CHEM 210 Exam 4 - Biochemistry Review
Comprehensive Review Examination | 100 Questions | Biochemistry
1. The cytochrome P450 enzyme system is primarily involved in which phase of drug metabolism?
A. Phase I (functionalization) [CORRECT]
B. Phase II (conjugation)
C. Phase III (transport)
D. Phase IV (excretion)
Correct Answer: A
Rationale: Correct because cytochrome P450 enzymes catalyze Phase I reactions including hydroxylation, oxidation,
and dealkylation that introduce or expose functional groups on drug molecules. This matches the role of CYP
enzymes in the oxidative metabolism of xenobiotics.
Clinical Scenario / Case-Based Question
2. A 45-year-old patient with uncontrolled type 2 diabetes presents with elevated blood glucose (320 mg/dL),
increased plasma ketone bodies, and a blood pH of 7.25. Which metabolic pathway is most likely responsible
for the elevated ketone bodies?
A. Increased glycolysis in the liver
B. Increased beta-oxidation and hepatic ketogenesis [CORRECT]
C. Decreased fatty acid synthesis in adipose tissue
D. Impaired gluconeogenesis in the liver
Correct Answer: B
Rationale: Correct because in uncontrolled diabetes, insulin deficiency promotes excessive lipolysis and hepatic
beta-oxidation, producing large amounts of acetyl-CoA that exceeds the capacity of the TCA cycle, leading to ketone
body overproduction (ketogenesis). This matches the pathophysiology of diabetic ketoacidosis.
3. Which polysaccharide serves as a structural component in the exoskeleton of arthropods?
A. Cellulose
B. Starch
C. Glycogen
D. Chitin [CORRECT]
Correct Answer: D
Rationale: Correct because chitin is a linear polysaccharide of N-acetylglucosamine units linked by
beta-1,4-glycosidic bonds, forming the structural framework of arthropod exoskeletons and fungal cell walls. This
matches the biological function of chitin as a structural polysaccharide.
4. Which RNA polymerase is responsible for transcribing mRNA in eukaryotic cells?
A. RNA polymerase I
B. RNA polymerase II [CORRECT]
C. RNA polymerase III
D. RNA polymerase IV
Correct Answer: B
Rationale: Correct because RNA polymerase II transcribes all protein-coding genes into messenger RNA (mRNA) as
well as several small nuclear RNAs. This matches the functional division of labor among the three eukaryotic
nuclear RNA polymerases.
5. According to the Beer-Lambert law, absorbance is directly proportional to which of the following?
A. Transmittance
B. Concentration of the solute [CORRECT]
, C. Inverse of the path length
D. Wavelength of incident light
Correct Answer: B
Rationale: Correct because the Beer-Lambert law states that A = ecl, where absorbance (A) is directly proportional
to the concentration (c) of the absorbing solute, the molar extinction coefficient (e), and the path length (l). This
matches the fundamental principle underlying spectrophotometric quantitation.
6. Which metal ion is required as a cofactor by cytochrome c oxidase (Complex IV) in the electron transport
chain?
A. Magnesium
B. Zinc
C. Iron and copper [CORRECT]
D. Manganese
Correct Answer: C
Rationale: Correct because cytochrome c oxidase contains both heme iron (heme a and heme a3) and copper centers
(CuA and CuB) that are essential for its electron transfer and oxygen reduction functions. This matches the
metalloprotein composition of Complex IV.
7. A researcher treats a protein with urea and beta-mercaptoethanol, then removes both agents. The protein
regains its native conformation and biological activity. Which level of protein structure is primarily
responsible for directing this refolding?
A. Primary structure [CORRECT]
B. Secondary structure
C. Tertiary structure
D. Quaternary structure
Correct Answer: A
Rationale: Correct because the primary structure (amino acid sequence) encodes all the information necessary for
the protein to fold into its native three-dimensional conformation. This matches Anfinsen's dogma which states that
the native structure is determined solely by the amino acid sequence.
8. Histone deacetylases (HDACs) remove which chemical group from histone tails?
A. Methyl groups
B. Phosphate groups
C. Acetyl groups [CORRECT]
D. Ubiquitin molecules
Correct Answer: C
Rationale: Correct because histone deacetylases catalyze the removal of acetyl groups from lysine residues on
histone tails, which typically leads to chromatin compaction and transcriptional repression. This matches the
enzymatic function of HDACs in epigenetic regulation.
9. Which of the following enzymes is unique to gluconeogenesis and not found in glycolysis?
A. Phosphoglycerate kinase
B. Fructose-1,6-bisphosphatase [CORRECT]
C. Enolase
D. Glyceraldehyde-3-phosphate dehydrogenase
Correct Answer: B
Rationale: Correct because fructose-1,6-bisphosphatase catalyzes the irreversible hydrolysis of
fructose-1,6-bisphosphate to fructose-6-phosphate, a bypass reaction that exists only in gluconeogenesis. This
matches the three irreversible steps that require unique enzymes in the gluconeogenic pathway.
10. The alpha-helix and beta-sheet are both examples of which level of protein structure?
A. Primary structure
B. Secondary structure [CORRECT]
, C. Tertiary structure
D. Quaternary structure
Correct Answer: B
Rationale: Correct because secondary structure refers to local regular structures stabilized primarily by hydrogen
bonds between backbone amide and carbonyl groups, with the alpha-helix and beta-sheet being the two most
common types. This matches the standard classification of protein structural hierarchy.
11. Enhancers are cis-acting regulatory elements that can increase transcription. Which characteristic best
describes how enhancers function?
A. They must be located immediately upstream of the promoter
B. They function independently of distance and orientation relative to the gene [CORRECT]
C. They encode small regulatory RNAs
D. They bind directly to RNA polymerase II
Correct Answer: B
Rationale: Correct because enhancers can be located thousands of base pairs away from the promoter and function
in either orientation, with DNA looping bringing them into proximity with the transcription machinery. This
matches the defining features of enhancer elements in eukaryotic gene regulation.
12. What is the first intermediate formed in the urea cycle that contains nitrogen from both ammonia and
aspartate?
A. Carbamoyl phosphate
B. Citrulline
C. Argininosuccinate [CORRECT]
D. Arginine
Correct Answer: C
Rationale: Correct because argininosuccinate is formed when citrulline combines with aspartate, incorporating the
amino group from aspartate into the molecule that already carries nitrogen from carbamoyl phosphate (derived
from ammonia). This matches the biochemical mechanism of nitrogen incorporation in the urea cycle.
13. Which amino acid is both glucogenic and ketogenic?
A. Leucine
B. Lysine
C. Isoleucine [CORRECT]
D. Alanine
Correct Answer: C
Rationale: Correct because isoleucine is catabolized to yield both acetyl-CoA (a ketogenic product) and
succinyl-CoA (a glucogenic product), making it one of only two purely glucogenic and ketogenic amino acids along
with phenylalanine, tyrosine, and tryptophan. This matches the metabolic classification of amino acids based on
their degradation products.
14. Methotrexate is a chemotherapeutic agent that inhibits which enzyme?
A. Thymidylate synthase
B. Dihydrofolate reductase [CORRECT]
C. Ribonucleotide reductase
D. IMP dehydrogenase
Correct Answer: B
Rationale: Correct because methotrexate is a structural analog of folic acid that competitively inhibits dihydrofolate
reductase (DHFR), depleting tetrahydrofolate and thereby inhibiting purine and thymidylate synthesis. This
matches the mechanism of action of methotrexate as an anticancer drug.
15. Under standard biochemical conditions (pH 7.0), which of the following has the highest phosphoryl group
transfer potential?
A. Glucose-6-phosphate
Comprehensive Review Examination | 100 Questions | Biochemistry
1. The cytochrome P450 enzyme system is primarily involved in which phase of drug metabolism?
A. Phase I (functionalization) [CORRECT]
B. Phase II (conjugation)
C. Phase III (transport)
D. Phase IV (excretion)
Correct Answer: A
Rationale: Correct because cytochrome P450 enzymes catalyze Phase I reactions including hydroxylation, oxidation,
and dealkylation that introduce or expose functional groups on drug molecules. This matches the role of CYP
enzymes in the oxidative metabolism of xenobiotics.
Clinical Scenario / Case-Based Question
2. A 45-year-old patient with uncontrolled type 2 diabetes presents with elevated blood glucose (320 mg/dL),
increased plasma ketone bodies, and a blood pH of 7.25. Which metabolic pathway is most likely responsible
for the elevated ketone bodies?
A. Increased glycolysis in the liver
B. Increased beta-oxidation and hepatic ketogenesis [CORRECT]
C. Decreased fatty acid synthesis in adipose tissue
D. Impaired gluconeogenesis in the liver
Correct Answer: B
Rationale: Correct because in uncontrolled diabetes, insulin deficiency promotes excessive lipolysis and hepatic
beta-oxidation, producing large amounts of acetyl-CoA that exceeds the capacity of the TCA cycle, leading to ketone
body overproduction (ketogenesis). This matches the pathophysiology of diabetic ketoacidosis.
3. Which polysaccharide serves as a structural component in the exoskeleton of arthropods?
A. Cellulose
B. Starch
C. Glycogen
D. Chitin [CORRECT]
Correct Answer: D
Rationale: Correct because chitin is a linear polysaccharide of N-acetylglucosamine units linked by
beta-1,4-glycosidic bonds, forming the structural framework of arthropod exoskeletons and fungal cell walls. This
matches the biological function of chitin as a structural polysaccharide.
4. Which RNA polymerase is responsible for transcribing mRNA in eukaryotic cells?
A. RNA polymerase I
B. RNA polymerase II [CORRECT]
C. RNA polymerase III
D. RNA polymerase IV
Correct Answer: B
Rationale: Correct because RNA polymerase II transcribes all protein-coding genes into messenger RNA (mRNA) as
well as several small nuclear RNAs. This matches the functional division of labor among the three eukaryotic
nuclear RNA polymerases.
5. According to the Beer-Lambert law, absorbance is directly proportional to which of the following?
A. Transmittance
B. Concentration of the solute [CORRECT]
, C. Inverse of the path length
D. Wavelength of incident light
Correct Answer: B
Rationale: Correct because the Beer-Lambert law states that A = ecl, where absorbance (A) is directly proportional
to the concentration (c) of the absorbing solute, the molar extinction coefficient (e), and the path length (l). This
matches the fundamental principle underlying spectrophotometric quantitation.
6. Which metal ion is required as a cofactor by cytochrome c oxidase (Complex IV) in the electron transport
chain?
A. Magnesium
B. Zinc
C. Iron and copper [CORRECT]
D. Manganese
Correct Answer: C
Rationale: Correct because cytochrome c oxidase contains both heme iron (heme a and heme a3) and copper centers
(CuA and CuB) that are essential for its electron transfer and oxygen reduction functions. This matches the
metalloprotein composition of Complex IV.
7. A researcher treats a protein with urea and beta-mercaptoethanol, then removes both agents. The protein
regains its native conformation and biological activity. Which level of protein structure is primarily
responsible for directing this refolding?
A. Primary structure [CORRECT]
B. Secondary structure
C. Tertiary structure
D. Quaternary structure
Correct Answer: A
Rationale: Correct because the primary structure (amino acid sequence) encodes all the information necessary for
the protein to fold into its native three-dimensional conformation. This matches Anfinsen's dogma which states that
the native structure is determined solely by the amino acid sequence.
8. Histone deacetylases (HDACs) remove which chemical group from histone tails?
A. Methyl groups
B. Phosphate groups
C. Acetyl groups [CORRECT]
D. Ubiquitin molecules
Correct Answer: C
Rationale: Correct because histone deacetylases catalyze the removal of acetyl groups from lysine residues on
histone tails, which typically leads to chromatin compaction and transcriptional repression. This matches the
enzymatic function of HDACs in epigenetic regulation.
9. Which of the following enzymes is unique to gluconeogenesis and not found in glycolysis?
A. Phosphoglycerate kinase
B. Fructose-1,6-bisphosphatase [CORRECT]
C. Enolase
D. Glyceraldehyde-3-phosphate dehydrogenase
Correct Answer: B
Rationale: Correct because fructose-1,6-bisphosphatase catalyzes the irreversible hydrolysis of
fructose-1,6-bisphosphate to fructose-6-phosphate, a bypass reaction that exists only in gluconeogenesis. This
matches the three irreversible steps that require unique enzymes in the gluconeogenic pathway.
10. The alpha-helix and beta-sheet are both examples of which level of protein structure?
A. Primary structure
B. Secondary structure [CORRECT]
, C. Tertiary structure
D. Quaternary structure
Correct Answer: B
Rationale: Correct because secondary structure refers to local regular structures stabilized primarily by hydrogen
bonds between backbone amide and carbonyl groups, with the alpha-helix and beta-sheet being the two most
common types. This matches the standard classification of protein structural hierarchy.
11. Enhancers are cis-acting regulatory elements that can increase transcription. Which characteristic best
describes how enhancers function?
A. They must be located immediately upstream of the promoter
B. They function independently of distance and orientation relative to the gene [CORRECT]
C. They encode small regulatory RNAs
D. They bind directly to RNA polymerase II
Correct Answer: B
Rationale: Correct because enhancers can be located thousands of base pairs away from the promoter and function
in either orientation, with DNA looping bringing them into proximity with the transcription machinery. This
matches the defining features of enhancer elements in eukaryotic gene regulation.
12. What is the first intermediate formed in the urea cycle that contains nitrogen from both ammonia and
aspartate?
A. Carbamoyl phosphate
B. Citrulline
C. Argininosuccinate [CORRECT]
D. Arginine
Correct Answer: C
Rationale: Correct because argininosuccinate is formed when citrulline combines with aspartate, incorporating the
amino group from aspartate into the molecule that already carries nitrogen from carbamoyl phosphate (derived
from ammonia). This matches the biochemical mechanism of nitrogen incorporation in the urea cycle.
13. Which amino acid is both glucogenic and ketogenic?
A. Leucine
B. Lysine
C. Isoleucine [CORRECT]
D. Alanine
Correct Answer: C
Rationale: Correct because isoleucine is catabolized to yield both acetyl-CoA (a ketogenic product) and
succinyl-CoA (a glucogenic product), making it one of only two purely glucogenic and ketogenic amino acids along
with phenylalanine, tyrosine, and tryptophan. This matches the metabolic classification of amino acids based on
their degradation products.
14. Methotrexate is a chemotherapeutic agent that inhibits which enzyme?
A. Thymidylate synthase
B. Dihydrofolate reductase [CORRECT]
C. Ribonucleotide reductase
D. IMP dehydrogenase
Correct Answer: B
Rationale: Correct because methotrexate is a structural analog of folic acid that competitively inhibits dihydrofolate
reductase (DHFR), depleting tetrahydrofolate and thereby inhibiting purine and thymidylate synthesis. This
matches the mechanism of action of methotrexate as an anticancer drug.
15. Under standard biochemical conditions (pH 7.0), which of the following has the highest phosphoryl group
transfer potential?
A. Glucose-6-phosphate
