2026/2027 Nutrition & Metabolism
Exam Prep
EXAM
1. Q: What is the primary enzyme that initiates starch digestion in
the mouth?
A: Salivary alpha-amylase (ptyalin).
Rationale: It hydrolyzes internal alpha-1,4 glycosidic bonds;
inactivation occurs in the acidic stomach.
2. Q: Which transporter mediates intestinal absorption of
fructose?
A: GLUT5 (facilitative transporter).
Rationale: Unlike glucose and galactose, fructose absorption
does not require SGLT1; GLUT5 is fructose-specific.
3. Q: Name the enzyme responsible for digesting triglycerides
into 2-monoacylglycerol and free fatty acids in the small intestine.
A: Pancreatic lipase.
Rationale: It requires colipase and bile salts; its optimal pH is ~6–
7.
4. Q: What is the role of chylomicrons in lipid metabolism?
A: Transport dietary (exogenous) triglycerides and cholesterol
from enterocytes to peripheral tissues via lymph and blood.
Rationale: Chylomicrons are the largest lipoproteins; they are
formed in the small intestine.
,5. Q: Which gastric cell secretes intrinsic factor, and why is it
essential?
A: Parietal cells; intrinsic factor binds vitamin B₁₂, enabling its
absorption in the terminal ileum.
Rationale: Without intrinsic factor, pernicious anemia develops
due to B₁₂ deficiency.
Carbohydrate Metabolism
6. Q: What is the net ATP yield from glycolysis per molecule of
glucose?
A: 2 ATP (substrate-level phosphorylation) + 2 NADH.
Rationale: 4 ATP produced, 2 consumed; NADH yield varies with
shuttle system.
7. Q: Name the rate-limiting enzyme of glycolysis in most tissues.
A: Phosphofructokinase-1 (PFK-1).
Rationale: Allosterically activated by
AMP/fructose-2,6-bisphosphate, inhibited by ATP/citrate.
8. Q: Under anaerobic conditions, how is NAD⁺ regenerated in
muscle?
A: Lactate dehydrogenase converts pyruvate to lactate.
Rationale: This allows glycolysis to continue without oxygen;
lactate is later recycled via Cori cycle.
9. Q: What is the primary gluconeogenic precursor released from
muscle during fasting?
A: Alanine (via glucose-alanine cycle).
, Rationale: Muscle degrades branched-chain amino acids,
transferring nitrogen to pyruvate forming alanine.
10. Q: Which enzyme is unique to gluconeogenesis, bypassing the
irreversible pyruvate kinase step?
A: Pyruvate carboxylase (mitochondrial) plus
phosphoenolpyruvate carboxykinase (PEPCK).
Rationale: They convert pyruvate → oxaloacetate →
phosphoenolpyruvate.
11. Q: What is the major hormonal activator of gluconeogenesis
during fasting?
A: Glucagon.
Rationale: Glucagon lowers fructose-2,6-bisphosphate, inhibiting
glycolysis and activating gluconeogenesis.
12. Q: Which vitamin is a cofactor for pyruvate dehydrogenase
complex (PDH)?
A: Thiamine (B₁) as thiamine pyrophosphate (TPP).
Rationale: TPP is required for the decarboxylation step; deficiency
impairs aerobic glucose oxidation.
Lipid Metabolism
13. Q: Where does beta-oxidation of fatty acids occur?
A: Mitochondrial matrix (for short-, medium-, long-chain;
very-long-chain starts in peroxisomes).
Rationale: Carnitine shuttle transports long-chain acyl-CoA across
inner mitochondrial membrane.
Exam Prep
EXAM
1. Q: What is the primary enzyme that initiates starch digestion in
the mouth?
A: Salivary alpha-amylase (ptyalin).
Rationale: It hydrolyzes internal alpha-1,4 glycosidic bonds;
inactivation occurs in the acidic stomach.
2. Q: Which transporter mediates intestinal absorption of
fructose?
A: GLUT5 (facilitative transporter).
Rationale: Unlike glucose and galactose, fructose absorption
does not require SGLT1; GLUT5 is fructose-specific.
3. Q: Name the enzyme responsible for digesting triglycerides
into 2-monoacylglycerol and free fatty acids in the small intestine.
A: Pancreatic lipase.
Rationale: It requires colipase and bile salts; its optimal pH is ~6–
7.
4. Q: What is the role of chylomicrons in lipid metabolism?
A: Transport dietary (exogenous) triglycerides and cholesterol
from enterocytes to peripheral tissues via lymph and blood.
Rationale: Chylomicrons are the largest lipoproteins; they are
formed in the small intestine.
,5. Q: Which gastric cell secretes intrinsic factor, and why is it
essential?
A: Parietal cells; intrinsic factor binds vitamin B₁₂, enabling its
absorption in the terminal ileum.
Rationale: Without intrinsic factor, pernicious anemia develops
due to B₁₂ deficiency.
Carbohydrate Metabolism
6. Q: What is the net ATP yield from glycolysis per molecule of
glucose?
A: 2 ATP (substrate-level phosphorylation) + 2 NADH.
Rationale: 4 ATP produced, 2 consumed; NADH yield varies with
shuttle system.
7. Q: Name the rate-limiting enzyme of glycolysis in most tissues.
A: Phosphofructokinase-1 (PFK-1).
Rationale: Allosterically activated by
AMP/fructose-2,6-bisphosphate, inhibited by ATP/citrate.
8. Q: Under anaerobic conditions, how is NAD⁺ regenerated in
muscle?
A: Lactate dehydrogenase converts pyruvate to lactate.
Rationale: This allows glycolysis to continue without oxygen;
lactate is later recycled via Cori cycle.
9. Q: What is the primary gluconeogenic precursor released from
muscle during fasting?
A: Alanine (via glucose-alanine cycle).
, Rationale: Muscle degrades branched-chain amino acids,
transferring nitrogen to pyruvate forming alanine.
10. Q: Which enzyme is unique to gluconeogenesis, bypassing the
irreversible pyruvate kinase step?
A: Pyruvate carboxylase (mitochondrial) plus
phosphoenolpyruvate carboxykinase (PEPCK).
Rationale: They convert pyruvate → oxaloacetate →
phosphoenolpyruvate.
11. Q: What is the major hormonal activator of gluconeogenesis
during fasting?
A: Glucagon.
Rationale: Glucagon lowers fructose-2,6-bisphosphate, inhibiting
glycolysis and activating gluconeogenesis.
12. Q: Which vitamin is a cofactor for pyruvate dehydrogenase
complex (PDH)?
A: Thiamine (B₁) as thiamine pyrophosphate (TPP).
Rationale: TPP is required for the decarboxylation step; deficiency
impairs aerobic glucose oxidation.
Lipid Metabolism
13. Q: Where does beta-oxidation of fatty acids occur?
A: Mitochondrial matrix (for short-, medium-, long-chain;
very-long-chain starts in peroxisomes).
Rationale: Carnitine shuttle transports long-chain acyl-CoA across
inner mitochondrial membrane.
