Biochemistry Final Exam 3 Questions
with Guaranteed Pass Solutions 2025-
2026 Updated.
The conversion of ribose-1-phosphate to guanosine-5'-triphosphate via the salvage pathway
would require the activity of several enzymes. Choose the answer that lists them in the order
that they would act in this pathway.
A. PRPP synthetase; phosphopentomutase; kinase; kinase; phosphoriboxyl transferase
B. phosphopentomutase; phosphoriboxyl transferase; kinase; PRPP synthetase; kinase
C. PRPP synthetase; phosphoriboxyl transferase; phosphopentomutase; kinase; kinase
D. phosphopentomutase; PRPP synthetase; phosphoriboxyl transferase; kinase; kinase - Answer
D. phosphopentomutase; PRPP synthetase; phosphoriboxyl transferase; kinase; kinase
What molecule signals the endothelial cell to produce nitric oxide, and what is the enzymatic
reaction? - Answer acetylcholine
L-arginine + 1.5 NADP+ + H+ + 2O2 --> citrulline + NO + 1.5 NADPH
Diseases affecting heme biosynthesis as a result of deficiencies in the heme biosynthetic
pathway are called _________.
a. phenylketonuria
b. albinism
c. porphyria
d. alkaptonuria - Answer c. porphyria
What is the mechanism by which glyphosate, the active ingredient in Roundup, kills plants? -
Answer Glyphosate is a competitive inhibitor of plant EPSP synthase
Aspartate is a(n) ________ amino acid, so if a person had a diet that contained no aspartate
then ________.
a. nonessential; they would be unable to synthesize proteins
b. essential; they would be unable to synthesize proteins
c. essential; aspartate could be synthesized from other intermediates
,A person who has alkaptonuria is easily diagnosed from their black urine. What causes the black
color?
a. phenylpyruvate and phenylacetate
b. oxidation of phenylalanine
c. oxidation of homogentisate
d. reduction of acetoacetyl-CoA - Answer c. oxidation of homogentisate
What is the regulatory mechanism by which arginine stimulates flux thru the urea cycle?
A. Arginine stimulates flux through the urea cycle by inhibiting the enzyme nitrogenase.
B. Arginine stimulates the production of N-acetylglutamate which activates arginase.
C. Arginine stimulates the production of the allosteric activator N-acetylglutamate.
D. Arginine stimulates the activity of carbamoyl phosphate synthetase I. - Answer C. Arginine
stimulates the production of the allosteric activator N-acetylglutamate.
Which of the three proteins in the ubiquination pathway is the most responsible for recognizing
the ubiquintated target protein?
a. E2
b. E3
c. E1
d. all 3 of the proteins recognize the target protein - Answer b. E3
In the duodenum, enteropeptidase _.
a. neutralizes the pH of the duodenum to a pH of 7
b. cleaves chymotripsinogen to form chymotrypsin
c. generates peptides and amino acids
d. cleaves trypsinogen to form trypsin - Answer d. cleaves trypsinogen to form trypsin
How is protein ubiquitination regulated? - Answer 2 common mechanisms:
1. biochemical changes in target proteins
such as N-terminal cleavage or phosphorylation
2. biochemical changes in E3 ligases
,What is the net reaction of the urea cycle? - Answer NH4 + + HCO3 − + Aspartate + 3 ATP →
Urea + Fumarate + 2 ADP + 2 Pi + AMP + PPi
What is the key regulated enzyme in urea synthesis? - Answer Carbamoyl phosphate
synthetase I
-mitochondrial enzyme
-catalyzes commitment step in urea cycle
-activity regulated by N-acetylglutamate in response to -elevated levels of glutamate and
arginine
What is an example of the urea cycle in everyday biochemistry? - Answer Deficiency in enzyme
argininosuccinase inhibits flux thru urea cycle
-causes hyperammonemia and neurologic symptoms
-metabolic disease
-can be treated with low-protein diet supplemented with arginine
-results in argininosuccinate excretion as substitue for urea
What controls the activity of endothelial nitric oxide synthase? - Answer Calcium-calmodulin
binding to endothelial nitric oxide synthase enzyme in response to receptor-mediated signaling
thru G protein-coupled receptors
Which four amino acids are required for the biosynthesis of heme, epinephrine, pheomelanins,
and nitric oxide? Describe the function of each of these amino acid-derived biomolecules in
humans. - Answer -Glycine is required for heme biosynthesis in the first reaction of the
pathway, which is catalyzed by the enzyme δ-aminolevulinate synthase.
-Glycine provides all four nitrogen atoms to the heme ring.
-Heme biomolecules in humans are involved in oxygen transport as components of hemoglobin
and in electron transfer in the electron transport system; for example, in cytochrome c oxidase
(complex IV).
-Tyrosine is the amino acid precursor in the synthesis of epinephrine, an endocrine hormone,
and in the synthesis of pheomelanin, a skin and hair pigment in humans.
-In addition to tyrosine, which provides nitrogen for pheomelanin synthesis, cysteine is also
required, providing the sulfur atom to this pigment.
-Lastly, arginine is the amino acid substrate for nitric oxide production by the enzyme nitric
oxide synthase.
, Why is gout considered a metabolic disease? - Answer because it can be caused by
deregulation of the purine biosynthetic pathway, resulting in uric acid accumulation
How does the cell regulate the substrate specificity of ribonucleotide reductase to maintain
equal amounts of all 4 deoxynucleoside triphosphates (dNTPs)? - Answer By allosteric
regulation of enzyme specificity thru binding of dTTP, dGTP, dATP, or ATP to the substrate
specificity site in the R1 subunit
-when dTTP is bound to the specificity site, more dGDP is produced
-whereas less dCDP and dUDP are generated
-binding of dGTP to the specificity site increases the pool of dADP in the cell but decreases the
pools of dCDP and dUDP
-when ATP or dATP is bound to the specificity site, then levels of dCDP and dUDP are both
increased
Why is efficient dephosphorylation of dUTP by dUTP diphosphohydrolase an important reaction
in the cell? - Answer Because it prevents dUTP from accumulating and mistakenly being
incorporated into DNA
Thymidylate synthesis is required in rapidly dividing cells that need to maintain high rates of
DNA synthesis? - Answer Because cancer cells grow faster than most normal cells in the body,
inhibitors of thymidylate synthesis have been developed as anticancer drugs to block DNA
synthesis
1. Which of the following is correct and most accurately describes the complete urea cycle of
the eukaryotic cell? Choose one:
A. The urea cycle occurs completely within the cytoplasm of the eukaryotic cell.
B. The urea cycle occurs between the inner mitochondrial membrane and the matrix of the
eukaryotic cell.
C. The urea cycle occurs completely within the mitochondrial matrix of the eukaryotic cell.
D. The urea cycle occurs between the mitochondrial matrix and the cytoplasm of the eukaryotic
cell. - Answer D. The urea cycle occurs between the mitochondrial matrix and the cytoplasm
of the eukaryotic cell.
Correct; the urea cycle occurs between the mitochondrial matrix and the cytoplasm of the
eukaryotic cell. The aspartate-argininosuccinate shunt (Krebs bicycle) connects the urea cycle
and the citrate cycle.
with Guaranteed Pass Solutions 2025-
2026 Updated.
The conversion of ribose-1-phosphate to guanosine-5'-triphosphate via the salvage pathway
would require the activity of several enzymes. Choose the answer that lists them in the order
that they would act in this pathway.
A. PRPP synthetase; phosphopentomutase; kinase; kinase; phosphoriboxyl transferase
B. phosphopentomutase; phosphoriboxyl transferase; kinase; PRPP synthetase; kinase
C. PRPP synthetase; phosphoriboxyl transferase; phosphopentomutase; kinase; kinase
D. phosphopentomutase; PRPP synthetase; phosphoriboxyl transferase; kinase; kinase - Answer
D. phosphopentomutase; PRPP synthetase; phosphoriboxyl transferase; kinase; kinase
What molecule signals the endothelial cell to produce nitric oxide, and what is the enzymatic
reaction? - Answer acetylcholine
L-arginine + 1.5 NADP+ + H+ + 2O2 --> citrulline + NO + 1.5 NADPH
Diseases affecting heme biosynthesis as a result of deficiencies in the heme biosynthetic
pathway are called _________.
a. phenylketonuria
b. albinism
c. porphyria
d. alkaptonuria - Answer c. porphyria
What is the mechanism by which glyphosate, the active ingredient in Roundup, kills plants? -
Answer Glyphosate is a competitive inhibitor of plant EPSP synthase
Aspartate is a(n) ________ amino acid, so if a person had a diet that contained no aspartate
then ________.
a. nonessential; they would be unable to synthesize proteins
b. essential; they would be unable to synthesize proteins
c. essential; aspartate could be synthesized from other intermediates
,A person who has alkaptonuria is easily diagnosed from their black urine. What causes the black
color?
a. phenylpyruvate and phenylacetate
b. oxidation of phenylalanine
c. oxidation of homogentisate
d. reduction of acetoacetyl-CoA - Answer c. oxidation of homogentisate
What is the regulatory mechanism by which arginine stimulates flux thru the urea cycle?
A. Arginine stimulates flux through the urea cycle by inhibiting the enzyme nitrogenase.
B. Arginine stimulates the production of N-acetylglutamate which activates arginase.
C. Arginine stimulates the production of the allosteric activator N-acetylglutamate.
D. Arginine stimulates the activity of carbamoyl phosphate synthetase I. - Answer C. Arginine
stimulates the production of the allosteric activator N-acetylglutamate.
Which of the three proteins in the ubiquination pathway is the most responsible for recognizing
the ubiquintated target protein?
a. E2
b. E3
c. E1
d. all 3 of the proteins recognize the target protein - Answer b. E3
In the duodenum, enteropeptidase _.
a. neutralizes the pH of the duodenum to a pH of 7
b. cleaves chymotripsinogen to form chymotrypsin
c. generates peptides and amino acids
d. cleaves trypsinogen to form trypsin - Answer d. cleaves trypsinogen to form trypsin
How is protein ubiquitination regulated? - Answer 2 common mechanisms:
1. biochemical changes in target proteins
such as N-terminal cleavage or phosphorylation
2. biochemical changes in E3 ligases
,What is the net reaction of the urea cycle? - Answer NH4 + + HCO3 − + Aspartate + 3 ATP →
Urea + Fumarate + 2 ADP + 2 Pi + AMP + PPi
What is the key regulated enzyme in urea synthesis? - Answer Carbamoyl phosphate
synthetase I
-mitochondrial enzyme
-catalyzes commitment step in urea cycle
-activity regulated by N-acetylglutamate in response to -elevated levels of glutamate and
arginine
What is an example of the urea cycle in everyday biochemistry? - Answer Deficiency in enzyme
argininosuccinase inhibits flux thru urea cycle
-causes hyperammonemia and neurologic symptoms
-metabolic disease
-can be treated with low-protein diet supplemented with arginine
-results in argininosuccinate excretion as substitue for urea
What controls the activity of endothelial nitric oxide synthase? - Answer Calcium-calmodulin
binding to endothelial nitric oxide synthase enzyme in response to receptor-mediated signaling
thru G protein-coupled receptors
Which four amino acids are required for the biosynthesis of heme, epinephrine, pheomelanins,
and nitric oxide? Describe the function of each of these amino acid-derived biomolecules in
humans. - Answer -Glycine is required for heme biosynthesis in the first reaction of the
pathway, which is catalyzed by the enzyme δ-aminolevulinate synthase.
-Glycine provides all four nitrogen atoms to the heme ring.
-Heme biomolecules in humans are involved in oxygen transport as components of hemoglobin
and in electron transfer in the electron transport system; for example, in cytochrome c oxidase
(complex IV).
-Tyrosine is the amino acid precursor in the synthesis of epinephrine, an endocrine hormone,
and in the synthesis of pheomelanin, a skin and hair pigment in humans.
-In addition to tyrosine, which provides nitrogen for pheomelanin synthesis, cysteine is also
required, providing the sulfur atom to this pigment.
-Lastly, arginine is the amino acid substrate for nitric oxide production by the enzyme nitric
oxide synthase.
, Why is gout considered a metabolic disease? - Answer because it can be caused by
deregulation of the purine biosynthetic pathway, resulting in uric acid accumulation
How does the cell regulate the substrate specificity of ribonucleotide reductase to maintain
equal amounts of all 4 deoxynucleoside triphosphates (dNTPs)? - Answer By allosteric
regulation of enzyme specificity thru binding of dTTP, dGTP, dATP, or ATP to the substrate
specificity site in the R1 subunit
-when dTTP is bound to the specificity site, more dGDP is produced
-whereas less dCDP and dUDP are generated
-binding of dGTP to the specificity site increases the pool of dADP in the cell but decreases the
pools of dCDP and dUDP
-when ATP or dATP is bound to the specificity site, then levels of dCDP and dUDP are both
increased
Why is efficient dephosphorylation of dUTP by dUTP diphosphohydrolase an important reaction
in the cell? - Answer Because it prevents dUTP from accumulating and mistakenly being
incorporated into DNA
Thymidylate synthesis is required in rapidly dividing cells that need to maintain high rates of
DNA synthesis? - Answer Because cancer cells grow faster than most normal cells in the body,
inhibitors of thymidylate synthesis have been developed as anticancer drugs to block DNA
synthesis
1. Which of the following is correct and most accurately describes the complete urea cycle of
the eukaryotic cell? Choose one:
A. The urea cycle occurs completely within the cytoplasm of the eukaryotic cell.
B. The urea cycle occurs between the inner mitochondrial membrane and the matrix of the
eukaryotic cell.
C. The urea cycle occurs completely within the mitochondrial matrix of the eukaryotic cell.
D. The urea cycle occurs between the mitochondrial matrix and the cytoplasm of the eukaryotic
cell. - Answer D. The urea cycle occurs between the mitochondrial matrix and the cytoplasm
of the eukaryotic cell.
Correct; the urea cycle occurs between the mitochondrial matrix and the cytoplasm of the
eukaryotic cell. The aspartate-argininosuccinate shunt (Krebs bicycle) connects the urea cycle
and the citrate cycle.
