BIOCHEM 210 FINAL EXAM 2026/2027 | Comprehensive
Biochemistry | Portage Learning | Complete Q&A with
Verified Answers | Pass Guaranteed - A+ Graded
Q1: Which level of protein structure is primarily disrupted by treating a protein with 8 M
urea?
A. Primary structure
B. Secondary structure
C. Tertiary structure [CORRECT]
D. Quaternary structure only
Correct Answer: C
Rationale: 8 M urea is a chaotropic agent that disrupts non-covalent interactions
including hydrogen bonds, ionic bonds, and hydrophobic interactions that stabilize the
three-dimensional folding of a single polypeptide chain (tertiary structure). While urea
can eventually affect secondary structures, its primary target is the hydrophobic core
collapse and other interactions maintaining tertiary architecture. Distractor A is
incorrect because primary structure (peptide bonds) requires proteases or harsh acid
hydrolysis to break. Distractor B is partially affected but not primarily—secondary
structures are more susceptible to pH extremes or detergents like SDS. Distractor D is
incorrect because while quaternary structure may be affected, urea primarily targets the
folding of individual subunits (tertiary) rather than exclusively subunit-subunit
interactions.
Q2: In enzyme kinetics, what does the Michaelis constant (Km) represent?
A. The maximum velocity of the reaction
B. The substrate concentration at which reaction velocity is half of Vmax [CORRECT]
C. The catalytic efficiency of the enzyme
,D. The equilibrium constant for the reaction
Correct Answer: B
Rationale: By definition, Km equals the substrate concentration [S] when v = Vmax/2,
reflecting the enzyme's apparent affinity for substrate (lower Km = higher affinity).
Distractor A describes Vmax, not Km. Distractor C describes kcat/Km, the specificity
constant measuring catalytic efficiency. Distractor D is incorrect because Km is a kinetic
parameter (k-1 + k2)/k1 under Briggs-Haldane steady-state assumptions, not a
thermodynamic equilibrium constant. The Km approximates but does not equal the
dissociation constant Kd unless k2 << k-1.
Q3: Which amino acid is classified as both ketogenic and glucogenic?
A. Leucine
B. Lysine
C. Isoleucine [CORRECT]
D. Tyrosine
Correct Answer: C
Rationale: Isoleucine degrades to succinyl-CoA (glucogenic, enters TCA cycle) and
acetyl-CoA/acetoacetyl-CoA (ketogenic, cannot form glucose). Distractor A (leucine)
and B (lysine) are exclusively ketogenic, degrading only to acetyl-CoA or
acetoacetyl-CoA. Distractor D (tyrosine) is both ketogenic and glucogenic, but the
question asks for the best answer among choices—isoleucine is the classic
branched-chain example. Note: Phenylalanine, tryptophan, and tyrosine are also
dual-classified, but isoleucine is the only branched-chain amino acid with this property.
Q4: During glycolysis, which enzyme catalyzes the first committed step and is the major
regulatory point?
A. Hexokinase
, B. Phosphofructokinase-1 (PFK-1) [CORRECT]
C. Pyruvate kinase
D. Phosphoglycerate kinase
Correct Answer: B
Rationale: PFK-1 catalyzes the irreversible phosphorylation of fructose-6-phosphate to
fructose-1,6-bisphosphate, the first reaction unique to glycolysis (committed step). It is
allosterically inhibited by ATP and citrate, activated by AMP and
fructose-2,6-bisphosphate. Distractor A (hexokinase) is regulated but not the committed
step—glucose-6-phosphate can enter glycogen synthesis or PPP. Distractor C (pyruvate
kinase) is regulated but acts late in the pathway. Distractor D is a reversible enzyme
near equilibrium with no regulatory significance.
Q5: Which of the following is NOT a product of the pyruvate dehydrogenase complex
reaction?
A. Acetyl-CoA
B. NADH
C. CO₂
D. FADH₂ [CORRECT]
Correct Answer: D
Rationale: The PDC converts pyruvate → acetyl-CoA + CO₂ + NADH, using TPP,
lipoamide, FAD, and NAD⁺ as cofactors. FAD is reduced to FADH₂ during catalysis but is
reoxidized by NAD⁺ to regenerate the lipoamide; FADH₂ is not released as a final
product. Distractor A, B, and C are all true products. This distinction is crucial: while
FADH₂ forms transiently within the enzyme complex, only NADH is released to the
mitochondrial matrix for the electron transport chain.
Q6: In the citric acid cycle, which enzyme catalyzes a substrate-level phosphorylation?
A. Citrate synthase
Biochemistry | Portage Learning | Complete Q&A with
Verified Answers | Pass Guaranteed - A+ Graded
Q1: Which level of protein structure is primarily disrupted by treating a protein with 8 M
urea?
A. Primary structure
B. Secondary structure
C. Tertiary structure [CORRECT]
D. Quaternary structure only
Correct Answer: C
Rationale: 8 M urea is a chaotropic agent that disrupts non-covalent interactions
including hydrogen bonds, ionic bonds, and hydrophobic interactions that stabilize the
three-dimensional folding of a single polypeptide chain (tertiary structure). While urea
can eventually affect secondary structures, its primary target is the hydrophobic core
collapse and other interactions maintaining tertiary architecture. Distractor A is
incorrect because primary structure (peptide bonds) requires proteases or harsh acid
hydrolysis to break. Distractor B is partially affected but not primarily—secondary
structures are more susceptible to pH extremes or detergents like SDS. Distractor D is
incorrect because while quaternary structure may be affected, urea primarily targets the
folding of individual subunits (tertiary) rather than exclusively subunit-subunit
interactions.
Q2: In enzyme kinetics, what does the Michaelis constant (Km) represent?
A. The maximum velocity of the reaction
B. The substrate concentration at which reaction velocity is half of Vmax [CORRECT]
C. The catalytic efficiency of the enzyme
,D. The equilibrium constant for the reaction
Correct Answer: B
Rationale: By definition, Km equals the substrate concentration [S] when v = Vmax/2,
reflecting the enzyme's apparent affinity for substrate (lower Km = higher affinity).
Distractor A describes Vmax, not Km. Distractor C describes kcat/Km, the specificity
constant measuring catalytic efficiency. Distractor D is incorrect because Km is a kinetic
parameter (k-1 + k2)/k1 under Briggs-Haldane steady-state assumptions, not a
thermodynamic equilibrium constant. The Km approximates but does not equal the
dissociation constant Kd unless k2 << k-1.
Q3: Which amino acid is classified as both ketogenic and glucogenic?
A. Leucine
B. Lysine
C. Isoleucine [CORRECT]
D. Tyrosine
Correct Answer: C
Rationale: Isoleucine degrades to succinyl-CoA (glucogenic, enters TCA cycle) and
acetyl-CoA/acetoacetyl-CoA (ketogenic, cannot form glucose). Distractor A (leucine)
and B (lysine) are exclusively ketogenic, degrading only to acetyl-CoA or
acetoacetyl-CoA. Distractor D (tyrosine) is both ketogenic and glucogenic, but the
question asks for the best answer among choices—isoleucine is the classic
branched-chain example. Note: Phenylalanine, tryptophan, and tyrosine are also
dual-classified, but isoleucine is the only branched-chain amino acid with this property.
Q4: During glycolysis, which enzyme catalyzes the first committed step and is the major
regulatory point?
A. Hexokinase
, B. Phosphofructokinase-1 (PFK-1) [CORRECT]
C. Pyruvate kinase
D. Phosphoglycerate kinase
Correct Answer: B
Rationale: PFK-1 catalyzes the irreversible phosphorylation of fructose-6-phosphate to
fructose-1,6-bisphosphate, the first reaction unique to glycolysis (committed step). It is
allosterically inhibited by ATP and citrate, activated by AMP and
fructose-2,6-bisphosphate. Distractor A (hexokinase) is regulated but not the committed
step—glucose-6-phosphate can enter glycogen synthesis or PPP. Distractor C (pyruvate
kinase) is regulated but acts late in the pathway. Distractor D is a reversible enzyme
near equilibrium with no regulatory significance.
Q5: Which of the following is NOT a product of the pyruvate dehydrogenase complex
reaction?
A. Acetyl-CoA
B. NADH
C. CO₂
D. FADH₂ [CORRECT]
Correct Answer: D
Rationale: The PDC converts pyruvate → acetyl-CoA + CO₂ + NADH, using TPP,
lipoamide, FAD, and NAD⁺ as cofactors. FAD is reduced to FADH₂ during catalysis but is
reoxidized by NAD⁺ to regenerate the lipoamide; FADH₂ is not released as a final
product. Distractor A, B, and C are all true products. This distinction is crucial: while
FADH₂ forms transiently within the enzyme complex, only NADH is released to the
mitochondrial matrix for the electron transport chain.
Q6: In the citric acid cycle, which enzyme catalyzes a substrate-level phosphorylation?
A. Citrate synthase
