FINAL METABOLIC PATHWAYS

Question 1

A red blood cell relies almost entirely on which pathway for ATP production?

A. Krebs cycle
B. Oxidative phosphorylation
C. Glycolysis
D. β-oxidation

Answer 1

C
RBCs lack mitochondria → glycolysis is the ONLY ATP source.

Question 2

A patient with pyruvate kinase deficiency is most likely to develop which condition?

A. Megaloblastic anemia
B. Hemolytic anemia
C. Iron deficiency anemia
D. Aplastic anemia

Answer 2

B

Question 3

Which glycolytic enzyme is the rate-limiting step and most heavily regulated?

A. Hexokinase
B. Aldolase
C. Phosphofructokinase-1
D. Enolase

Answer 3

C

Question 4

A patient exercising intensely develops muscle fatigue due to ATP depletion. Which enzyme deficiency is MOST likely?

A. Hexokinase
B. PFK-1
C. Pyruvate carboxylase
D. Citrate synthase

Answer 4

B

Question 5

Fluoride is added to blood collection tubes to inhibit which glycolytic enzyme?

A. Aldolase
B. Enolase
C. Pyruvate kinase
D. Triose phosphate isomerase

Answer 5

B

Question 6

Which tissue depends MOST on glycolysis during hypoxia?

A. Liver
B. Brain
C. Red blood cells
D. Adipose tissue

Answer 6

C

Question 7

During anaerobic glycolysis, pyruvate is converted to lactate primarily to:

A. Generate ATP
B. Enter the TCA cycle
C. Regenerate NAD⁺
D. Remove CO₂

Answer 7

C

Question 8

A child presents with jaundice, elevated indirect bilirubin, and reticulocytosis. RBC enzyme assay shows ↓ pyruvate kinase. Why are RBCs especially affected?

A. They require oxidative phosphorylation
B. They lack nuclei
C. They lack mitochondria
D. They cannot store glucose

Answer 8

C

Question 9

Which organ maintains blood glucose during fasting?

A. Muscle
B. Liver
C. Brain
D. Kidney medulla

Answer 9

B

Question 10

A child develops muscle cramps and dark urine after exercise. Blood glucose is normal. Diagnosis?

A. Von Gierke disease
B. Pompe disease
C. McArdle disease
D. Cori disease

Answer 10

C
Explanation: McArdle = muscle glycogen phosphorylase deficiency.

Question 12

Why is blood glucose normal in McArdle disease?

A. Increased gluconeogenesis
B. Liver glycogen metabolism is normal
C. Muscle releases glucose
D. Increased insulin

Answer 12

B

Question 13

The rate-limiting enzyme of glycogen synthesis is:

A. Glycogen phosphorylase
B. Debranching enzyme
C. Glycogen synthase
D. Hexokinase

Answer 13

C

Question 14

Glycogen phosphorylase is most active when:

A. Dephosphorylated
B. Bound to insulin
C. Phosphorylated
D. ATP levels are high

Answer 14

C

Question 15

Which hormone stimulates glycogen breakdown in muscle?

A. Insulin
B. Cortisol
C. Glucagon
D. Epinephrine

Answer 15

D

Question 16

Which substrate contributes to gluconeogenesis during anaerobic exercise?

A. Acetyl-CoA
B. Lactate
C. Fatty acids
D. Ketone bodies

Answer 16

B
Cori cycle

Question 17

Which enzyme is ABSENT in muscle, preventing glucose export?

A. Hexokinase
B. PEPCK
C. Glucose-6-phosphatase
D. Aldolase

Answer 17

C

Question 18

A fasting child develops hypoglycemia and lactic acidosis. Which enzyme is most likely deficient?

A. PFK-1
B. Pyruvate kinase
C. Glucose-6-phosphatase
D. Enolase

Answer 18

C
Von Gierke disease

Question 19

Which hormone primarily stimulates gluconeogenesis?

A. Insulin
B. Glucagon
C. Growth hormone
D. Thyroxine

Answer 19

B

Question 20

Pyruvate dehydrogenase converts pyruvate into:

A. Lactate
B. Acetyl-CoA
C. Oxaloacetate
D. Alanine

Answer 20

B

Question 21

Thiamine deficiency most directly impairs which process?

A. Glycolysis
B. PDH activity
C. β-oxidation
D. Glycogen synthesis

Answer 21

B

Question 22

A child with lactic acidosis and neurologic defects likely has deficiency of:

A. Citrate synthase
B. Pyruvate dehydrogenase
C. Succinate dehydrogenase
D. Malate dehydrogenase

Answer 22

B

Question 23

A fasting infant presents with hypoglycemia and low ketones. Likely diagnosis?

A. PKU
B. MCAD deficiency
C. Von Gierke disease
D. McArdle disease

Answer 23

B

Question 24

Why is hypoketotic hypoglycemia seen in MCAD deficiency?

A. Excess insulin
B. Impaired ketone synthesis
C. Excess lactate
D. Increased glycolysis

Answer 24

B

Question 25

Which compound is required to transport long-chain fatty acids into mitochondria? A. Biotin B. Carnitine C. Coenzyme A D. NAD⁺

Answer 25

B

Question 26

A child from the Caribbean develops vomiting and hypoglycemia after eating unripe ackee fruit. Mechanism? A. Inhibition of PDH B. Inhibition of β-oxidation C. Increased insulin release D. Decreased gluconeogenesis enzymes

Answer 26

B

Question 27

5-year-old child presents with fatigue and jaundice. Labs show reticulocytosis and elevated indirect bilirubin. RBC enzyme assay shows ↓ pyruvate kinase. Which step of glycolysis is directly impaired? A. Glucose → Glucose-6-phosphate B. Fructose-6-phosphate → Fructose-1,6-bisphosphate C. Phosphoenolpyruvate → Pyruvate D. Glyceraldehyde-3-phosphate → 1,3-BPG

Answer 27

C

Question 28

Why does pyruvate kinase deficiency cause hemolytic anemia? A. Accumulation of pyruvate B. Reduced NADH production C. ATP depletion in RBCs D. Increased lactate production

Answer 28

C

Question 29

In pyruvate kinase deficiency, increased 2,3-BPG causes which effect? A. Left shift of O₂ dissociation curve B. Right shift of O₂ dissociation curve C. Increased hemoglobin affinity for O₂ D. Reduced oxygen delivery

Answer 29

B

Question 30

A 7-year-old boy develops muscle pain and dark urine after soccer. CK and myoglobin are elevated. Blood glucose is normal. Most likely diagnosis? A. Von Gierke disease B. Pompe disease C. McArdle disease D. Cori disease

Answer 30

C

Question 31

The enzyme deficient in McArdle disease is: A. Liver glycogen phosphorylase B. Muscle glycogen phosphorylase C. Debranching enzyme D. Glycogen synthase

Answer 31

B

Question 32

Why does the “second wind phenomenon” occur in McArdle disease? A. Increased glycogen breakdown B. Switch to fatty acid oxidation C. Increased blood glucose delivery D. Increased lactate clearance

Answer 32

C

Question 33

What serious complication can occur if exercise continues in McArdle disease? A. Hypoglycemia B. Rhabdomyolysis C. Ketoacidosis D. Liver failure

Answer 33

B

Question 34

A 4-year-old becomes lethargic after overnight fasting. Labs show hypoglycemia, lactic acidosis, and hepatomegaly. Most likely enzyme deficiency? A. Pyruvate kinase B. PEPCK C. Glucose-6-phosphatase D. Hexokinase

Answer 34

C Explanation: Classic Von Gierke disease.

Question 35

Why does glucose-6-phosphatase deficiency cause lactic acidosis? A. Increased pyruvate oxidation B. Impaired glycolysis C. Accumulated G6P shunted to glycolysis D. Increased β-oxidation

Answer 35

C

Question 36

Which tissue lacks glucose-6-phosphatase and therefore cannot release glucose? A. Liver B. Kidney C. Muscle D. Intestine

Answer 36

C

Question 37

A child presents with lactic acidosis, ↑ alanine, and neurologic deficits after high-carbohydrate meals. Which enzyme complex is deficient? A. Isocitrate dehydrogenase B. Pyruvate dehydrogenase C. Succinate dehydrogenase D. Citrate synthase

Answer 37

B

Question 38

Pyruvate dehydrogenase deficiency causes accumulation of: A. Acetyl-CoA B. Lactate C. CO₂ D. FADH₂

Answer 38

B

Question 39

Which cofactor deficiency produces symptoms similar to PDH deficiency? A. Riboflavin B. Niacin C. Thiamine D. Biotin

Answer 39

C

Question 40

A 9-month-old infant presents with lethargy and seizures after fasting. Labs show hypoglycemia, low ketones, and dicarboxylic aciduria. Diagnosis? A. CPT-I deficiency B. MCAD deficiency C. PKU D. Von Gierke disease

Answer 40

B

Question 41

Why are ketone bodies low in MCAD deficiency? A. Excess insulin B. Impaired acetyl-CoA formation C. Increased gluconeogenesis D. Decreased fatty acid release

Answer 41

B

Question 42

Unmetabolized fatty acids in MCAD deficiency are diverted into which pathway? A. Glycolysis B. TCA cycle C. ω-oxidation D. Ketogenesis

Answer 42

C

Question 43

Unripe ackee fruit causes toxicity by inhibiting: A. Carnitine transport B. Acyl-CoA dehydrogenase C. Pyruvate carboxylase D. Glycogen phosphorylase

Answer 43

B

Question 44

Biochemical pattern of ackee fruit poisoning resembles: A. PKU B. PDH deficiency C. MCAD deficiency D. Von Gierke disease

Answer 44

C

Question 45

A newborn has sweet-smelling urine and neurologic symptoms. Deficient enzyme? A. Phenylalanine hydroxylase B. Branched-chain α-ketoacid dehydrogenase C. Tyrosinase D. Arginase

Answer 45

B

Question 46

Which amino acids accumulate in MSUD? A. Alanine, glycine, serine B. Leucine, isoleucine, valine C. Phenylalanine, tyrosine D. Aspartate, glutamate

Answer 46

B

Question 47

A baby has musty-smelling urine, hypopigmented skin, and seizures. Diagnosis? A. MSUD B. Alkaptonuria C. PKU D. Tyrosinemia

Answer 47

C

Question 48

Why do PKU patients have light skin and hair? A. Low melanin due to ↓ tyrosine B. Decreased iron absorption C. Reduced ATP production D. Increased phenylalanine breakdown

Answer 48

A

Question 49

A factory worker collapses after inhaling smoke from burning plastics. O₂ saturation is normal but lactate is high. Diagnosis? A. Carbon monoxide poisoning B. Cyanide poisoning C. Methemoglobinemia D. Arsenic poisoning

Answer 49

B

Question 50

Cyanide causes toxicity by inhibiting which ETC complex? A. Complex I B. Complex II C. Complex III D. Complex IV

Answer 50

D

Question 51

Why is oxygen therapy ineffective in cyanide poisoning? A. O₂ cannot bind hemoglobin B. ETC cannot utilize oxygen C. Oxygen delivery is impaired D. Mitochondria are absent

Answer 51

B

Question 52

Which pathway is the primary source of ATP in red blood cells? A. TCA cycle B. Oxidative phosphorylation C. Glycolysis D. β-oxidation

Answer 52

C

Question 53

Which glycolytic enzyme “traps” glucose inside the cell? A. PFK-1 B. Hexokinase C. Aldolase D. Enolase

Answer 53

B

Question 54

Glucokinase differs from hexokinase because glucokinase: A. Is inhibited by glucose-6-phosphate B. Has high affinity for glucose C. Functions as a glucose sensor D. Is present in muscle

Answer 54

C

Question 55

Which molecule inhibits PFK-1, slowing glycolysis? A. AMP B. Fructose-2,6-bisphosphate C. ATP D. ADP

Answer 55

C

Question 56

PFK-1 deficiency most directly causes: A. Hypoglycemia B. Exercise intolerance C. Hyperketonemia D. Fatty liver

Answer 56

B

Question 57

Which step of glycolysis produces NADH? A. Glucose → G6P B. F6P → F1,6BP C. G3P → 1,3-BPG D. PEP → Pyruvate

Answer 57

C

Question 58

Substrate-level phosphorylation occurs in glycolysis at which steps? A. Steps 1 and 3 B. Steps 6 and 7 C. Steps 7 and 10 D. Steps 8 and 9

Answer 58

C

Question 59

Which enzyme is inhibited by fluoride in blood collection tubes? A. Pyruvate kinase B. Enolase C. Aldolase D. Hexokinase

Answer 59

B