Untitled Deck

Question 1

Which molecule serves as the common entry point for carbohydrates, fats, and proteins into the Krebs cycle?
A) Pyruvate

B) Acetyl-CoA

C) Oxaloacetate

D) Citrate

Answer 1

B) Acetyl-CoA

Question 2

Where in the cell does the Krebs cycle occur?
A) Cytosol

B) Mitochondrial matrix

C) Endoplasmic reticulum

D) Nucleus

Answer 2

B) Mitochondrial matrix

Question 3

Which of the following is a direct product of the Krebs cycle?
A) ATP

B) NADH

C) Glucose

D) Lactate

Answer 3

A) ATP

Question 4

What is the primary purpose of the NADH and FADH₂ produced in the Krebs cycle?
A) Serve as substrates for gluconeogenesis

B) Act as antioxidants

C) Donate electrons to the electron transport chain

D) Convert into glucose in the liver

Answer 4

C) Donate electrons to the electron transport chain

Question 5

Which enzyme catalyzes the conversion of pyruvate to acetyl-CoA?
A) Pyruvate carboxylase

B) Pyruvate dehydrogenase

C) Lactate dehydrogenase

D) Pyruvate kinase

Answer 5

B) Pyruvate dehydrogenase

Question 6

A deficiency in which vitamin would most directly impair the function of the pyruvate dehydrogenase complex?
A) Vitamin B1 (Thiamine)

B) Vitamin B6 (Pyridoxine)

C) Vitamin B12 (Cobalamin)

D) Vitamin C (Ascorbic acid)

Answer 6

A) Vitamin B1 (Thiamine)

Question 7

Which of the following enzymes is inhibited by high levels of ATP and NADH?

A) Isocitrate dehydrogenase

B) Citrate synthase

C) Aconitase

D) Fumarase

Answer 7

A) Isocitrate dehydrogenase

Question 8

In the regulation of gluconeogenesis, which enzyme is activated by acetyl-CoA?
A) Pyruvate carboxylase

B) Phosphoenolpyruvate carboxykinase (PEPCK)

C) Fructose-1,6-bisphosphatase

D) Glucose-6-phosphatase

Answer 8

A) Pyruvate carboxylase

Question 9

Which of the following conditions is characterized by a deficiency of glucose-6-phosphatase?

A) McArdle disease

B) Von Gierke disease

C) Pompe disease

D) Cori disease

Answer 9

B) Von Gierke disease

Question 10

Which TCA cycle intermediate serves as a precursor for heme synthesis?
A) Citrate

B) α-Ketoglutarate

C) Succinyl-CoA

D) Fumarate

Answer 10

C) Succinyl-CoA

Question 11

A 6-month-old infant presents with poor feeding, hypotonia, and elevated serum lactate. Genetic testing reveals a mutation in the PDHA1 gene. Which enzyme is deficient?

A) Pyruvate carboxylase

B) Pyruvate dehydrogenase

C) Lactate dehydrogenase

D) Glucose-6-phosphatase

Answer 11

B) Pyruvate dehydrogenase

Question 12

A patient with chronic alcoholism develops confusion, ataxia, and ophthalmoplegia. Which vitamin deficiency is most likely responsible for these symptoms?

A) Vitamin B2 (Riboflavin)

B) Vitamin B3 (Niacin)

C) Vitamin B1 (Thiamine)

D) Vitamin B6 (Pyridoxine)

Answer 12

C) Vitamin B1 (Thiamine)

Question 13

During prolonged fasting, which of the following processes provides substrates for gluconeogenesis?
A) Glycogenolysis

B) Lipolysis

C) Glycolysis

D) Protein synthesis

Answer 13

B) Lipolysis

Question 14

A patient has a deficiency in fructose-1,6-bisphosphatase. Which metabolic pathway is directly impaired?
A) Glycolysis

B) Gluconeogenesis

C) Glycogenesis

D) Pentose phosphate pathway

Answer 14

B) Gluconeogenesis

Question 15

Which of the following enzymes is responsible for the conversion of oxaloacetate to phosphoenolpyruvate in gluconeogenesis?
A) Pyruvate carboxylase

B) Phosphoenolpyruvate carboxykinase (PEPCK)

C) Fructose-1,6-bisphosphatase

D) Glucose-6-phosphatase

Answer 15

B) Phosphoenolpyruvate carboxykinase (PEPCK)

Question 16

Which of the following tissues lacks the enzyme glucose-6-phosphatase, making it unable to contribute to blood glucose levels via gluconeogenesis?
A) Liver

B) Kidney

C) Muscle

D) Intestinal epithelium

Answer 16

C) Muscle

Question 17

In the context of gluconeogenesis, which of the following substrates can be used to generate glucose?
A) Acetyl-CoA

B) Glycerol

C) Palmitate

D) Ketone bodies

Answer 17

B) Glycerol

Question 18

Which of the following best explains why red blood cells rely solely on glycolysis for ATP production?
A) Lack of glucose transporters

B) Absence of mitochondria

C) High oxygen affinity

D) Presence of lactate dehydrogenase

Answer 18

B) Absence of mitochondria

Question 19

A patient presents with hypoglycemia, lactic acidosis, hyperuricemia, and hepatomegaly. Which enzyme deficiency is most consistent with these findings?
A) Glucose-6-phosphatase

B) Debranching enzyme

C) Glycogen phosphorylase

D) Branching enzyme

Answer 19

A) Glucose-6-phosphatase

Question 20

Which of the following enzymes is responsible for the first committed step of gluconeogenesis?

A) Pyruvate carboxylase

B) Phosphoenolpyruvate carboxykinase

C) Fructose-1,6-bisphosphatase

D) Glucose-6-phosphatase

Answer 20

A) Pyruvate carboxylase

Question 21

A patient with a deficiency in pyruvate carboxylase would have difficulty synthesizing which of the following molecules?

A) Acetyl-CoA

B) Oxaloacetate

C) Citrate

D) Succinyl-CoA

Answer 21

B) Oxaloacetate

Question 22

Which vitamin is a cofactor for the enzyme transketolase in the pentose phosphate pathway?

A) Vitamin B1 (Thiamine)

B) Vitamin B2 (Riboflavin)

C) Vitamin B3 (Niacin)

D) Vitamin B6 (Pyridoxine)

Answer 22

A) Vitamin B1 (Thiamine)

Question 23

In the TCA cycle, which enzyme catalyzes the conversion of isocitrate to α-ketoglutarate?

A) Aconitase

B) Isocitrate dehydrogenase

C) α-Ketoglutarate dehydrogenase

D) Succinate dehydrogenase

Answer 23

B) Isocitrate dehydrogenase

Question 24

Which of the following best describes the role of the malate-aspartate shuttle?

A) Transports acetyl-CoA into the mitochondria

B) Transfers electrons from NADH into the mitochondria

C) Facilitates the export of ATP from the mitochondria

D) Transports pyruvate into the mitochondria

Answer 24

B) Transfers electrons from NADH into the mitochondria

Question 25

A deficiency in which of the following enzymes would impair both the TCA cycle and the electron transport chain? A) Pyruvate dehydrogenase B) Succinate dehydrogenase C) Isocitrate dehydrogenase D) α-Ketoglutarate dehydrogenase

Answer 25

B) Succinate dehydrogenase

Question 26

Which of the following is the rate-limiting enzyme of the TCA cycle? A) Citrate synthase B) Isocitrate dehydrogenase C) α-Ketoglutarate dehydrogenase D) Succinate dehydrogenase

Answer 26

B) Isocitrate dehydrogenase

Question 27

During fasting, which hormone promotes gluconeogenesis in the liver? A) Insulin B) Glucagon C) Epinephrine D) Cortisol

Answer 27

B) Glucagon

Question 28

Which of the following amino acids is purely ketogenic? A) Leucine B) Isoleucine C) Phenylalanine D) Tyrosine

Answer 28

A) Leucine

Question 29

Which of the following enzymes is shared between the TCA cycle and the electron transport chain? A) Succinate dehydrogenase B) Malate dehydrogenase C) Aconitase D) Fumarase

Answer 29

A) Succinate dehydrogenase

Question 30

Which of the following best explains why fatty acids cannot be used for gluconeogenesis? A) They are not converted to acetyl-CoA B) Acetyl-CoA cannot be converted to pyruvate C) Fatty acids are not oxidized in the mitochondria D) They are preferentially used for ketone body synthesis

Answer 30

B) Acetyl-CoA cannot be converted to pyruvate

Question 31

A 24-year-old woman presents with diarrhea, dysphagia, jaundice, and white transverse lines on her fingernails (Mee's lines). She is diagnosed with arsenic poisoning. Arsenic inhibits which of the following enzymes? A. Citrate synthase B. Isocitrate dehydrogenase C. Malate dehydrogenase D. Succinate dehydrogenase E. α-Ketoglutarate dehydrogenase complex

Answer 31

E. α-Ketoglutarate dehydrogenase complex Explanation: Arsenic binds to lipoic acid, a cofactor essential for the function of α-ketoglutarate dehydrogenase complex, impairing the TCA cycle and leading to energy production deficits.

Question 32

A chronic alcoholic presents with confusion, ataxia, and ophthalmoplegia. Which TCA cycle enzyme is most affected due to thiamine deficiency? A. Citrate synthase B. Isocitrate dehydrogenase C. α-Ketoglutarate dehydrogenase D. Succinate dehydrogenase E. Malate dehydrogenase

Answer 32

C. α-Ketoglutarate dehydrogenase Explanation: Thiamine (Vitamin B1) is a cofactor for α-ketoglutarate dehydrogenase. Deficiency impairs its function, leading to accumulation of α-ketoglutarate and reduced ATP production.

Question 33

A patient ingests a rodenticide containing fluoroacetate and develops severe metabolic disturbances. Fluoroacetate inhibits which TCA cycle enzyme? A. Aconitase B. Isocitrate dehydrogenase C. α-Ketoglutarate dehydrogenase D. Succinate dehydrogenase E. Malate dehydrogenase

Answer 33

A. Aconitase Explanation: Fluoroacetate is converted to fluorocitrate, which inhibits aconitase, halting the TCA cycle and leading to energy depletion.

Question 34

Which TCA cycle enzyme also functions as Complex II in the electron transport chain? A. Citrate synthase B. Isocitrate dehydrogenase C. α-Ketoglutarate dehydrogenase D. Succinate dehydrogenase E. Malate dehydrogenase

Answer 34

Answer: D. Succinate dehydrogenase Explanation: Succinate dehydrogenase participates in both the TCA cycle and the electron transport chain as Complex II, facilitating the transfer of electrons from FADH₂.

Question 35

Each NADH molecule produced in the TCA cycle yields how many ATP molecules via oxidative phosphorylation? A. 1 ATP B. 2 ATP C. 2.5 ATP D. 3 ATP E. 4 ATP

Answer 35

Answer: C. 2.5 ATP Explanation: Each NADH contributes approximately 2.5 ATP molecules during oxidative phosphorylation.

Question 36

Which molecule inhibits the rate-limiting enzyme of the TCA cycle? A. ADP B. NAD⁺ C. ATP D. Calcium E. Acetyl-CoA

Answer 36

Answer: C. ATP Explanation: ATP inhibits isocitrate dehydrogenase, the rate-limiting enzyme of the TCA cycle, signaling sufficient energy levels and reducing cycle activity.

Question 37

Which TCA cycle reaction involves substrate-level phosphorylation? A. Citrate to isocitrate B. α-Ketoglutarate to succinyl-CoA C. Succinyl-CoA to succinate D. Fumarate to malate E. Malate to oxaloacetate

Answer 37

Answer: C. Succinyl-CoA to succinate Explanation: This step generates GTP (which can be converted to ATP) via substrate-level phosphorylation.

Question 38

Which enzyme catalyzes an anaplerotic reaction replenishing TCA cycle intermediates? A. Pyruvate carboxylase B. Pyruvate dehydrogenase C. Citrate synthase D. Isocitrate dehydrogenase E. Malate dehydrogenase

Answer 38

Answer: A. Pyruvate carboxylase Explanation: Pyruvate carboxylase converts pyruvate to oxaloacetate, replenishing TCA cycle intermediates.

Question 39

Citrate exported from mitochondria to the cytosol is used for the synthesis of which molecule? A. Glucose B. Amino acids C. Fatty acids D. Nucleotides E. Cholesterol

Answer 39

Answer: C. Fatty acids Explanation: Citrate carries acetyl-CoA equivalents to the cytosol for fatty acid synthesis.

Question 40

Which TCA cycle intermediate is a precursor for heme synthesis? A. Citrate B. α-Ketoglutarate C. Succinyl-CoA D. Fumarate E. Malate

Answer 40

Answer: C. Succinyl-CoA Explanation: Succinyl-CoA combines with glycine to initiate heme synthesis.

Question 41

A 3-year-old boy presents with hypotonia, lactic acidosis, and developmental delay. Laboratory studies reveal elevated lactate and pyruvate levels. Genetic testing shows a deficiency in the pyruvate dehydrogenase complex. Which of the following cofactors is NOT required for the proper function of this enzyme complex? A) Thiamine (Vitamin B1) B) Lipoic acid C) Pantothenic acid (Vitamin B5) D) Niacin (Vitamin B3) E) Ascorbic acid (Vitamin C)

Answer 41

Answer: E) Ascorbic acid (Vitamin C) Explanation: The pyruvate dehydrogenase complex requires five cofactors: thiamine (B1), lipoic acid, coenzyme A (from pantothenic acid, B5), FAD (from riboflavin, B2), and NAD+ (from niacin, B3). Ascorbic acid (Vitamin C) is not involved in this complex.

Question 42

A patient is found to have elevated levels of citrate in the cytosol. Which of the following processes is most likely to be upregulated as a result? A) Glycolysis B) Gluconeogenesis C) Fatty acid synthesis D) β-oxidation E) Ketogenesis

Answer 42

Answer: C) Fatty acid synthesis Explanation: Citrate exported from the mitochondria to the cytosol serves as a substrate for ATP citrate lyase, which converts citrate back to acetyl-CoA, a precursor for fatty acid synthesis.

Question 43

Which of the following enzymes of the TCA cycle is also part of the electron transport chain? A) Isocitrate dehydrogenase B) α-Ketoglutarate dehydrogenase C) Succinate dehydrogenase D) Malate dehydrogenase E) Fumarase

Answer 43

Answer: C) Succinate dehydrogenase Explanation: Succinate dehydrogenase is unique as it functions in both the TCA cycle and the electron transport chain (Complex II), where it facilitates the transfer of electrons from FADH2 to coenzyme Q.

Question 44

A 24-year-old woman presents with symptoms of arsenic poisoning. Arsenic inhibits which of the following enzymes in the TCA cycle? A) Citrate synthase B) Isocitrate dehydrogenase C) α-Ketoglutarate dehydrogenase D) Succinate dehydrogenase E) Malate dehydrogenase

Answer 44

Answer: C) α-Ketoglutarate dehydrogenase Explanation: Arsenic binds to lipoic acid, a cofactor for α-ketoglutarate dehydrogenase, inhibiting its activity and disrupting the TCA cycle.

Question 45

Which of the following TCA cycle intermediates is a precursor for heme synthesis? A) Citrate B) α-Ketoglutarate C) Succinyl-CoA D) Fumarate E) Malate

Answer 45

Answer: C) Succinyl-CoA Explanation: Succinyl-CoA combines with glycine to form δ-aminolevulinic acid, the first step in heme synthesis.

Question 46

In the TCA cycle, which step directly generates GTP (or ATP in some tissues)? A) Isocitrate to α-ketoglutarate B) α-Ketoglutarate to succinyl-CoA C) Succinyl-CoA to succinate D) Succinate to fumarate E) Malate to oxaloacetate

Answer 46

Answer: C) Succinyl-CoA to succinate Explanation: The conversion of succinyl-CoA to succinate by succinyl-CoA synthetase generates GTP (or ATP), a substrate-level phosphorylation.

Question 47

Which of the following best describes the regulation of isocitrate dehydrogenase in the TCA cycle? A) Activated by ATP and NADH B) Inhibited by ADP and calcium C) Activated by ADP and calcium D) Inhibited by NAD+ and calcium E) Activated by citrate and succinyl-CoA

Answer 47

Answer: C) Activated by ADP and calcium Explanation: Isocitrate dehydrogenase is allosterically activated by ADP and calcium, signaling low energy states and promoting the TCA cycle.

Question 48

A deficiency in which vitamin would most directly impair the function of α-ketoglutarate dehydrogenase? A) Vitamin B1 (Thiamine) B) Vitamin B2 (Riboflavin) C) Vitamin B3 (Niacin) D) Vitamin B6 (Pyridoxine) E) Vitamin B12 (Cobalamin)

Answer 48

Answer: A) Vitamin B1 (Thiamine) Explanation: Thiamine is a crucial cofactor for α-ketoglutarate dehydrogenase; its deficiency impairs the enzyme's function, affecting the TCA cycle.

Question 49

Which TCA cycle intermediate can be used in gluconeogenesis? A) Citrate B) α-Ketoglutarate C) Succinyl-CoA D) Fumarate E) Malate

Answer 49

Answer: E) Malate Explanation: Malate can be transported out of the mitochondria and converted to oxaloacetate in the cytosol, a substrate for gluconeogenesis.

Question 50

Which of the following statements about the TCA cycle is correct? A) It occurs in the cytosol of the cell B) It directly uses molecular oxygen C) It produces ATP via oxidative phosphorylation D) It generates reducing equivalents for the electron transport chain E) It is primarily regulated by hormonal control

Answer 50

Answer: D) It generates reducing equivalents for the electron transport chain Explanation: The TCA cycle occurs in the mitochondrial matrix and produces NADH and FADH2, which donate electrons to the electron transport chain for ATP production.

Question 51

1. Citrate is diverted from the TCA cycle for fatty acid synthesis under which of the following conditions? A) Low glucose, low energy B) High glucose, low ATP C) High energy state, continued caloric intake D) Low insulin, low NADH

Answer 51

Answer: C) High energy state, continued caloric intake

Question 52

Which intermediate of the TCA cycle is diverted for gluconeogenesis during fasting? A) Citrate B) α-Ketoglutarate C) Oxaloacetate D) Succinyl-CoA

Answer 52

C) Oxaloacetate

Question 52

During high-energy states, what happens to succinyl-CoA? A) Used in ketogenesis B) Shunted to produce heme C) Converted to citrate D) Metabolized to lactate

Answer 52

Answer: B) Shunted to produce heme

Question 53

Which of the following is a correct energy state-to-metabolism match? A) High NAD⁺ → High TCA activity B) High ATP → High ETC activity C) High NADH → High glycolysis D) High ADP → Inhibition of Krebs cycle

Answer 53

A) High NAD⁺ → High TCA activity

Question 54

Which of the following enzymes is embedded in the inner mitochondrial membrane? A) Malate dehydrogenase B) Citrate synthase C) Succinate dehydrogenase D) α-Ketoglutarate dehydrogenase

Answer 54

C) Succinate dehydrogenase

Question 55

A child with congenital lactic acidosis likely has a mutation affecting: A) Lactate dehydrogenase B) Pyruvate kinase C) Pyruvate dehydrogenase D) Isocitrate dehydrogenase

Answer 55

Answer: C) Pyruvate dehydrogenase

Question 55

PDH deficiency most commonly results in accumulation of which metabolite? A) Acetyl-CoA B) Lactate C) Citrate D) GTP

Answer 55

Answer: B) Lactate

Question 56

Arsenic poisoning inhibits which enzymes by binding to lipoic acid? A) Isocitrate and citrate synthase B) PDH and α-Ketoglutarate dehydrogenase C) Succinate dehydrogenase and fumarase D) Aconitase and malate dehydrogenase

Answer 56

Answer: B) PDH and α-Ketoglutarate dehydrogenase

Question 57

What is the rate-limiting enzyme of the TCA cycle? A) Citrate synthase B) Isocitrate dehydrogenase C) Succinate dehydrogenase D) Malate dehydrogenase

Answer 57

Answer: B) Isocitrate dehydrogenase

Question 57

Aconitase is inhibited by: A) Arsenic B) Cyanide C) Fluoroacetate D) Malonate

Answer 57

Answer: C) Fluoroacetate

Question 58

Which of the following is a substrate-level phosphorylation reaction in the TCA cycle? A) Citrate to isocitrate B) Isocitrate to α-ketoglutarate C) Succinyl-CoA to succinate D) Malate to oxaloacetate

Answer 58

Answer: C) Succinyl-CoA to succinate

Question 59

Which of the following is a hallmark feature of arsenic toxicity? A) Cherry red skin B) Mee’s lines on nails C) Blue sclera D) Lens dislocation

Answer 59

Answer: B) Mee’s lines on nails

Question 60

Which of the following is true of oxaloacetate? A) Cannot be used for gluconeogenesis B) Is a ketone body precursor C) Combines with acetyl-CoA to begin the TCA cycle D) Inhibits citrate synthase

Answer 60

C) Combines with acetyl-CoA to begin the TCA cycle

Question 60

What would a high NADH/NAD⁺ ratio indicate? A) Low energy state B) High energy state C) Insulin deficiency D) Hypoxia

Answer 60

B) High energy state

Question 61

A patient in a high-energy state has excess citrate. What secondary pathway is most likely upregulated? A) Gluconeogenesis B) Fatty acid synthesis C) Ketogenesis D) Amino acid catabolism

Answer 61

Answer: B) Fatty acid synthesis

Question 62

In PDH deficiency, why is thiamine given before glucose? A) To increase lactate clearance B) To stimulate ETC activity C) To prevent Wernicke encephalopathy D) To promote insulin release

Answer 62

Answer: C) To prevent Wernicke encephalopathy

Question 63

What vitamin deficiency would most likely lead to impaired function of both PDH and α-KG dehydrogenase? A) Vitamin B12 B) Vitamin B6 C) Vitamin B1 D) Vitamin C

Answer 63

Answer: C) Vitamin B1

Question 64

Which TCA enzyme is inhibited by high levels of ATP and NADH? A) Citrate synthase B) Isocitrate dehydrogenase C) Fumarase D) Malate dehydrogenase

Answer 64

Answer: B) Isocitrate dehydrogenase

Question 65

What condition decreases oxidation of acetyl-CoA in the TCA cycle? A) Low ATP/ADP ratio B) High NADH/NAD⁺ ratio C) Low citrate D) High calcium levels

Answer 65

Answer: B) High NADH/NAD⁺ ratio

Question 66

In the absence of oxygen, which of the following is true? A) TCA cycle runs faster B) ETC is maximally active C) Pyruvate is converted to lactate D) NADH is oxidized in mitochondria

Answer 66

Answer: C) Pyruvate is converted to lactate

Question 67

A patient with CO poisoning presents with confusion and lactic acidosis. Which ETC complex is inhibited? A) Complex I B) Complex II C) Complex III D) Complex IV

Answer 67

Answer: D – CO inhibits Complex IV (cytochrome a3, cytochrome oxidase), preventing electron flow.

Question 68

Rotenone poisoning would most directly lead to accumulation of which molecule? A) ATP B) FADH2 C) NADH D) Ubiquinone

Answer 68

Answer: C – Rotenone blocks Complex I; NADH can’t donate electrons.

Question 69

A researcher mutates succinate dehydrogenase. What is the consequence? A) Glycolysis slows B) NADH levels rise C) Both TCA and ETC are affected D) ATP synthase is overactive

Answer 69

Answer: C – Succinate DH is shared between TCA and Complex II in ETC.

Question 69

Which of the following is NOT required for ATP generation by oxidative phosphorylation? A) Oxygen B) NADH C) ADP D) Pyruvate

Answer 69

Answer: D – Pyruvate feeds upstream in metabolism; not directly needed by ETC.

Question 70

A newborn is diagnosed with mitochondrial disease affecting ATP-ADP translocase. What is expected? A) NADH accumulation B) Cytosolic ATP elevation C) Increased oxygen consumption D) Decreased ATP export to cytoplasm

Answer 70

Answer: D – ATP can’t leave mitochondria without this transporter.

Question 71

Which component of the ETC is lipid-soluble and not a protein? A) Coenzyme Q (Ubiquinone) B) Cytochrome c C) NADH D) Complex III

Answer 71

A) Coenzyme Q (Ubiquinone)

Question 72

Which ETC complex does NOT pump protons across the inner mitochondrial membrane? A) Complex I B) Complex II C) Complex III D) Complex IV

Answer 72

Answer: B – Complex II does not pump H⁺.

Question 73

A 68-year-old man with COPD experiences worsening shortness of breath. Which of the following is most directly impaired in his mitochondria due to chronic hypoxia? A. Flow of electrons through complex II B. Production of NADH in glycolysis C. Phosphorylation of ADP to ATP D. Activity of citrate synthase

Answer 73

Answer: C Why: ETC requires O₂ as the final electron acceptor. Hypoxia = ↓electron flow = ↓ATP.

Question 74

Which of the following conditions most likely leads to metabolic acidosis via electron transport chain impairment? A. Hyperglycemia B. Hypoxia C. High citrate levels D. Low ADP levels

Answer 74

Answer: B Why: Hypoxia → ↓ETC → ↑anaerobic glycolysis → ↑lactic acid → acidosis.

Question 75

Where is the ATP synthase enzyme (complex V) located in the mitochondria? A. Outer membrane B. Cytosol C. Mitochondrial matrix D. Inner mitochondrial membrane

Answer 75

Answer: D Why: All ETC complexes including ATP synthase are in the inner membrane.

Question 76

Which of the following components allows newly synthesized ATP to exit the mitochondrial matrix into the cytoplasm? A. Malate-aspartate shuttle B. Carnitine shuttle C. Nucleotide translocase D. ATP synthase

Answer 76

Answer: C Why: Also called the nucleotide shuttle, it exports ATP out of the mitochondria.

Question 77

What is the direct effect of rotenone poisoning on cellular respiration? A. Inhibition of complex III B. Uncoupling of oxidative phosphorylation C. Blockage of complex I D. Activation of pyruvate kinase

Answer 77

Answer: C Why: Rotenone inhibits complex I, preventing NADH electrons from entering ETC.

Question 78

Which complex of the electron transport chain is not associated with proton pumping? A. Complex I B. Complex II C. Complex III D. Complex IV

Answer 78

Answer: B Why: Complex II does not pump protons. It only transfers FADH₂ electrons.

Question 79

How many ATP molecules are produced per FADH₂ molecule in the electron transport chain? A. 1 B. 2 C. 3 D. 4

Answer 79

Answer: B Why: FADH₂ electrons enter at complex II (skipping I) → 2 ATPs.

Question 80

A patient presents with cyanide poisoning. What complex is most likely inhibited? A. Complex I B. Complex II C. Complex III D. Complex IV

Answer 80

Answer: D Why: Cyanide binds to cytochrome a₃ in complex IV, blocking electron transfer to oxygen.

Question 81

Which of the following best describes the function of uncouplers like 2,4-DNP? A. Inhibit oxygen consumption B. Increase ATP synthesis efficiency C. Transport protons across the inner membrane independently of ATP synthase D. Stimulate NADH production

Answer 81

Answer: C Why: Uncouplers dissipate the proton gradient without producing ATP, generating heat.

Question 82

Which enzyme participates in both the TCA cycle and ETC and is embedded in the inner mitochondrial membrane? A. Aconitase B. Succinate dehydrogenase C. Isocitrate dehydrogenase D. Alpha-ketoglutarate dehydrogenase

Answer 82

Answer: B Why: Succinate dehydrogenase = Complex II, shared by TCA and ETC.

Question 83

What condition would most likely increase activity of the electron transport chain? A. High ATP/ADP ratio B. High citrate levels C. High NADH/NAD⁺ ratio D. High ADP levels

Answer 83

Answer: D Why: High ADP = low energy = ETC ramps up to restore ATP.

Question 84

An experimental drug disrupts the proton gradient across the inner mitochondrial membrane. Which outcome is most likely? A. ↑ NADH oxidation B. ↓ Heat generation C. ↑ ATP synthesis D. ↓ Oxygen consumption

Answer 84

Answer: A Why: Uncoupling → ↑ETC activity (to compensate), ↑O₂ consumption, but no ATP.

Question 85

Which of the following compounds is a key electron donor in the ETC but does not contain a phosphate group? A. ATP B. NADH C. FAD D. GTP

Answer 85

Answer: B Why: NADH does not carry high-energy phosphate bonds; it donates electrons.