Biochem Exam 4 Practice Questions

A diabetic patient accidentally injects 10x the normal insulin dose. Within 30 minutes, blood glucose drops to 2.5 mM (normal: 5 mM). Liver cells respond by attempting to increase glucose production, but muscle cells show a different response.

In the muscle cells of this patient, which regulatory change would occur at the PFK-2/FBPase-2 enzyme?

A) Protein kinase A phosphorylates the enzyme, activating FBPase-2 activity

B) Insulin-activated phosphatase dephosphorylates the enzyme, maintaining PFK-2 activity despite low glucose

C) High AMP levels override hormonal signals, activating PFK-2 regardless of phosphorylation state

D) Glucagon signaling phosphrylates the enzyme, activating FBPase-2 to slow glycolysis

E) The enzyme becomes insensitive to regulation due to sever hypoglycemia

B

What is the primary role of the mitochondria in relation to glycolysis

A) Mitrochondria adirectly catalyze the glycolysis reactions in the cytoplasm

B) Mitochondria provide the intial ATP supply needed to start the glycolysis pathway

C) Mitochondria produce the NAD+ required for the sixth enzyme reaction

D) Mitochondria convert pyruvate back into glycose to restart glycolysis

E) Mitochondria store glycose molecules until glycolysis is needed

B

After what step in glycolysis does the cell recoup its energy investment

A) when six-carbon sugar is split into two three-carbon sugars

B) during the isomerization of dihydroxyacetone

C) When the second phosphate is added to the glyceraldehyde 3-phosphate

D) when phosphate is transferred from 1,3- bisphosphoglycerate to ADP

E) after the dehydration reaction increase potential energy

D

which of the following correctly describes the fate of dihydroxyacetone phosphate (DHAP) produced in step 4?

A) DHAP is immediately converted to pyruvate without further processing

B) DHAP must be isomerized to glyceraldehyde 3- phosphate before continuing through glycolysis

C) DHAP exists glycolysis and enter the pentose phosphate pathway

D) DHAP is phosphorylated by ATP to form 1,3- bisphosphoglycerate

E) DHAP combines wit the other three carbon sugar to reform fructose 1,6 bisphosphate

B

the sixth enzyme reaction, what two improtant events occur simultaneously

A) ATp is consumed and glucose is phosphorylated

B) The six-carbon sugar is split and ATP is generated

C) A second phosphate is added to glyceraldehyde 3- phosphate and NAD+ is reduced to NADH

D) Phosphate is rearranged from the end to the middle of the molecules and water is removed

E) Pyruvate is formed and ATP is producec

C

A man collapses while running a marathon and is taken to the emergency room. His blood is found to be somewhat acidic, and further tests show increased lactate dehydrogenase activity. This enzyme is involved in which of the following pathways?

A) Anaerobic glycolysis

B) Beta-oxidation of fatty acids

C) Citric acid cycle

D) Pentose phosphate pathway

E) Glycogenolysis

A

Question 7

During an experiment, researchers add sodium arsenate (AsO4³⁻) to cells undergoing glycolysis. They observe that glucose consumption increases dramatically, but ATP production drops to near zero. NADH production continues normally.

Which step in glycolysis is most directly affected by arsenate, and what is the mechanism?

A) Step 3, (PFK-1): arsenate mimics phosphate and creates an unstable intermediate

B) Step 6 (GAPDH): arsenate replaces phosphate. forming 1-arseno-3-phosphoglycerate that spontaneously hydrolyzes

C) Step 7, (phosphoglycerate kinase) arsenate inhbits the enzyme competitively

D) Step 10 (pyruvate kinase): arsenate prevents PEP from transferring its phosphate to ADP

E) Step 1 (Hexokinase): arsenate cases futile cycling of glycose phosphorylation

B

A biochemists measures the delta Gvalues of all glycolytic reactions in actively contracting muscle tissue. She find that three reactions have large negative delta G values (-33.9, -18.8 and -23.0 kj/mol) while most other are near equilibrium.

If a pharmaceutical company wanted to design a drug to slow glycolysis in cancer cells with minimal effect on normal cells, which strategy would be most effecting based on these thermodynamic data.

A) Inhibit triose phosphate isomerase, since is has a positive delta G degree, and is easily reversed

B) Targed one of the three irreversible steps, but design the inhibitor to be selective for cancer specific isoforms

C) Target one of the three irreversible steps, but design the inhibitor to be selective for cancer specific isoforms.

D) Block all near equilibrium reaction simultaneously to prevent flux through the pathway

E) Activate phosphofructokinase-1 to cause substrate depletion upstream

B

Which statements are true and which are false?

I. Triose phosphate isomerase is considered a "kinetically perfect" enzyme because its kcat/Km approaches the theoretical maximum limited only by diffusion.

II. The aldolase reaction has a large positive ΔG°' (+23.9 kJ/mol), making it the rate-limiting step of glycolysis.

III. Phosphoglycerate mutase requires 2,3-bisphosphoglycerate as a catalytic cofactor to phosphorylate the active site histidine residue.

A) 1 and 2 are true 3 is false

B) 1 and 3 are true 2 is false

C) 2 and 3 are true 1 is false

D) 1 is true 2 and 3 are false

E) All are true

B

Which statements are true and which are false?

I. In the fed state, insulin activates a phosphatase that dephosphorylates PFK-2/FBPase-2, resulting in increased fructose-2,6-bisphosphate production.

II. Glucokinase in pancreatic β-cells has a Km of approximately 10 mM, allowing it to function as a glucose sensor that responds proportionally to blood glucose changes.

III. Hexokinase isoforms I and II are strongly inhibited by their product glucose-6-phosphate, while glucokinase (hexokinase IV) is not.

A) 1 and 2 are true 3 is false

B) 1 and 3 are true 2 is false

C) 2 and 3 are true 1 is false

D) 1 is true, 2 and 3 are false

E) All are true

E

Which statements are true and which are false?

I. The conversion of phosphoenolpyruvate to pyruvate by pyruvate kinase has a ΔG°' of -31.7 kJ/mol, making it essentially irreversible under cellular conditions.

II. Substrate-level phosphorylation occurs at two steps in glycolysis: the phosphoglycerate kinase reaction and the pyruvate kinase reaction.

III. The enolase reaction increases the phosphoryl transfer potential of its substrate by removing water and creating a high-energy enol phosphate bond.

A) 1 and 2 are true 3 is false

B) 1 and 3 are true 2 is false

C) 2 and 3 are true 1 is false

D) 1 is true, 2 and 3 are false

E) All are true

E

Which statements are true and which are false?

I. Phosphofructokinase-1 exhibits sigmoidal kinetics with respect to fructose-6-phosphate when ATP levels are high, indicating cooperative binding.

II. Citrate inhibits phosphofructokinase-1, signaling that the cell has sufficient biosynthetic precursors and energy from the TCA cycle.

III. The liver isoform of pyruvate kinase (PK-L) is activated by glucagon-stimulated phosphorylation, increasing glycolytic flux during fasting.

A) 1 and 2 are true 3 is false

B) 1 and 3 are true 2 is false

C) 2 and 3 are true 1 is false

D) 1 is true, 2 and 3 are false

E) All are true

A

Which statements are true and which are false?

I. Class I aldolase (found in animals) uses a Schiff base mechanism with an active site lysine, while Class II aldolase uses Zn²⁺ as a cofactor.

II. The glyceraldehyde-3-phosphate dehydrogenase reaction couples oxidation of an aldehyde to reduction of NAD+ and addition of inorganic phosphate to form a high-energy acyl phosphate.

III. Cancer cells preferentially use glycolysis over oxidative phosphorylation primarily because glycolysis produces ATP more efficiently per glucose molecule.

A) 1 and 2 are true 3 is false

B) 1 and 3 are true 2 is false

C) 2 and 3 are true 1 is false

D) 1 is true, 2 and 3 are false

E) All are true

A

Which statements are true and which are false?

I. Glucose-6-phosphate cannot cross the plasma membrane due to its negative charge, effectively trapping glucose inside the cell after phosphorylation.

II. The net equation for glycolysis is: Glucose + 2 NAD+ + 2 ADP + 2 Pi → 2 Pyruvate + 2 NADH + 2 ATP + 2 H₂O + 2 H+

III. Under anaerobic conditions in muscle, lactate dehydrogenase oxidizes NADH to NAD+, allowing glycolysis to continue producing ATP.

A) 1 and 2 are true 3 is false

B) 1 and 3 are true 2 is false

C) 2 and 3 are true 1 is false

D) 1 is true, 2 and 3 are false

E) All are true

E

Which statements are true and which are false?

I. The phosphoglucose isomerase reaction converts glucose-6-phosphate to fructose-6-phosphate through an enediol intermediate, with a ΔG°' of +1.67 kJ/mol.

II. Fructose-6-phosphate is a branch point metabolite that can enter glycolysis, gluconeogenesis, the pentose phosphate pathway, or the hexosamine biosynthetic pathway.

III. The committed step of glycolysis is the hexokinase reaction because it irreversibly traps glucose in the cell.

A) 1 and 3 are true 2 is false

B) 2 and 3 are true 1 is false

C) 1 is true, 2 and 3 are false

D) 1 and 2 are true: 3 is false

E) All are true

D

Which statements are true and which are false?

I. In erythrocytes, the steady-state concentration of 2,3-bisphosphoglycerate (4.0 mM) is much higher than that of 1,3-bisphosphoglycerate (0.001 mM).

II. The Warburg effect describes how cancer cells use aerobic glycolysis to generate biosynthetic precursors for rapid cell division, despite its lower ATP efficiency.

III. During hypoglycemia in pancreatic α-cells, decreased ATP/ADP ratio opens ATP-sensitive K+ channels, leading to membrane depolarization and glucagon secretion.

A) 1 and 2 are true 3 is false

B) 1 and 3 are true 2 is false

C) 2 and 3 are true 1 is false

D) 1 is true, 2 and 3 are false

E) All are true

A researcher adds a high concentration of fructose 2,6 bisphosphate to a purified phosphofructokinase-1 enzyme assay. Which kinetic change wold be observed

A) The Vmax increases but the Km remains unchanged

B) The sigmoidal substrate saturation curve shifts to a hyperbolic curve with decreased Km

C) The enzyme becomes insensitive to ATP inhibition but maintains the same Vmax

D) Both Vmax and Km increase proportionally

E) The enzyme swiches from positive to negative cooperativitiy

B

Why does the enolase reaction (2-phosphoglycertate → phosphoenolpyruvate) result in a product with much higher phosphoryl transfer potential despite having a delta G degree of only + 1.8 kJ/mol

A) The removeal of water concentrates the phosphate group, increasing its energy

B) The enol form of pyruvate is unstable and tautomerizes to the keto form, releasing energy that is trapped in the phosphate bond

C) Mg² cofactor binding increases the enrgy of the phosphate bond

D) The reaction is coupled to ATP hydrolysis which provide the energy
E) The phosphate group moves from C-2 to C-3 increasing trasnfer potential

B

When insulin is released, it acts to increase the absorption of glucose into skeletal muscle predominantly through which of the following transporters?

A) GLUT 1

B) GLUT 2

C) GLUT 3

D) GLUT 4

E) GLUT 5

D

An investigator is measuring the activity of various enzymes involved in reactions of intermediary metabolism. One of the enzymes has greatly decreased activity compared to reference values. The buffer of the assay contains citrate. Which of the following enzymes will most likely be directly affected by the use of citrate?

A) Fructose 2,6 bisphosphatase

B) Isocitrate dehydrogenase

C) Phosphofructokinase - 1

D) Pyruvate Carboxylase

E) Glycogen phosphorylase

C

A researcher isolates mitochondria and adds pyruvate, CoA, NAD⁺, and thiamine pyrophosphate (TPP). She observes CO₂ production but no acetyl-CoA formation. Which additional cofactor is most likely missing?

A) FAD
B) Lipoic Acid

C) Biotin

D) Pyridoxal Phosphate

E) NADP+

B

The pyruvate dehydrogenase complex (PDC) is regulated by both allosteric effectors and covalent modification. Which of the following conditions would result in MAXIMUM PDC activity?

A) High ATP, high NADH, phosphorylated E1

B) High ADP, high NAD+ dephosphorylated E1

C) High acetyl-CoA, low CoA, dephosphorylated E1

D) High ATP, high NAD+ phosphorylated E1

E) High ADP, high NADH, phosphorylated E1

B

Citrate synthase catalyzes the first committed step of the TCA cycle. Which of the following best explains why this reaction is virtually irreversible under cellular conditions?

A) The reaction requires ATP hydrolysis

B) The delta G degree is highly positive (+31.4 kJ/mol)

C) The thioester bond of acetyl- CoA is hydrolyzed, releasing significant free energy

D) The reaction produces CO2 which escapes the system

E) Citrate is immediately converted to isocitrate

C

Which statements are true and which are false?

I. The chemical logic of the TCA cycle requires condensation of acetyl-CoA with oxaloacetate because acetate lacks a β-carbon necessary for C-C bond cleavage.

II. Citrate synthase catalyzes the condensation of acetyl-CoA and oxaloacetate to form citrate with a ΔG°' of -31.4 kJ/mol, making it the first committed step of the TCA cycle.

III. In the citrate synthase reaction, citryl-CoA is formed as an intermediate, and the hydrolysis of this intermediate releases CoA-SH.

A) 1 is true ; 2 and 3 are false

B) 1 and 2 are true ; 3 is false

C) 2 and 3 are true ; 1 is false

D) 1 and 3 are true ; 2 is false

E) All are true

E

Which statements are true and which are false?

I. Aconitase catalyzes the reversible isomerization of citrate to isocitrate via a cis-aconitate intermediate, and requires an iron-sulfur [4Fe-4S] cluster for activity.

II. The aconitase reaction moves the hydroxyl group from a tertiary carbon to a secondary carbon because tertiary alcohols cannot be oxidized while secondary alcohols can.

III. Fluoroacetate is a lethal poison because it is converted to fluorocitrate, which irreversibly inhibits isocitrate dehydrogenase.

A) 1 and 2 are true ; 3 is false

B) 1 and 3 are true '; 2 is false

C) 2 and 3 are true ; 1 is falses

D) 1 is true ; 2 and 3 are false

E) All are true

A

Which statements are true and which are false?

I. Isocitrate dehydrogenase catalyzes the first oxidative decarboxylation in the TCA cycle, producing α-ketoglutarate, CO₂, and the first NADH of the cycle.

II. The isocitrate dehydrogenase reaction proceeds through an oxalosuccinate intermediate and is a major regulatory point, being activated by ADP and Ca²⁺.

III. The α-ketoglutarate dehydrogenase complex is structurally and mechanistically similar to the pyruvate dehydrogenase complex, using the same five coenzymes and catalyzing oxidative decarboxylation.

A) 1 and 2 are true ; 3 is false

B) 1 and 3 are true '; 2 is false

C) 2 and 3 are true ; 1 is falses

D) 1 is true ; 2 and 3 are false

E) All are true

E)

Which statements are true and which are false?

I. Succinate dehydrogenase is unique among TCA cycle enzymes because it is the only one embedded in the inner mitochondrial membrane and directly participates in the electron transport chain as Complex II.

II. Succinate dehydrogenase uses FAD rather than NAD⁺ as its electron acceptor because the oxidation of a -CH₂-CH₂- to -CH=CH- bond is not energetically favorable enough to reduce NAD⁺.

III. Malonate is a competitive inhibitor of succinate dehydrogenase because it is a structural analog of succinate.

A) 2 and 3 are true ; 1 is false

B) 1 and 2 are true ; 3 is false

C) 1 is true ; 2 and 3 are false

D) 1 and 3 are true ; 2 is false

E) All are true

E

Isocitrate dehydrogenase is allosterically activated by ADP and Ca²+. IN which physiological situation would both of these activators be elecated simultaneouslty

A) During prolonged fasting

B) During active muscle contration

C) During sleep

D) Following a high carbohydrate meal

E) During insulin singaling in adipocytes

B

In pancreatic B-cells, approximately half of the pyruvate from glycolysis is diverted to OAA by pyruvate carboxylase. What is the primary purpose of this anaplerotic flux

A) To generate ATP for insulin secretion

B) To produce NADPH and other signaling metabolites that trigger insulin release

C) To store excess glucose as glycogen for later insulin release

D) To prevent pyruvate from entering the TCA cycle

E) To generate gluconeogenic precursors for insulin release.

The malate dehydrogenase reaction has a delta G degree of +29.7 kJ/mol, yet it proceeds in the forward direction in vivo. Which factor is most important for driving this thermodynamically unfavorable reaction?

A) High temperature in the itochondrial matrix

B) Coupling to ATP hydrolysis

C) Rapid removal of OAA by citrate synthase

D) High concentration of NAD+

E) Allosteric activation by ADP

C

A 2-yearold child presents wuth developmental regression, hyotonia (decreased muscle tone), and lactic acidosis (buildup of lactic acid in the bloodstream that leads to a decreased blood pH). Genetic testing reveals a mutation in the PDHA1 gene encoding the E1alpha subunit of pyruvate dehydrogenase. Brain MRI shows bilateral lesions in the basal ganglia.

Which metabolic profile would you expect to find in this patient’s blood?

A) Elevated pyruvate, elevated lactate, elevated alanine

B) Decreased pyruvate, decreased lactate, elevated ketones

C) Elevated citrate, elevated isocitrate, decreased lactate

D) Decreased pyruvate, elevated acetyl-CoA, normal lactate

E) Normal pyruvate, normal lactate, elevated ammonia

A

A patient with a rare genetic disorder has a deficiency in the enzyme that catalyzes step 6 of the citric acid cycle ( succinate dehydrogenase/ Complex II) Paradoxically, despite this being a catabolic pathway defect, the patient also shows impaired biosynthesis of certain macromolecules.

Based on the dual roles of the citric acid cycle intermediates, which combination of biosynthetic pathways would most likely be affected in this patient?

A) Fatty acid synthesis (from citrate) and amino acid synthesis (from oxaloacetate only

B) Cholesterol synthesis (from citrate) and nucleotide syntehsis (from GTP) only

C) Amino acid synthesis (from OAA) and DNA / RNA synthesis (from OAA) primarily

D) Fatty acid synthesis, lipid synthesis, and cholesterol synthesis (all from citrate) with secondary effects on amino acid and nuclei acid synthesis (from OAA)

E) Protein synthesis (from GTP) and membrane lipid synthesis (from succinate) only

D

Pyruvate carboxylase is the most important anaplerotic enzyme. This enzyme requires which vitamin-derived coenzyme?

A) Thiamine (B1)

B) Riboflavin (B2)

C) Niacin (B3)

D) Pantothenic acid (B5)

E) Biotin (B7)

E

A researcher is studying the α-ketoglutarate dehydrogenase complex (Step 4 of the citric acid cycle) and observes that this multi-enzyme complex uses "flexible tethers" to efficiently move reactants between active sites. A mutation in one of the tethering domains results in decreased efficiency of electron transfer within the complex.

Which of the following would be the MOST LIKELY immediate consequence of this mutation on cellular metabolism

A) Decreased production of GTp at the succinyl-CoA synthetase step due to reduced substrate availability

B) Accumulation of citrate in the mitochondrial matrix leading to increased fatty acid biosynthesis

C) Increased production of CO2 as the complex attempts to compensate for reduced efficiency

D) Direct inhibition of Complex II of the electron transport chain due to feedback mechanisms

E) Reduced electron delivery to the elctron transport chain with normal Co2 production from this step

A)

Which of the following correctly pairs a TCA cucle enzyme with its inhibitor

A) Citrate synthase - Malonate

B) Aconitase - ATP

C) Isocitrate dehydrogenase - Fluorocitrate

D) a- Ketoglutarate dehydrogenase - Succinyl CoA

E) Succinate dehydrogenase - Citrate

D

A 55-year-old man with chronic alcoholism presents with confusion, ataxia (lack of coordination of voluntary muscle movements), and ophthalmoplegia (weakness or paralysis of the eye muscles). Laboratory studies show elevated blood pyruvate and α-ketoglutarate levels. You suspect thiamine deficiency.

Which enzymes are MOST directly affected by thiamine deficiency in the TCA cycle and related pathways?

A) Citrate synthase and aconitase

B) Pyruvate dehydrogenase and a-ketoglutarate dehydrogenase

C) Succinate dehydrogenase and fumarase

D) Malate dehydrogenase and isocitrate dehydrogenase

E) Pyruvate carboxylase and succinyl-CoA synthetase

B)

A 55-year-old man with chronic alcoholism presents with confusion, ataxia (lack of coordination of voluntary muscle movements), and ophthalmoplegia (weakness or paralysis of the eye muscles). Laboratory studies show elevated blood pyruvate and α-ketoglutarate levels. You suspect thiamine deficiency.

Which enzymes are MOST directly affected by thiamine deficiency in the TCA cycle and related pathways?

A) Accumulation of fumarate and decreased citrate

B) Accumulation of succinate and imparied electron entry into the ETC at Complex II

C) Accumulation of succinyl-CoA and decreased GTP production

D) Decreased succinate and increased a - ketoglutarate

E) Complete loss of mitochondrial ATP production

B)

Researchers studying a tumor find that cancer cells export large amounts of citrate to the cytoplasm, even under conditions of adequate energy supply. The cells also show increased expression of ATP-citrate lyase, an enzyme that converts citrate into acetyl‑CoA and oxaloacetate in the cytosol.

What is the most likely purpose of citrate export in these cancer cells?

A) To generate ATP in the cytoplasm

B) To provide acetyl-CoA for fatty acid synthesis

C) To reduce TCA cycle activity and decrease oxidative stress

D) To buffer cytoplasmic pH

E) To inhibit glycolysis through feedback inhibition

B)

Which statements are true and which are false?

I. The allosteric regulation of PDC follows the logic that high energy status (high ATP, NADH, acetyl-CoA) inhibits the complex, while low energy status (high ADP, NAD⁺, CoA) activates it.

II. Odd-chain fatty acid oxidation produces propionyl-CoA, which is ultimately converted to succinyl-CoA, representing an anaplerotic pathway.

III. The TCA cycle occurs in the cytoplasm of eukaryotic cells, where it is closely associated with the electron transport chain

A) 1 and 2 are true ; 3 is false

B) 1 and 3 are true ; 2 is false

C) 2 and 3 are true ; 1 is false

D) 1 is true 2 and 3 are false

E) All are true

Which statements are true and which are false?

I. In pancreatic β-cells, approximately half of the pyruvate from glycolysis is converted to oxaloacetate by pyruvate carboxylase, supporting a pyruvate/malate cycle that generates signaling molecules.

II. NADPH and other metabolites generated from the pyruvate/malate cycle in pancreatic β-cells act as intracellular messengers that help trigger insulin release.

III. Exercise increases anaplerotic activity in peripheral tissues, which contributes to reduced fatty acid oxidation and decreased insulin sensitivity.

A) 1 and 2 are true; 3 is false

B) 1 and 3 are true ; 2 is false

C) 2 and 3 are true ; 1 is false

D) 1 is true ; 2 and 3 are false

E) All are true

A)

During electron transport, protons are pumped from the mitochondrial matrix to the intermembrane space by Complexes I II III IV. Which complex does not pump protons?

A) Complex 1 (NADH-ubiquinone oxidoreductase)
B) Complex 2 (Succinate dehydrogenase)

C) Complex 3 (Ubiqinone - cytochrome c oxidoreductase)
D) Complex 4 (Cytochrome c oxidase)

E) All four complexes pump protons

Ubiquinone (Coenzyme Q) serves as a mobile electron carrier in the inner mitochondrial membrane. Which property makes ubiquinone uniquely suited for this role?

A) It is water-soluble protein that diffuses through the inter membrane space

B) It contains a heme group that can accept two electrons simultaneously

C) It is lipid soluble and can accept electrons from both Complex 1 and Complex 3

D) It directly transfers electron to oxygen

E) It is covalnetly attached to Complex 3

C)

The Q cycle in Complex III is necessary to solve an electron-handling problem. What is this problem

A) Complex III cannot accept electrons directly from NADH

B) Ubiquinol (QH2) carries 2 electrons, but cytochrome c can only accept 1 electron at a time

C) Protons must be transported against their concentration gradient

D) Oxgen requires 4 electrons for complete reduction

E) The Rieske iron-sulfur protein cannot redue heme groups

B

Which statements are true and which are false?

I. Complex I is the largest ETC complex (~980 kDa, 44 subunits) and contains FMN and multiple Fe-S clusters. The electron path through Complex I is: NADH → FMN → Fe-S clusters → ubiquinone.

II. Complex II (succinate dehydrogenase) is unique because it participates in both the TCA cycle and the electron transport chain, and it pumps 4 H⁺ per pair of electrons like Complex I.

III. Fe-S clusters function as one-electron carriers (Fe³⁺ + e⁻ ⇌ Fe²⁺), bridging the gap between two-electron carriers (NADH, FADH₂) and one-electron carriers (cytochromes).

A) 1 and 2 are true ; 3 is false

B) 1 is true ; 2 and 3 are false

C) All are true

D) 1 and 3 are true ; 2 is false

E) 2 and 3 are true ; 1 is false

D)

Which statements are true and which are false?

I. Cyanide inhibits Complex IV by binding to Fe³⁺ in heme a₃, while carbon monoxide inhibits Complex IV by binding to Fe²⁺ in heme a₃—both prevent oxygen binding and halt the entire electron transport chain.

II. Oligomycin inhibits ATP synthase by blocking the F₀ proton channel; when oligomycin is present, electron transport also stops because the proton gradient builds up and cannot be dissipated.

III. Rotenone inhibits Complex I by blocking electron transfer from Fe-S clusters to ubiquinone; however, electrons from FADH₂ (via Complex II) can still enter the chain at ubiquinone.

A) 1 and 2 are true ; 3 is false

B) 1 is true ; 2 and 3 are false

C) All are true

D) 1 and 3 are true ; 2 is false

E) 2 and 3 are true ; 1 is false

C

Which statements are true and which are false?

I. The malate-aspartate shuttle transfers electrons from cytosolic NADH to mitochondrial NADH, yielding ~2.5 ATP per cytosolic NADH, and is the primary shuttle in liver, kidney, and heart.

II. The glycerophosphate shuttle transfers electrons from cytosolic NADH to mitochondrial FAD (at Complex II), yielding ~1.5 ATP per cytosolic NADH, and is faster but less efficient than the malate-aspartate shuttle.

III. The inner mitochondrial membrane is freely permeable to NADH, so shuttle systems are only needed when the cell requires rapid ATP production.

A) 1 and 2 are true ; 3 is false

B) 1 is true ; 2 and 3 are false

C) All are true

D) 1 and 3 are true ; 2 is false

E) 2 and 3 are true ; 1 is false

A

Which statements are true and which are false?

I. The malate-aspartate shuttle transfers electrons from cytosolic NADH to mitochondrial NADH, yielding ~2.5 ATP per cytosolic NADH, and is the primary shuttle in liver, kidney, and heart.

II. The glycerophosphate shuttle transfers electrons from cytosolic NADH to mitochondrial FAD (at Complex II), yielding ~1.5 ATP per cytosolic NADH, and is faster but less efficient than the malate-aspartate shuttle.

III. The inner mitochondrial membrane is freely permeable to NADH, so shuttle systems are only needed when the cell requires rapid ATP production.

A) Complex 2 and 4

B) the ubiquinone pool and cytochrome c

C) Complex 1 and 3

D) ATP synthase and ATP - ADP translocase

E) only at complex 4 during oxygen reduction

C

Pyruvate carboxylase, the first enzyme in the gluconeogenic bypass of pyruvate kinase, requires which vitamin- derived cofactor

A) Thiamine pyrophosphate (TPP)

B) Biotin

C) Pyridoxial phosphate (PLP)

D)FAD

E) Cobalamin

B

In the fasted state, glucagon signaling leads to decreased levels of fructose-2,6-bisphosphate in the liver. This regulatory molecule:

A) Is an intermediate in both glycolysis and gluconeogensis

B) Activates FBPase-1 and inhibits PFK-1

C) Is synthesized and degreade by a single bifunctional enzyme (PFK-2/FBPase-2)

D) Increase when PKA phosphorylates the bifunctional enzyme

E) Has no effect on gluconeogenesis

C)

In the fasted state, glucagon signaling leads to decreased levels of fructose-2,6-bisphosphate in the liver. This regulatory molecule:

A) pyruvate

B) OAA
C) Dihydroxyacetone phosphate (DHAP)

D) Fructose 6 phosphate

E) Glucose 6 phosphate

C

The Cori cycle describes the metabolic cooperation between muscle and liver. Which statement best describes this cycle?

A) Muscle exports glucose to the liver for storage as glycogen

B) Lactate produced in muscle is transported to the liver, converted to glucose via gluconeogenesis, and returned to muscle

C) Alanine is the primary carrier molecule between muscle and liver

D) The cycle generates net ATP for the body

E) The cycle only operates during the fed state

B

Muscle glycogen cannot directly contribute to blood glucose maintenance because muscle lacks:

A) Glycogen phosphorylase

B) Phosphoglucomutase

C) Glucose - 6 - phosphatase

D) Hexokinase
E) Glut 4 transporters

C)

Which statements are true and which are false?

I. The debranching enzyme has two activities: a transferase that moves a block of 3 glucose residues, and an α-1,6-glucosidase that hydrolyzes the branch-point glucose, releasing it as free glucose.

II. Glycogen phosphorylase can completely degrade glycogen without the assistance of any other enzymes.

III. The branching enzyme creates α-1,6 branch points by transferring a block of approximately 7 glucose residues from a linear chain.

A) 1 and 2 are true ; 3 is false

B) 1 is true ; 2 and 3 are false

C) All are true

D) 1 and 3 are true ; 2 is false

E) 2 and 4 are true ; 1 is false

D

Which statements are true and which are false?

I. Glycogen synthase a (dephosphorylated) is the active form, while glycogen synthase b (phosphorylated) is less active—the opposite pattern from glycogen phosphorylase.

II. Phosphoprotein phosphatase 1 (PP1) dephosphorylates and inactivates glycogen synthase while activating glycogen phosphorylase.

III. Glucose-6-phosphate can partially activate glycogen synthase b by promoting a conformational change that makes it a better substrate for PP1.

A) 1 and 2 are true ; 3 is false

B) 1 is true ; 2 and 3 are false

C) All are true

D) 1 and 3 are true; 2 is false

E) 2 and 3 are true ; 1 is false

D)

Which statements are true and which are false?

I. The energy cost of gluconeogenesis from two pyruvate molecules is 4 ATP + 2 GTP + 2 NADH, making it significantly more expensive than the 2 ATP produced by glycolysis.

II. Acetyl-CoA is a gluconeogenic precursor because it can be converted to oxaloacetate in the TCA cycle.

III. Acetyl-CoA activates pyruvate carboxylase, signaling that fatty acids are being oxidized and glucose should be spared through gluconeogenesis.

A) 1 and 2 are true ; 3 is false

B) 1 is true ; 2 and 3 are false

C) All are true

D) 1 and 3 are true ; 2 is false

E) 2 and 3 are true ; 1 is false

Glycogen phosphorylase cleaves alpha 1,4 glycosidic bonds using which mechanism

A) Hydrolysis, releasing free glucose

B) Phosphorolysis, producing glycose 1 phosphate

C) Oxidation, producing gluconic aicd

D) Transamination, linking glycogen to amino acid metabolism

E) Reduction, requiring NADH

B

In liver, glycogen phosphorylase a (the active, phosphorylated form) is subject to an additional regulatory mechanism not found in muscle. High blood glucose:

A) Further activates phosphorylase a by a by stabilizing its conformation

B) Inhibits phosphorylase a allosterically and promotes its dephosphorylation by PP1

C) Stimulates PKA to maintain phosphorylase in its active form

D) Has no direct effect on phosphorylase; only insulin regulates it

E) Converts phorphorylase a to the b form through AMP binding

B

Insulin promotes glycogen synthesis by activating a signaling cascade that ultimately leads to:

A) Activation of GSK3 and phorphorylation of glycogen synthase

B) Inactivation of GSK3 via PKB / Akt allowing PP1 to dephosphorylate and activate glycogen synthase

C) Direct phosphorylation of glycogen synthase by the insulin receptor

D) Actiation of phosphorylase kinase

E) Increased cAMP levels and PKA activation

B

Which statements are true and which are false?

I. Fructose-2,6-bisphosphate activates PFK-1 (glycolysis) and inhibits FBPase-1 (gluconeogenesis), ensuring reciprocal regulation of these pathways.

II. Glucagon signaling phosphorylates the bifunctional enzyme PFK-2/FBPase-2, which increases PFK-2 activity and decreases FBPase-2 activity.

III. AMP allosterically activates PFK-1 and inhibits FBPase-1, coordinating both pathways according to cellular energy status.

A) 1 and.2 are true ; 3 is false

B) 1 is true ; 2 and 3 are false

C) All are true

D) 1 and 3 are true ; 2 is false

E) 2 and 3 are true ; 1 is false

D

Glycogenin is essential for glycogen synthesis because it:

A) Phosphorylates glycogen synthase to activate it

B) Serves as the primer for new glycogen molecules by autoglycosylation

C) Creates the alpha 1,6 branch points in glycogen

D) Transfers glucose from UDP-glucose to the growing chain

E) Dephosphorylates glycogen phosphorylase

B