose. This is known as the Warburg effect. One component of the Warburg effect is the inhibition of the enzyme that converts pyruvate to acetyl CoA. Under these conditions, what metabolite will be elevated in cancer cells as compared to noncancerous cells even under normal oxygen saturation? A. NADH B. pyruvate C. lactate D. CO2

C. lactate

Kinase enzymes phosphorylate other proteins and enzymes. This is a common mechanism of covalently modifying enzymes in order to control their catalytic efficiency. Which of the following amino acids is not targeted for phosphorylation by kinases? A. serine B. tyrosine C. leucine D. threonine

C. leucine

Which enzyme is responsible for terminating the activity of membrane-bound PIP3? A. Akt protein B. phosphatidylinositide-3 kinase, PI-3K C. phosphatase and tensin homolog, PTEN D. phosphoinositide-dependent kinase, PDK1

C. phosphatase and tensin homolog, PTEN

Individuals with a deficiency in the aldolase B enzyme have a condition known as hereditary fructose intolerance. The metabolic intermediate that accumulates in the liver as a result of this deficiency can have an indirect, activating effect on hepatic glucokinase. The blood glucose levels in these individuals A. would be lower than normal due to the increased concentration of glucokinase. B. would be higher than normal due to the increased reaction rate of glucokinase. C. would be lower than normal due to the increased reaction rate of glucokinase. D. would be higher than normal due to the increased concentration of glucokinase.

C. would be lower than normal due to the increased reaction rate of glucokinase.

What is Inositol triphosphate target protein? 1. Calcium channel protein 2. Protein kinase G 3. Protein kinase A 4. Calmodulin 5. Protein kinase C

Calcium channel protein

Glucokinase is important for the regulation of glycolysis because it A. has a high affinity for glucose. B. is inhibited by glucose-6-phosphate. C. inhibits insulin release in pancreatic cells in response to high glucose. D. traps extra glucose in liver cells for glycogen production.

D. traps extra glucose in liver cells for glycogen production.

Which of the following best describes the relationship among a subunit of the protein, metal cofactors, and ligands? A. Metal ions interact with one another within the protein at a distant location from the ligand interaction. B. Metal ions and ligands interact with the protein in locations that are all quite distant from one another. C. Ligands interact with one another proximally within the protein at a distant location from the metal ion interaction. D. A metal ion and ligand interact with the protein in locations proximal to one another.

D. A metal ion and ligand interact with the protein in locations proximal to one another.

Signaling activity of G proteins is controlled by GTPase activating proteins (GAPs) and Guanine exchange factors (GEFs). What are the mechanisms by which GAPs and GEFs control G proteins (GPs)? A. GAPs inhibit GPs by stimulating GDP-GTP exchange; GEFs activate GPs by stimulating GTP hydrolysis. B. GAPs stimulate GPs by blocking GTP hydrolysis; GEFs inhibit GPs by stimulating GTP-GDP exchange. C. GEFs inhibit GPs by stimulating GTP hydrolysis; GAPs activate GPs by stimulating GDP-GTP exchange. D. GAPs inhibit GPs by stimulating GTP hydrolysis; GEFs activate GPs by stimulating GDP-GTP exchange. E. None of these answers are correct.

D. GAPs inhibit GPs by stimulating GTP hydrolysis; GEFs activate GPs by stimulating GDP-GTP exchange.

You have a mystery hormone (agonist), and to test the nature of the agonist you add it to a dish of cultured liver cells. Shortly afterward you observe an increase in protein kinase activity. In a second experiment, you find the kinase is inhibited if you add an adenylate cyclase inhibitor to the cells prior to adding your mystery agonist. Which kind of receptor system is the agonist signaling through? A. steroid hormone receptor B. ion channel C. protein tyrosine kinase receptor D. GPCR

D. GPCR

Glucagon binding to the glucagon receptor inhibits which of the following processes? A. cAMP synthesis B. Glycogen degradation C. Glucose synthesis D. Glycogen synthesis

D. Glycogen synthesis

Why is HFCS preferred over corn syrup for sweetening beverages and processed foods? A. HFCS is more natural than corn syrup. B. HFCS is less caloric than corn syrup. C. HFCS is less costly to produce than corn syrup. D. HFCS is sweeter than corn syrup.

D. HFCS is sweeter than corn syrup.

In which situation is glycolysis alone likely to be a major contributor to ATP generation? A. In liver cells B. Under aerobic conditions C. In muscle cells D. In erythrocytes

D. In erythrocytes

Name the enzymes that catalyze the two substrate level phosphorylation reactions in glycolysis. A. Hexokinase/phosphofructokinase-1 B. Phosphoglycerate kinase/phosphofructokinase-1 C. Glucokinase/pyruvate kinase D. Pyruvate kinase/phosphoglycerate kinase E. None of these answers are correct.

D. Pyruvate kinase/phosphoglycerate kinase

You are culturing mammalian brain cells with standard growth media that includes 10% fetal bovine serum (FBS). FBS has a number of hormones and other components that stimulate cell growth. Over a busy weekend you made a mistake and left the cells in media without FBS. These cells have begun apoptosis while normally cultured cells are growing and surviving just fine. Which might be the reason for the dying cells? A. Loss of positive growth factors such as TNF-alpha activates the NF kappa B pathway, activating crtical anti-apoptotic genes. B. Loss of activators in FBS allows the cells to begin to go into the Go phase, and the cell death is due to an overactive protein kinase A. C. FBS must have included a growth factor signaling to insulin. Loss of this leads to an increase in glucose input into the cells. D. Withdrawal of a positive growth signal induced the cell death pathway of TNF-alpha.

D. Withdrawal of a positive growth signal induced the cell death pathway of TNF-alpha.

Infants express the enzyme lactase in their intestines to metabolize lactose. How many net moles of ATP can be generated from 2 moles of lactose under anaerobic conditions by infants with high levels of lactase? A. 2 net ATP B. 4 net ATP C. 6 net ATP D. 32 net ATP E. 8 net ATP

E. 8 net ATP

Why do mutations in Ras that block its intrinsic GTPase activity result in cancer cell division even in the absence of epidermal growth factor (EGF) signaling? A. Because Ras mutations that block GTPase activity bind EGF with high affinity and it does not dissociate. B. Because Ras mutations that block GTPase activity result in an occasionally activated Ras-GDP. C. Because Ras mutations that block GTPase activity result in a constitutively inhibited Ras-GTP. D. Because Ras mutations that block GTPase activity result in a constitutionally activated Ras-GDP. E. Because Ras mutations that block GTPase activity result in a constitutively activated Ras-GTP.

E. Because Ras mutations that block GTPase activity result in a constitutively activated Ras-GTP.

Why does it make sense that dreaming about cake and almost stepping on a snake both stimulate the same downstream biochemical response? A. Because if you are scared or hungry, you need less glucose. B. Because if the snake is hungry, you don't want to eat a piece of cake. C. Because if you are hungry you want to eat a piece of cake. D. Because if you are angry you want to step on a snake. E. Because if you are scared or hungry, you need more glucose.

E. Because if you are scared or hungry, you need more glucose.

Which of the following metabolic conversions is considered a reversible isomerase reaction? A. Fructose-6-phosphate + ATP à Fructose-1,6-bisphosphate + ADP B. Phosphoenolpyruvate + ADP à Pyruvate + ATP C. Glucose + ATP à Glucose-6-phosphate + ADP D. Fructose-1,6-bisphosphate à Dihydroxyacetone phosphate + Glyceraldehyde-3-phosphate E. Glucose-6-phosphate à Fructose-6-phosphate

E. Glucose-6-phosphate à Fructose-6-phosphate

The signaling pathways linking vision, smell, and taste to neuronal signaling have processes in common, but also have one distinct difference. Which statement below best describes that distinction. A. The hormone that stimulates each of these pathways is distinct; insulin, glucagon, epinephrine. B. They each use GSa proteins as the upstream signal, but each GSa stimulates different target proteins. C. There are no distinctions between these pathways in that all three pathways activate glucose export. D. They each use a different type of receptor protein; GPCR, RTK and TNF classes of receptors. E. None of these answers are correct

E. None of these answers are correct

What explains the observation that glucocorticoids only regulate genes involved in carbohydrate metabolism in liver cells and inflammation in immune cells given that all cells have glucocorticoid receptors? A. Cell-specific production of steroid noncompetitive inhibitors. B. Cell-specific enzymes that degrade glucocorticoids. C. Cell-specific expression of DNA recombination enzymes. D. Cell-specific expression of glucocorticoid synthesizing enzymes. E. None of these answers are correct.

E. None of these answers are correct.

Which glycolytic enzyme is responsible for decreased flux through glycolysis when citrate levels are high and AMP levels are low? A. Pyruvate kinase B. Glyceraldehyde-3P dehydrogenase C. Hexokinase D. Enolase E. Phosphofructokinase I

E. Phosphofructokinase I

What is Cyclic AMP target protein? 1. Calcium channel protein 2. Protein kinase G 3. Protein kinase A 4. Calmodulin 5. Protein kinase C

Protein kinase A

What is Diacylglycerol target protein? 1. Calcium channel protein 2. Protein kinase G 3. Protein kinase A 4. Calmodulin 5. Protein kinase C

Protein kinase C

Following protein kinase A activation in a liver cell in response to epinephrine binding to the b2 adrenergic receptor, which of the following processes will occur? a. Glucose synthesis will be turned on. b. Glycogen degradation will be turned on. c. Glucose synthesis will be turned off. d. Glycogen synthesis will be turned off. e. GLUT1 expression will be up-regulated. f. DAG stimulation of PKC kinase activity

a. Glucose synthesis will be turned on. b. Glycogen degradation will be turned on. d. Glycogen synthesis will be turned off.

Which of the following are characteristics of allosteric enzymes such as aspartate transcarbamoylase. a. Often have a sigmoidal (S-shaped) curve of Vo versus [S]. b. Conform to Michaelis-Menten kinetics. c. Are usually small single subunit proteins. d. Undergo conformational changes between the R and T state. e. Most all allosteric enzymes contain an iron heme group. f. The binding site for effectors is inside the active site. g. Can have a regulatory subunit and catalytic subunit.

a. Often have a sigmoidal (S-shaped) curve of Vo versus [S]. d. Undergo conformational changes between the R and T state. g. Can have a regulatory subunit and catalytic subunit.

Which of the following processes are points of regulation for controlling enzyme-mediated biochemical reactions. a. Proteolytic Processing b. Guanine Methylation c. Protein Targeting d. Incorporation of D Amino Acids e. Carboxyl Termini Dehydration f. RNA Processing g. Protein Degradation h. Dihydrolipidation of Arginine i. Disulfide Bond Acetylation j. Serine Phosphorylation

a. Proteolytic Processing c. Protein Targeting f. RNA Processing g. Protein Degradation j. Serine Phosphorylation

Tasting involves cell-signaling processes generating nerve signals transduced by membrane depolarization. Sweet tastes result in PIP2 hydrolysis, while salty tastes stimulate Na+ ion transport leading to membrane potential. Which answers below best describe signaling mechanisms for sweet and salty? a. Salty stimulates Na+ ion transport into cells, indicating ion channels are involved. b. Sweet ligands bind to and close sodium channels, which initiates a membrane potential. c. Sweet and salty signaling pathways use the same taste receptor tyrosine kinase. d. Sweet utilizes the GPCR signaling pathway leading to phospholipase C activation. e. Sweet signaling and salty signaling pathways use distinct taste receptor proteins. f. Salty signaling uses nuclear receptor pathway and sweet signaling uses TNF signaling

a. Salty stimulates Na+ ion transport into cells, indicating ion channels are involved. d. Sweet utilizes the GPCR signaling pathway leading to phospholipase C activation. e. Sweet signaling and salty signaling pathways use distinct taste receptor proteins.

Example of covalent modification in glutamine synthetase activity

adenylation uridylylation

When compared to the R state, the T state of aspartate transcarbamoylase a. has greater separation of the catalytic subunits b. is bound to CTP c. is less catalytically active d. is bound to aspartate e. is bound to ATP f. is more catalytically active g. has less separation of the catalytic subunits

b. is bound to CTP c. is less catalytically active g. has less separation of the catalytic subunits

Example of allosteric control in glutamine synthetase activity

binding of ATP binding of glutamine binding of Pi

Place the following steps in the correct order for the EGF receptor signaling pathway a. A GEF protein binds to the SH3 domains of GRB2. b. Cytoplasmic tails of EFG receptors are phosphorylated. c. Raf kinase binds to Ras-GTP and is phosphorylated by Src d. GRB2 binds to a phosphotyrosine on the EGF receptor. e. Ras-GDP binds to GEF protein stimulating GDP-GTP exchange. f. Binding of EGF to EGF receptors stimulates dimerization.

f. Binding of EGF to EGF receptors stimulates dimerization. b. Cytoplasmic tails of EFG receptors are phosphorylated. d. GRB2 binds to a phosphotyrosine on the EGF receptor. a. A GEF protein binds to the SH3 domains of GRB2. e. Ras-GDP binds to GEF protein stimulating GDP-GTP exchange. c. Raf kinase binds to Ras-GTP and is phosphorylated by Src