The primary role of the pentose phosphate pathway is to produce:

e) NADPH and Ribose 5-phosphate and erythrose 4-phosphate

a) ATP and Fructose 6-phosphate.

c) Sedoheptulose 7-phosphate and Ribulose 1-phosphate.

d) NADP+ and Ribose 5-phosphate.

What is the role of glucose 6-phosphatase during glycogen breakdown?

c) Leads to the release of glucose from the liver to enter the bloodstream.

a) Allows free glucose to exit muscles and enter the bloodstream.

b) Blocks glucose 6-phosphate from exiting the liver.

d) Makes glucose enter the pentose phosphate pathway.

e) Permits glucose 6-phosphate to enter glycogen synthesis in the liver.

Why does the liver need glucagon and epinephrine in activation of glycogen breakdown?

a) Epinephrine is needed to bind alpha-adrenergic receptors to activate the phosphoinositide pathway to release Ca²⁺ from the endoplasmic reticulum.

b) Epinephrine is needed to bind beta-adrenergic receptors to activate the phosphoinositide pathway to release Ca²⁺ from the endoplasmic reticulum.

c) Glucagon is needed to bind beta-adrenergic receptors to activate protein kinase C.

d) Glucagon can only activate phospholipase C.

e) Epinephrine is needed to directly bind adenylate cyclase.

What is the effect of “Limit dextrin”?

a) A physical barrier that blocks Glycogen phosphorylase from reaching alpha-1,6 branch points.

b) The number of dextrins that amylase can cleave at once.

c) Helps Glycogen phosphorylase find alpha-1,6 branch points.

d) Inhibits protein kinase A phosphorylation of phosphorylase kinase.

e) Recruits glycogen synthase to the site of glycogen extension.

In Von Gierke Disease the glucose 6-phosphatase enzyme is defective. Which of the following is TRUE?

c) Glucose 6-P accumulates in the endoplasmic reticulum of liver cells and prevents glucose from entering the bloodstream.

a) Glucose 6-P accumulates in the endoplasmic reticulum of muscle cells and prevents glucose from being used as an energy source.

b) Glucose 6-P accumulates in the endoplasmic reticulum of muscle cells and prevents glucose from entering the bloodstream.

d) Glucose 6-P accumulates in the endoplasmic reticulum of muscle cells and prevents glucose from being incorporated into glycogen.

e) Glucose accumulates in the endoplasmic reticulum of brain cells and prevents its use as an energy source.

Which statement is INCORRECT about Insulin?

d) Insulin receptors in target tissues act through cAMP to promote protein phosphorylation.

a) Insulin is a polypeptide hormone consisting of two disulfide-linked chains.

b) Insulin is secreted by beta-cells of pancreatic islets in response to high blood glucose and amino acid levels.

c) Insulin promotes synthesis of glycogen, triacylglycerols, and proteins.

e) One of the actions of insulin is to increase the number of glucose transporters on the surface of adipose and muscle cells.

What characteristics are found in glycogen and its synthesis/breakdown?

a) The primary linkages between glucose molecules are α-1,4 glycosidic bonds.

b) Branch points in glycogen are α-1,6 glycosidic bonds.

c) Glycogen breakdown releases Glucose-1-phosphate.

d) Released Glucose-1-phosphate is converted to Glucose-6-phosphate through phosphoglucomutase activity.

Which is the INCORRECT statement about the regulation of glycogen synthesis and degradation?

d) Phosphorylated glycogen synthase is active.

a) Glucose 6-phosphate allosterically activates glycogen synthase.

b) ATP allosterically inhibits glycogen phosphorylase.

c) Glucagon leads to the phosphorylation of both glycogen synthase and glycogen phosphorylase.

e) Protein phosphatase 1 can deactivate glycogen phosphorylase by removing phosphate groups.

Consider the following step in Phosphoglucose isomerization: What is the direct role of the glutamate?a) Donates proton to Carbon 1 to close the sugar ring. b) Donates proton to Carbon 2 to produce enol intermediate. c) Deprotonates Carbon 2 hydroxyl to produce an enol intermediate. d) Takes/abstracts proton from Carbon 2 to produce an enol intermediate. e) Abstracts proton from Carbon 2 to close the sugar ring.

d) Takes/abstracts proton from Carbon 2 to produce an enol intermediate.

a) Donates proton to Carbon 1 to close the sugar ring.

b) Donates proton to Carbon 2 to produce enol intermediate.

c) Deprotonates Carbon 2 hydroxyl to produce an enol intermediate.

e) Abstracts proton from Carbon 2 to close the sugar ring.

In the first step of glycolysis, hexokinase phosphorylates Glucose to make Glucose-6-phosphate. How does the phosphate get transferred to Glucose?

b) The C6-OH is deprotonated by the enzyme to create the C6-O⁻ nucleophile that attacks the gamma phosphate of ATP to make Glucose 6-phosphate.

a) Free orthophosphate diffuses into the active enzyme pocket to attack the hydroxyl on carbon 6 (C6-OH) to make Glucose 6-phosphate.

c) An activated water cleaves the gamma phosphate from ATP then the orthophosphate attacks the C6-OH to make Glucose 6-phosphate.

d) The C6-OH is deprotonated by the enzyme to create the C6-O⁻ electrophile that attacks the gamma phosphate of ATP to make Glucose 6-phosphate.

e) The Mg²⁺ held by the enzyme cleaves the gamma phosphate after which the orthophosphate attacks the C6-OH to make Glucose 6-phosphate.

ATP is formed in the glycolytic pathway:

b) From phosphoenolpyruvate and from 1,3-bisphosphoglycerate.

a) By the action of pyruvate dehydrogenase which also leads to the formation of acetyl CoA.

c) From NADH by the process of substrate level phosphorylation.

d) From fructose 1,6-bisphosphate and from glucose 6-phosphate.

e) Using the energy present in the thioester bond of acetyl CoA.

What happens to phosphofructokinase (PFK1) activity in the presence of Fructose 2,6-bisphosphate (F2,6BP)?

c) F2,6BP decreases the inhibitory effect of ATP on PFK1.

a) F2,6BP decreases the affinity of PFK1 for Fructose 6-phosphate.

b) F2,6BP increases the cooperativity of PFK1.

d) F2,6BP increases the inhibitory effect of ATP on PFK1.

In glycolysis the aldolase step converts one Fructose 1,6-bisphosphate to the following product(s):

c) 1 Glyceraldehyde 3-phosphate and 1 Dihydroxyacetone phosphate

a) 2 Glyceraldehyde 3-phosphate

b) 2 Dihydroxyacetone phosphate

d) 1 Dihydroxyacetone phosphate and 1 Enediolate

How can the inhibition of phosphofructokinase (PFK1) by ATP lead to the inhibition of hexokinase?

a) Inhibition of PFK1 results in more Fructose 6-phosphate, which isomerizes with Glucose 6-phosphate. Hexokinase is inhibited by elevated Glucose 6-phosphate.

b) Inhibition of PFK1 results in more Fructose 1,6-bisphosphate, which directly inhibits Hexokinase.

c) Inactive PFK1 binds to Hexokinase to prevent Glucose 6-phosphate production.

d) Inactive PFK1 leads to the buildup of glycogen, which inhibits Hexokinase function.

Why is ATP a good phosphate donor?

a) The gamma-phosphate has a -1 charge.

b) ATP is less hydrated than ADP.

c) Charge repulsion between gamma and beta phosphate.

In a “classic” ATPase enzyme pocket the gamma phosphate of ATP is directly released due to:

b) Nucleophilic attack by activated water (deprotonated water).

a) Depolarization by magnesium.

c) Polarization by an Arginine finger.

A Thioester bond is favored over an ester bond for nucleophilic attack due to which of the following?

a) The lack of resonance between the carbonyl oxygen and the sulfur atom.

b) The facile protonation of the sulfur atom.

c) Sulfur is smaller than oxygen.

d) The strong resonance between the ketone oxygen and the sulfur atom.

e) The nucleophilic potential of the sulfur atom.

The full oxidation of FADH₂ results in which of the following?

b) Loss of 2 electrons and 2 protons.

d) Gain of 2 electrons and 2 protons.

e) Gain of 2 electrons and 1 proton.

The Walker Box residues in the ATP binding pocket of an ATPase organize a Mg²⁺. What is the direct effect of Mg²⁺?

c) Neutralizes phosphate negative charges.

a) Nucleophilic attack of the gamma phosphate.

b) Organize a water to make it the electrophile.

d) Polarizes the alpha phosphate.

What is the effect of mutating the Arg finger to an Asp in the ATP binding pocket of an ATPase?

a) The negative charge of the Asp repels the negative charge of the gamma phosphate.

b) The Asp acts as a nucleophile instead of a water.

c) The positive charge of the Asp enhances the polarization of the gamma phosphate.

d) The negative charge of the Asp binds to Ca²⁺.

e) Polarizes the alpha phosphate.

NADH is a hydride carrier. Upon its oxidation, NADH will:

c) Lose 2 electrons and 1 proton.

a) Gain 1 electron and 1 proton.

b) Lose 1 electron and 2 protons.

d) Gain 2 electrons and 2 protons.

e) Lose 1 electron and gain 1 proton.

What feature is shared by the Tyrosine Kinase Receptor Complexes discussed in class?

c) Conformational changes occur upon ligand binding.

a) Transautophosphatase activity.

b) Dephosphorylation of ligand.

How does heterotrimeric G-protein (HGP) activation lead to calcium release from the endoplasmic reticulum (ER)?

a) GTP-bound HGP activates phospholipase C (PLC) which cleaves phosphoinositide 4,5-bisphosphate (PIP₂) to release IP₃. IP₃ binds to its receptor on the ER leading to calcium release.

b) GDP-bound HGP activates phospholipase C (PLC) which cleaves PIP₂ to release IP₃. IP₃ binds to its receptor on the ER leading to calcium release.

c) GTP-bound HGP activates phospholipase D (PLD) which cleaves PIP₃ to release IP₃. IP₃ binds to its receptor on the ER leading to calcium release.

d) GTP-bound HGP activates phospholipase C (PLC) which cleaves PIP₂ to release diacylglycerol (DAG) into the cytoplasm. DAG binds to its receptor on the ER leading to calcium release.

e) GTP-bound HGP activates phospholipase A (PLA) which cleaves PIP₂ to release IP₃. IP₃ binds to its receptor on the ER leading to calcium release.

Which of the following is NOT an intracellular mediator (second messenger) of hormone action?

e) All of the above are intracellular mediators.

d) Inositol trisphosphate (IP₃)

Which of the following does NOT affect membrane fluidity?

b) The charge on the hydrophilic head group

e) Double bonds in the lipid hydrocarbons

Which of the following statements about membrane transport is TRUE?

d) Solutes that cross a cell membrane by facilitated or passive diffusion will move down a concentration gradient.

a) Membrane transport proteins make many strong, covalent interactions with their polar substrates, and these replace solute-water interactions.

b) There is no energy barrier to the transport of charged or polar solutes across a cell membrane.

c) If a solute crosses a cell membrane by facilitated diffusion or active transport, the transport process can never be saturated.

e) If a solute crosses a cell membrane through an active transport it will move across the bilayer until the concentration gradient reaches an equilibrium.

Which of the following statements about integral membrane proteins is FALSE?

c) They can be released from membranes by treatments that break hydrogen bonds or interfere with electrostatic interactions.

a) They sometimes consist of beta-sheets that curl up to form a hollow cylinder that serves as a pore in the membrane.

b) Membrane proteins with one or more transmembrane alpha helix/helices may have functional domains on both sides of the membrane.

e) Formation of membrane-spanning alpha helices is favored when the amino acid chain is surrounded by membrane fatty acyl chains, and there are no water molecules with which peptide groups can form hydrogen bonds.

The binding energy of an Enzyme–Substrate interaction is the sum of which of the following?

e) Weak bonds such as ionic, hydrogen and hydrophobic interactions.

a) Strong bonds such as H-bonds, hydrophobic and ionic interactions.

b) Strong covalent bonds such as disulfide bonds.

d) Electrostatic van der Waals interactions.

Which is TRUE about the effect of an enzyme on the activation of a reaction?

c) Lowers the transition state so less energy is required to complete the reaction.

a) Increases the transition state so less energy is required to complete the reaction.

b) Lowers the transition state so more energy is required to complete the reaction.

d) Increases the transition state so more energy is required to complete the reaction.

What property does a carbonyl have to make it a good target for a nucleophilic attack?

b) A dipole with a partial positive charge on the carbon and a partial negative charge on the oxygen.

a) A dipole with a partial positive charge on the oxygen and a partial negative charge on the carbon.

c) A quadrupole with a formal positive charge on the carbon.

d) The lack of resonance with the neighboring oxygen of an ester.

e) The resonance in a thioester bond.

Thioester is more reactive compared to an ester bond due to which of the following?

a) The lack of resonance between the carbonyl oxygen and the sulfur atom

b) The facile protonation of the sulfur atom

c) Pantothenic acid is a good leaving group

d) The strong resonance between the ketone oxygen and the sulfur atom

e) The nucleophilic potential of the sulfur atom

The full reduction of FAD results in which of the following?

d) Gain of 2 electrons and 2 protons

b) Loss of 2 electrons and 2 protons

e) Gain of 2 electrons and 1 proton

Aspirin is an irreversible inhibitor. How does it inhibit COX?

a) Aspirin reacts with a serine in the catalytic pocket of COX to form a covalent bond and inhibit enzyme activity

b) Aspirin electrostatically interacts with the key serine in COX to block activity

c) Aspirin accumulates in the hydrophobic binding pocket of COX to block substrate access

d) Aspirin mimics the natural substrate and competes for binding COX

e) Aspirin binds the COX substrate to inhibit activity

Which of the following is a second messenger of hormone action?

d) Inositol trisphosphate (IP3)

What does oxidative catabolism ultimately produce?

a) Reduced NADH + H⁺, FADH₂, and ATP

b) ATP and oxidized NADH + H⁺

In a “classic” ATPase enzyme pocket, the gamma phosphate of ATP is directly released due to:

b) Nucleophilic attack by activated (deprotonated) water

c) Repulsion by an Arginine finger

Pyruvate kinase (PK) is regulated in the liver and other tissues. Which of the following is FALSE?

a) ATP allosterically activates PK in the liver

b) PK is phosphorylated by PKA in the liver

c) PK is inactivated by ATP in muscle

d) F1,6BP feeds forward to activate PK in muscle

e) Acetyl-CoA feeds back to inhibit PK in muscle

MCB 450 Exam 3 Practice Question

Authored by Dhriti Patel

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MULTIPLE CHOICE QUESTION

30 sec • 1 pt

What is TRUE about Hereditary Fructose Intolerance?

a) ATP levels fall.

b) Uric acid crystals form.

c) Fructose 1-phosphate accumulates.

d) Production of glyceraldehyde is blocked.

e) All of the above are TRUE.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Glucose-6-phosphate dehydrogenase (G6PD) deficiency in mature erythrocytes can lead to hemolytic anemia. The reason for cellular lysis of erythrocytes in this situation is due to the:

a) Increased rate of glycolysis in the erythrocytes.

b) Decrease in the NADPH levels which slows down all reductive biosynthetic pathways in the erythrocytes.

c) Increased levels of NADPH leading to low levels of oxidized glutathione as an antioxidant to protect red cells from oxidative damage.

d) Increased levels of NADP+ leading to low levels of reduced glutathione, leading to the production of Heinz bodies and membrane damage.

e) Reduced ability to synthesize ribose-5-phosphate through the oxidative phase of the hexose monophosphate shunt.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

In the pentose phosphate pathway, what normally inhibits Glucose 6-phosphate dehydrogenase?

a) Elevated Glucose 6-phosphate

b) Elevated NADH

c) Elevated NADPH

d) Elevated NADP+

e) Elevated NAD+

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

NADPH is used to kill microorganisms that are phagocytosed by white blood cells such as macrophages and neutrophils. Which of the following is/are NOT true?

a) NADPH is used to reduce oxidized glutathione, which is used in the conversion of H₂O₂ to water by glutathione peroxidase.

b) NADPH oxidase converts O₂ to superoxide as part of the respiratory burst.

c) NADPH is used by iNOS to generate NO as part of the respiratory burst.

d) The NADPH-dependent respiratory burst leads to the formation of HOCl and hydroxyl radicals that cause cellular damage to the microorganism.

e) B and C

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

Cells can use different pathways to meet certain needs. Which combination of pathways are used when more NADPH is needed than ribose 5-phosphate?

a) Glycolysis and the reverse non-oxidative part of the PPP

b) The oxidative and non-oxidative parts of the PPP in addition to gluconeogenesis

c) The oxidative portion of the PPP and glycolysis

d) The non-oxidative form of the PPP and glycolysis

e) The reverse non-oxidative part of the PPP and gluconeogenesis

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

In the phosphopentose isomerase reaction of the pentose phosphate pathway, Ribulose 5-phosphate is converted to Ribose 5-phosphate. What happens to the carbonyl?

a) The carbonyl is moved from the carbon-1 position of Ribulose to carbon-2 of Ribose 5-P.

b) The carbonyl is moved from the carbon-2 position of Ribulose to carbon-1 of Ribose 5-P.

c) The hydroxyl is moved from the carbon-2 position of Ribulose to carbon-1 of Ribose 5-P.

d) The hydroxyl is moved from the carbon-1 position of Ribulose to the carbon-2 of Ribose.

e) None of the above.

MULTIPLE CHOICE QUESTION

30 sec • 1 pt

In the galactose isomerization reaction, what would happen if the 4-ketose intermediate could not rotate?

a) The NAD⁺ would oxidize the C6–OH.

b) The NADH would return the hydride to the carbon 4 carbonyl and remake galactose.

c) The C4-ketone would be reduced to make glucose.

d) The NADH would rotate around the galactose instead to make glucose.

e) Galactose would react with glucose to reform lactose.

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MCB 450 Exam 3 Practice Question

What is TRUE about Hereditary Fructose Intolerance?

Glucose-6-phosphate dehydrogenase (G6PD) deficiency in mature erythrocytes can lead to hemolytic anemia. The reason for cellular lysis of erythrocytes in this situation is due to the:

In the pentose phosphate pathway, what normally inhibits Glucose 6-phosphate dehydrogenase?

NADPH is used to kill microorganisms that are phagocytosed by white blood cells such as macrophages and neutrophils. Which of the following is/are NOT true?

Cells can use different pathways to meet certain needs. Which combination of pathways are used when more NADPH is needed than ribose 5-phosphate?

In the phosphopentose isomerase reaction of the pentose phosphate pathway, Ribulose 5-phosphate is converted to Ribose 5-phosphate. What happens to the carbonyl?

In the galactose isomerization reaction, what would happen if the 4-ketose intermediate could not rotate?

The primary role of the pentose phosphate pathway is to produce:

What is the role of glucose 6-phosphatase during glycogen breakdown?

Which kinase inactivates glycogen synthase during glycogen breakdown?

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