, CHEM 212 MODULE 8 EXAM
Biochemistry w/Lab
Portage Learning
100-Question Practice Examination
2026/2027 Edition
CHEM 212 Module 8 Exam | Biochemistry w/Lab | Portage Learning | Q & A | 2026/2027 Actual
(PDF)
1. During amino acid catabolism, which reaction most commonly transfers an amino group to alpha-
ketoglutarate?
A) Decarboxylation
B) Beta oxidation
C) Transamination
D) Substrate-level phosphorylation
Correct Answer: Transamination
Rationale: Transamination transfers an amino group from an amino acid to an alpha-keto acid, commonly alpha-
ketoglutarate, producing glutamate. This channels nitrogen toward safe disposal. Beta oxidation degrades fatty acids,
decarboxylation removes carbon dioxide, and substrate-level phosphorylation directly forms ATP.
2. Which molecule serves as a major collection point for amino nitrogen before ammonia is released for urea
synthesis?
A) Acetyl-CoA
B) Citrate
C) Pyruvate
D) Glutamate
Correct Answer: Glutamate
Rationale: Glutamate accepts amino groups from many amino acids through aminotransferase reactions. Oxidative
deamination of glutamate can then release ammonium for nitrogen disposal. Pyruvate, citrate, and acetyl-CoA are
important carbon-metabolism intermediates but are not the principal nitrogen collection molecule.
3. Oxidative deamination of glutamate directly produces ammonium and which carbon skeleton?
A) Acetoacetate
B) Alpha-ketoglutarate
C) Oxaloacetate
D) Succinate
Correct Answer: Alpha-ketoglutarate
Rationale: Glutamate dehydrogenase converts glutamate to alpha-ketoglutarate while releasing ammonium. The alpha-
ketoglutarate can re-enter the citric acid cycle, linking nitrogen removal to energy metabolism. Oxaloacetate, succinate,
and acetoacetate are not the direct carbon products of this reaction.
4. Which compound safely transports excess nitrogen from many peripheral tissues to the liver?
A) Creatine
B) Urea
C) Bicarbonate
D) Glutamine
CHEM 212 Module 8 Practice Examination | 2026/2027 | Page 1
, Correct Answer: Glutamine
Rationale: Glutamine synthetase incorporates free ammonium into glutamate to form glutamine, a nontoxic nitrogen
carrier. In the liver, glutaminase can release the nitrogen for urea synthesis. Urea is mainly an excretory product rather
than the major peripheral transport form.
5. In skeletal muscle, nitrogen can be transported to the liver as alanine through the glucose-alanine cycle. Which
metabolite accepts the amino group to form alanine?
A) Pyruvate
B) Citrate
C) Acetyl-CoA
D) Lactate
Correct Answer: Pyruvate
Rationale: Alanine aminotransferase transfers an amino group from glutamate to pyruvate, producing alanine and alpha-
ketoglutarate. Alanine travels to the liver, where its nitrogen can enter urea synthesis and its carbon skeleton can support
gluconeogenesis.
6. Why is free ammonia especially dangerous at high concentrations?
A) It irreversibly hydrolyzes ATP in plasma
B) It disrupts cellular and especially brain metabolism
C) It directly polymerizes DNA
D) It converts all fatty acids to ketones
Correct Answer: It disrupts cellular and especially brain metabolism
Rationale: Ammonia is neurotoxic and can disturb acid-base balance and central metabolic pathways, including depletion
of key intermediates through glutamate and glutamine formation. The other choices describe processes that do not
represent the principal biochemical toxicity of ammonia.
7. The urea cycle primarily converts toxic nitrogen into which water-soluble excretory product?
A) Urea
B) Creatinine
C) Ammonium chloride
D) Uric acid
Correct Answer: Urea
Rationale: In humans, the urea cycle converts nitrogen derived largely from ammonia and aspartate into urea. Urea is
relatively nontoxic and water soluble, allowing efficient renal excretion. Uric acid and creatinine arise from different
metabolic pathways.
8. Where does the first committed reaction of the urea cycle occur?
A) Nuclear matrix
B) Mitochondrial matrix
C) Endoplasmic reticulum lumen
D) Cytosol
Correct Answer: Mitochondrial matrix
Rationale: Carbamoyl phosphate synthetase I is located in the mitochondrial matrix and initiates urea-cycle nitrogen
incorporation. Later reactions occur mostly in the cytosol, so compartmentalization is an essential feature of the pathway.
9. Which enzyme forms carbamoyl phosphate from ammonium, bicarbonate, and ATP in the urea cycle?
A) Carbamoyl phosphate synthetase I
B) Arginase
CHEM 212 Module 8 Practice Examination | 2026/2027 | Page 2
Biochemistry w/Lab
Portage Learning
100-Question Practice Examination
2026/2027 Edition
CHEM 212 Module 8 Exam | Biochemistry w/Lab | Portage Learning | Q & A | 2026/2027 Actual
(PDF)
1. During amino acid catabolism, which reaction most commonly transfers an amino group to alpha-
ketoglutarate?
A) Decarboxylation
B) Beta oxidation
C) Transamination
D) Substrate-level phosphorylation
Correct Answer: Transamination
Rationale: Transamination transfers an amino group from an amino acid to an alpha-keto acid, commonly alpha-
ketoglutarate, producing glutamate. This channels nitrogen toward safe disposal. Beta oxidation degrades fatty acids,
decarboxylation removes carbon dioxide, and substrate-level phosphorylation directly forms ATP.
2. Which molecule serves as a major collection point for amino nitrogen before ammonia is released for urea
synthesis?
A) Acetyl-CoA
B) Citrate
C) Pyruvate
D) Glutamate
Correct Answer: Glutamate
Rationale: Glutamate accepts amino groups from many amino acids through aminotransferase reactions. Oxidative
deamination of glutamate can then release ammonium for nitrogen disposal. Pyruvate, citrate, and acetyl-CoA are
important carbon-metabolism intermediates but are not the principal nitrogen collection molecule.
3. Oxidative deamination of glutamate directly produces ammonium and which carbon skeleton?
A) Acetoacetate
B) Alpha-ketoglutarate
C) Oxaloacetate
D) Succinate
Correct Answer: Alpha-ketoglutarate
Rationale: Glutamate dehydrogenase converts glutamate to alpha-ketoglutarate while releasing ammonium. The alpha-
ketoglutarate can re-enter the citric acid cycle, linking nitrogen removal to energy metabolism. Oxaloacetate, succinate,
and acetoacetate are not the direct carbon products of this reaction.
4. Which compound safely transports excess nitrogen from many peripheral tissues to the liver?
A) Creatine
B) Urea
C) Bicarbonate
D) Glutamine
CHEM 212 Module 8 Practice Examination | 2026/2027 | Page 1
, Correct Answer: Glutamine
Rationale: Glutamine synthetase incorporates free ammonium into glutamate to form glutamine, a nontoxic nitrogen
carrier. In the liver, glutaminase can release the nitrogen for urea synthesis. Urea is mainly an excretory product rather
than the major peripheral transport form.
5. In skeletal muscle, nitrogen can be transported to the liver as alanine through the glucose-alanine cycle. Which
metabolite accepts the amino group to form alanine?
A) Pyruvate
B) Citrate
C) Acetyl-CoA
D) Lactate
Correct Answer: Pyruvate
Rationale: Alanine aminotransferase transfers an amino group from glutamate to pyruvate, producing alanine and alpha-
ketoglutarate. Alanine travels to the liver, where its nitrogen can enter urea synthesis and its carbon skeleton can support
gluconeogenesis.
6. Why is free ammonia especially dangerous at high concentrations?
A) It irreversibly hydrolyzes ATP in plasma
B) It disrupts cellular and especially brain metabolism
C) It directly polymerizes DNA
D) It converts all fatty acids to ketones
Correct Answer: It disrupts cellular and especially brain metabolism
Rationale: Ammonia is neurotoxic and can disturb acid-base balance and central metabolic pathways, including depletion
of key intermediates through glutamate and glutamine formation. The other choices describe processes that do not
represent the principal biochemical toxicity of ammonia.
7. The urea cycle primarily converts toxic nitrogen into which water-soluble excretory product?
A) Urea
B) Creatinine
C) Ammonium chloride
D) Uric acid
Correct Answer: Urea
Rationale: In humans, the urea cycle converts nitrogen derived largely from ammonia and aspartate into urea. Urea is
relatively nontoxic and water soluble, allowing efficient renal excretion. Uric acid and creatinine arise from different
metabolic pathways.
8. Where does the first committed reaction of the urea cycle occur?
A) Nuclear matrix
B) Mitochondrial matrix
C) Endoplasmic reticulum lumen
D) Cytosol
Correct Answer: Mitochondrial matrix
Rationale: Carbamoyl phosphate synthetase I is located in the mitochondrial matrix and initiates urea-cycle nitrogen
incorporation. Later reactions occur mostly in the cytosol, so compartmentalization is an essential feature of the pathway.
9. Which enzyme forms carbamoyl phosphate from ammonium, bicarbonate, and ATP in the urea cycle?
A) Carbamoyl phosphate synthetase I
B) Arginase
CHEM 212 Module 8 Practice Examination | 2026/2027 | Page 2
