UNIVERSITY OF NEW ENGLAND MBS 650
BIOCHEMICAL PATHWAYS EXAM 2026
WITH 100% ACCURATE QUESTIONS 7
ANSWERS
1. Describe the role of carbamoyl phosphate synthetase I in the urea cycle.
Carbamoyl phosphate synthetase I initiates the urea cycle by
converting ammonia and bicarbonate into carbamoyl
phosphate.
Carbamoyl phosphate synthetase I regulates the synthesis of
nucleotides.
Carbamoyl phosphate synthetase I is involved in lipid metabolism.
Carbamoyl phosphate synthetase I catalyzes the conversion of
urea into ammonia.
2. Describe the role of tetrahydrobiopterin (BH4) in the metabolism of
phenylalanine.
Tetrahydrobiopterin (BH4) acts as a cofactor for the enzyme
that converts phenylalanine to tyrosine.
Tetrahydrobiopterin (BH4) is involved in the synthesis of
nucleotides.
Tetrahydrobiopterin (BH4) regulates insulin levels in the body.
Tetrahydrobiopterin (BH4) is necessary for cholesterol synthesis.
3. Which one of the following biochemical species is a "ketone body"
whose levels are elevated in diabetic ketoacidosis?
Pyruvate
Citrate
,Oxaloacetate
Acetate
, Beta-hydroxybutyrate
4. Describe the role of xanthine oxidase in purine metabolism and how its
inhibition by allopurinol helps manage gout symptoms.
Xanthine oxidase is responsible for the detoxification of
ammonia; inhibiting it leads to increased ammonia levels.
Xanthine oxidase converts nucleotides into amino acids;
inhibiting it prevents amino acid synthesis.
Xanthine oxidase is involved in cholesterol synthesis; inhibiting it
lowers cholesterol levels.
Xanthine oxidase catalyzes the conversion of hypoxanthine to
xanthine and xanthine to uric acid; inhibiting it reduces uric
acid production, alleviating gout symptoms.
5. If a patient has a folate deficiency, which nucleotide synthesis would be
least affected based on the information provided?
ATP
CTP
GTP
UTP
6. A comatose infant is brought to the ER. Plasma ammonia is found to be
elevated. Urine orotic acid and uracil were both greater then normal.
Which enzyme is deficient?
Carbamoyl Phosphate synthetase I
N-acetylglutamate synthetase
Ornithine transcarbamoylase
Carbamoyl phosphate synthetase II
, PRPP synthetase
7. Which compound is essential for converting phenylalanine into
tyrosine?
Phenylalanine
Tryptophan
tetrahydrofolate (THF)
tetrahydrobiopterin (BH4)
8. If a patient has a deficiency in HGPRT, what metabolic consequence
might they experience related to purine metabolism?
Enhanced degradation of purines resulting in lower uric acid
levels.
Decreased synthesis of nucleotides leading to reduced DNA
replication.
Increased conversion of AMP to ATP, causing energy surplus.
Accumulation of uric acid due to impaired purine salvage.
9. Describe the significance of the carboxylation of acetyl-CoA in the
process of lipogenesis.
The carboxylation of acetyl-CoA is significant because it
generates ATP for energy production.
The carboxylation of acetyl-CoA is significant because it
synthesizes cholesterol.
The carboxylation of acetyl-CoA is significant because it leads to
the breakdown of fatty acids.
The carboxylation of acetyl-CoA is significant because it
converts acetyl-CoA into malonyl-CoA, which is a key
precursor for fatty acid synthesis.
BIOCHEMICAL PATHWAYS EXAM 2026
WITH 100% ACCURATE QUESTIONS 7
ANSWERS
1. Describe the role of carbamoyl phosphate synthetase I in the urea cycle.
Carbamoyl phosphate synthetase I initiates the urea cycle by
converting ammonia and bicarbonate into carbamoyl
phosphate.
Carbamoyl phosphate synthetase I regulates the synthesis of
nucleotides.
Carbamoyl phosphate synthetase I is involved in lipid metabolism.
Carbamoyl phosphate synthetase I catalyzes the conversion of
urea into ammonia.
2. Describe the role of tetrahydrobiopterin (BH4) in the metabolism of
phenylalanine.
Tetrahydrobiopterin (BH4) acts as a cofactor for the enzyme
that converts phenylalanine to tyrosine.
Tetrahydrobiopterin (BH4) is involved in the synthesis of
nucleotides.
Tetrahydrobiopterin (BH4) regulates insulin levels in the body.
Tetrahydrobiopterin (BH4) is necessary for cholesterol synthesis.
3. Which one of the following biochemical species is a "ketone body"
whose levels are elevated in diabetic ketoacidosis?
Pyruvate
Citrate
,Oxaloacetate
Acetate
, Beta-hydroxybutyrate
4. Describe the role of xanthine oxidase in purine metabolism and how its
inhibition by allopurinol helps manage gout symptoms.
Xanthine oxidase is responsible for the detoxification of
ammonia; inhibiting it leads to increased ammonia levels.
Xanthine oxidase converts nucleotides into amino acids;
inhibiting it prevents amino acid synthesis.
Xanthine oxidase is involved in cholesterol synthesis; inhibiting it
lowers cholesterol levels.
Xanthine oxidase catalyzes the conversion of hypoxanthine to
xanthine and xanthine to uric acid; inhibiting it reduces uric
acid production, alleviating gout symptoms.
5. If a patient has a folate deficiency, which nucleotide synthesis would be
least affected based on the information provided?
ATP
CTP
GTP
UTP
6. A comatose infant is brought to the ER. Plasma ammonia is found to be
elevated. Urine orotic acid and uracil were both greater then normal.
Which enzyme is deficient?
Carbamoyl Phosphate synthetase I
N-acetylglutamate synthetase
Ornithine transcarbamoylase
Carbamoyl phosphate synthetase II
, PRPP synthetase
7. Which compound is essential for converting phenylalanine into
tyrosine?
Phenylalanine
Tryptophan
tetrahydrofolate (THF)
tetrahydrobiopterin (BH4)
8. If a patient has a deficiency in HGPRT, what metabolic consequence
might they experience related to purine metabolism?
Enhanced degradation of purines resulting in lower uric acid
levels.
Decreased synthesis of nucleotides leading to reduced DNA
replication.
Increased conversion of AMP to ATP, causing energy surplus.
Accumulation of uric acid due to impaired purine salvage.
9. Describe the significance of the carboxylation of acetyl-CoA in the
process of lipogenesis.
The carboxylation of acetyl-CoA is significant because it
generates ATP for energy production.
The carboxylation of acetyl-CoA is significant because it
synthesizes cholesterol.
The carboxylation of acetyl-CoA is significant because it leads to
the breakdown of fatty acids.
The carboxylation of acetyl-CoA is significant because it
converts acetyl-CoA into malonyl-CoA, which is a key
precursor for fatty acid synthesis.
