BIOCHEM 210 Final Exam Biochemistry Portage Learning Question
Bank (Latest 2026/2027 Edition) – 100% Correct Questions, Answers &
Detailed Rationales
Total Questions: 50
Time Allowed: 120 Minutes
Instructions: Select the BEST answer for each multiple-choice question. For True/False
questions, indicate if the statement is True or False.
SECTION 1: FOUNDATIONS OF BIOCHEMISTRY (Water, pH, Buffers,
Biomolecules)
Questions 1–6
Question 1
A buffer solution contains 0.10 M acetic acid (pKa = 4.76) and 0.15 M sodium acetate.
What is the approximate pH of this buffer?
A. 4.58
B. 4.76
C. 4.94
D. 5.12
Correct Answer: C
,Rationale: Using the Henderson-Hasselbalch equation, pH = pKa + log([A⁻]/[HA]) = 4.76
+ log(0.15/0.10) = 4.76 + log(1.5) = 4.76 + 0.18 = 4.94. The pH rises above pKa because
the conjugate base concentration exceeds the weak acid concentration.
Question 2
Which property of water is most directly responsible for its unusually high specific heat
capacity?
A. The small molecular size of water
B. The extensive hydrogen bonding network between water molecules
C. The linear geometry of the water molecule
D. The nonpolar nature of the O–H bond
Correct Answer: B
Rationale: Hydrogen bonding creates a network where substantial energy is required to
break intermolecular attractions before increasing kinetic energy (temperature), giving
water its high specific heat. Option A is incorrect because molecular size does not
determine heat capacity. Option C is incorrect because water has a bent, not linear,
geometry. Option D is incorrect because the O–H bond is highly polar, not nonpolar.
Question 3
In a biological system at pH 7.4, which functional group would be predominantly
protonated?
A. Carboxylic acid (pKa ≈ 4.5)
B. Amine (pKa ≈ 9.5)
C. Phosphate (pKa ≈ 6.8)
D. Sulfhydryl (pKa ≈ 8.3)
Correct Answer: B
, Rationale: A group is predominantly protonated when pH < pKa; for the amine with pKa
9.5, pH 7.4 is well below its pKa, so –NH₃⁺ predominates. Option A is incorrect because
carboxylic acid is deprotonated at pH 7.4 (pH > pKa). Option C is incorrect because
phosphate at pKa 6.8 is slightly deprotonated at pH 7.4. Option D is incorrect because
sulfhydryl at pKa 8.3 is mostly protonated but less so than the amine.
Question 4
True or False: Hydrophobic interactions are driven primarily by an attractive force
between nonpolar molecules.
Answer: False
Rationale: Hydrophobic interactions are not true attractive forces; they arise because
water molecules form ordered cages around nonpolar groups, which is entropically
unfavorable. Aggregation of nonpolar molecules releases ordered water, increasing
entropy and lowering free energy.
Question 5
Which statement best describes the role of carbon in biomolecules?
A. Carbon forms only single bonds, limiting structural diversity.
B. Carbon's tetravalency and ability to form stable covalent bonds with itself enable the
construction of complex macromolecules.
C. Carbon is electronegative enough to form hydrogen bonds with water directly.
D. Carbon primarily exists in ionic form within biological systems.
Correct Answer: B
Rationale: Carbon's four valence electrons allow diverse bonding patterns (single,
double, triple bonds, chains, rings), forming the backbone of all major biomolecules.
Option A is incorrect because carbon readily forms double and triple bonds. Option C is
Bank (Latest 2026/2027 Edition) – 100% Correct Questions, Answers &
Detailed Rationales
Total Questions: 50
Time Allowed: 120 Minutes
Instructions: Select the BEST answer for each multiple-choice question. For True/False
questions, indicate if the statement is True or False.
SECTION 1: FOUNDATIONS OF BIOCHEMISTRY (Water, pH, Buffers,
Biomolecules)
Questions 1–6
Question 1
A buffer solution contains 0.10 M acetic acid (pKa = 4.76) and 0.15 M sodium acetate.
What is the approximate pH of this buffer?
A. 4.58
B. 4.76
C. 4.94
D. 5.12
Correct Answer: C
,Rationale: Using the Henderson-Hasselbalch equation, pH = pKa + log([A⁻]/[HA]) = 4.76
+ log(0.15/0.10) = 4.76 + log(1.5) = 4.76 + 0.18 = 4.94. The pH rises above pKa because
the conjugate base concentration exceeds the weak acid concentration.
Question 2
Which property of water is most directly responsible for its unusually high specific heat
capacity?
A. The small molecular size of water
B. The extensive hydrogen bonding network between water molecules
C. The linear geometry of the water molecule
D. The nonpolar nature of the O–H bond
Correct Answer: B
Rationale: Hydrogen bonding creates a network where substantial energy is required to
break intermolecular attractions before increasing kinetic energy (temperature), giving
water its high specific heat. Option A is incorrect because molecular size does not
determine heat capacity. Option C is incorrect because water has a bent, not linear,
geometry. Option D is incorrect because the O–H bond is highly polar, not nonpolar.
Question 3
In a biological system at pH 7.4, which functional group would be predominantly
protonated?
A. Carboxylic acid (pKa ≈ 4.5)
B. Amine (pKa ≈ 9.5)
C. Phosphate (pKa ≈ 6.8)
D. Sulfhydryl (pKa ≈ 8.3)
Correct Answer: B
, Rationale: A group is predominantly protonated when pH < pKa; for the amine with pKa
9.5, pH 7.4 is well below its pKa, so –NH₃⁺ predominates. Option A is incorrect because
carboxylic acid is deprotonated at pH 7.4 (pH > pKa). Option C is incorrect because
phosphate at pKa 6.8 is slightly deprotonated at pH 7.4. Option D is incorrect because
sulfhydryl at pKa 8.3 is mostly protonated but less so than the amine.
Question 4
True or False: Hydrophobic interactions are driven primarily by an attractive force
between nonpolar molecules.
Answer: False
Rationale: Hydrophobic interactions are not true attractive forces; they arise because
water molecules form ordered cages around nonpolar groups, which is entropically
unfavorable. Aggregation of nonpolar molecules releases ordered water, increasing
entropy and lowering free energy.
Question 5
Which statement best describes the role of carbon in biomolecules?
A. Carbon forms only single bonds, limiting structural diversity.
B. Carbon's tetravalency and ability to form stable covalent bonds with itself enable the
construction of complex macromolecules.
C. Carbon is electronegative enough to form hydrogen bonds with water directly.
D. Carbon primarily exists in ionic form within biological systems.
Correct Answer: B
Rationale: Carbon's four valence electrons allow diverse bonding patterns (single,
double, triple bonds, chains, rings), forming the backbone of all major biomolecules.
Option A is incorrect because carbon readily forms double and triple bonds. Option C is
