BCH 4053 Final Exam V3 | BCH 4053
Biochemistry I | Actual Q&A with
Rationale (BCH4053 Final Exam) |
University of Central Florida
1. Which of the following amino acids is most likely to be found in the interior of a water-
soluble globular protein?
A. Serine
B. Aspartate
C. Phenylalanine
D. Lysine
Answer: C
Rationale: Phenylalanine is a nonpolar, hydrophobic amino acid that avoids contact with
the aqueous environment. In a globular protein, hydrophobic residues are sequestered in
the core to maximize the entropy of surrounding water molecules. Serine, Aspartate, and
Lysine are polar or charged and are typically found on the protein surface.
2. In the Henderson-Hasselbalch equation, what occurs when the concentration of the
conjugate base equals the concentration of the weak acid?
A. The pH is zero
B. The solution is at maximum acidity
,C. The pH is equal to the pKa
D. The pKa becomes double the pH
Answer: C
Rationale: The Henderson-Hasselbalch equation is defined as pH = pKa + log([A-]/[HA]).
When [A-] equals [HA], the ratio is 1 and the log(1) is 0, resulting in pH = pKa. This point
represents the center of the buffering region where the system is most resistant to pH
changes.
3. Which type of interaction is primarily responsible for stabilizing the secondary structure of
proteins, such as alpha-helices and beta-sheets?
A. Ionic bonds between acidic and basic residues
B. Disulfide bridges between Cysteines
C. Hydrophobic interactions between R-groups
D. Hydrogen bonds between backbone atoms
Answer: D
Rationale: Secondary structure is specifically defined by the spatial arrangement of the
polypeptide backbone. Hydrogen bonds form between the carbonyl oxygen and the amide
hydrogen of the peptide bond. While R-groups influence which structures form, they do not
provide the primary stabilizing bonds for these specific patterns.
, 4. What is the effect of a noncompetitive inhibitor on the Michaelis-Menten kinetic
parameters of an enzyme?
A. Km increases, Vmax stays the same
B. Km decreases, Vmax decreases
C. Vmax decreases, Km stays the same
D. Vmax increases, Km increases
Answer: C
Rationale: Noncompetitive inhibitors bind to a site other than the active site and can bind
to both the free enzyme and the enzyme-substrate complex. This reduces the total
concentration of functional enzyme, thereby lowering the Vmax. Since the inhibitor does
not interfere with substrate binding at the active site, the Km remains unchanged.
5. Which of the following statements regarding the peptide bond is true?
A. It is a triple bond with no rotation
B. It forms between the R-groups of amino acids
C. It is highly flexible and rotates freely
D. It has partial double-bond character and is planar
Answer: D
Rationale: The peptide bond results from a resonance structure between the carbonyl
group and the nitrogen atom. This resonance gives the C-N bond partial double-bond
Biochemistry I | Actual Q&A with
Rationale (BCH4053 Final Exam) |
University of Central Florida
1. Which of the following amino acids is most likely to be found in the interior of a water-
soluble globular protein?
A. Serine
B. Aspartate
C. Phenylalanine
D. Lysine
Answer: C
Rationale: Phenylalanine is a nonpolar, hydrophobic amino acid that avoids contact with
the aqueous environment. In a globular protein, hydrophobic residues are sequestered in
the core to maximize the entropy of surrounding water molecules. Serine, Aspartate, and
Lysine are polar or charged and are typically found on the protein surface.
2. In the Henderson-Hasselbalch equation, what occurs when the concentration of the
conjugate base equals the concentration of the weak acid?
A. The pH is zero
B. The solution is at maximum acidity
,C. The pH is equal to the pKa
D. The pKa becomes double the pH
Answer: C
Rationale: The Henderson-Hasselbalch equation is defined as pH = pKa + log([A-]/[HA]).
When [A-] equals [HA], the ratio is 1 and the log(1) is 0, resulting in pH = pKa. This point
represents the center of the buffering region where the system is most resistant to pH
changes.
3. Which type of interaction is primarily responsible for stabilizing the secondary structure of
proteins, such as alpha-helices and beta-sheets?
A. Ionic bonds between acidic and basic residues
B. Disulfide bridges between Cysteines
C. Hydrophobic interactions between R-groups
D. Hydrogen bonds between backbone atoms
Answer: D
Rationale: Secondary structure is specifically defined by the spatial arrangement of the
polypeptide backbone. Hydrogen bonds form between the carbonyl oxygen and the amide
hydrogen of the peptide bond. While R-groups influence which structures form, they do not
provide the primary stabilizing bonds for these specific patterns.
, 4. What is the effect of a noncompetitive inhibitor on the Michaelis-Menten kinetic
parameters of an enzyme?
A. Km increases, Vmax stays the same
B. Km decreases, Vmax decreases
C. Vmax decreases, Km stays the same
D. Vmax increases, Km increases
Answer: C
Rationale: Noncompetitive inhibitors bind to a site other than the active site and can bind
to both the free enzyme and the enzyme-substrate complex. This reduces the total
concentration of functional enzyme, thereby lowering the Vmax. Since the inhibitor does
not interfere with substrate binding at the active site, the Km remains unchanged.
5. Which of the following statements regarding the peptide bond is true?
A. It is a triple bond with no rotation
B. It forms between the R-groups of amino acids
C. It is highly flexible and rotates freely
D. It has partial double-bond character and is planar
Answer: D
Rationale: The peptide bond results from a resonance structure between the carbonyl
group and the nitrogen atom. This resonance gives the C-N bond partial double-bond
