BCH 4053 Exam 1 V3 | BCH 4053 Biochemistry I | Actual Q&A with
Rationale (BCH4053 Exam 1) | University of Central Florida
1. Which of the following properties of water is primarily responsible for the hydrophobic
effect seen in protein folding?
A. High dielectric constant
B. Ability to form four hydrogen bonds
C. Tendency to maximize entropy by excluding nonpolar solutes
D. High specific heat capacity
Answer: C
Explanation: The hydrophobic effect is driven by the increase in entropy of water
molecules when nonpolar surfaces aggregate. When nonpolar molecules are separate,
water forms highly ordered clathrate cages around them, which is entropically unfavorable.
By clustering the nonpolar molecules, the total surface area decreases, releasing water
molecules into the bulk solvent and increasing the overall entropy of the system.
2. If a buffer solution has a pH of 7.4 and the pKa of the acid component is 6.8, what is the
ratio of [A-] to [HA]?
A. 1:1
B. 2:1
C. 10:1
D. 4:1
Answer: D
Explanation: Using the Henderson-Hasselbalch equation (pH = pKa + log([A-]/[HA])), we
substitute the given values: 7.4 = 6.8 + log([A-]/[HA]). This simplifies to 0.6 = log([A-
]/[HA]). Calculating the antilog (10^0.6) gives approximately 3.98, which rounds to a ratio
of 4:1.
3. Which amino acid contains a secondary amine within its structure, leading to significant
conformational constraints?
A. Histidine
B. Tryptophan
C. Glycine
D. Proline
,Answer: D
Explanation: Proline is unique because its side chain is covalently bonded to both the
nitrogen atom and the alpha-carbon atom of the amino acid backbone. This creates a cyclic
structure that restricts the phi (Φ) angle rotation in a polypeptide chain. As a result, proline
acts as a ‘helix breaker’ and is often found in turns or the ends of alpha helices.
4. A reaction has a ΔH of -20 kJ/mol and a ΔS of -50 J/mol·K. At what temperature (in Kelvin)
does the reaction become non-spontaneous?
A. Below 200 K
B. Above 200 K
C. Above 400 K
D. Below 400 K
Answer: C
Explanation: Spontaneity is determined by the Gibbs free energy equation, ΔG = ΔH - TΔS.
For the reaction to be spontaneous, ΔG must be negative. Setting ΔG to zero (equilibrium)
and solving for T: 0 = -20,000 J/mol - T(-50 J/mol·K) gives T = 400 K. Since both enthalpy
and entropy are negative, the reaction is spontaneous at low temperatures and becomes
non-spontaneous above 400 K.
5. Which of the following amino acids would most likely be found in the interior of a globular
protein?
A. Aspartic Acid
B. Isoleucine
C. Lysine
D. Serine
Answer: B
Explanation: Globular proteins typically sequester hydrophobic side chains in their core to
avoid contact with the aqueous environment. Isoleucine has a nonpolar, branched
hydrocarbon side chain, making it highly hydrophobic. In contrast, Aspartic Acid, Lysine,
and Serine are polar or charged and are usually found on the surface interacting with
water.
6. The peptide bond is characterized by which of the following features?
A. Partial double-bond character
B. Free rotation around the C-N bond
C. A non-planar geometry
, D. Preferential cis configuration of side chains
Answer: A
Explanation: The peptide bond results from a resonance hybrid between the carbonyl
oxygen and the amide nitrogen. This resonance gives the C-N bond partial double-bond
character, which prevents rotation around that bond. Consequently, the six atoms involved
in the peptide group are coplanar, usually in the more stable trans configuration.
7. What is the net charge of the peptide Asp-Glu-Gly-Lys at pH 7.0?
A. -1
B. 0
C. +1
D. -2
Answer: A
Explanation: At pH 7.0, the N-terminus is +1 and the C-terminus is -1. The side chains of
Aspartic acid (Asp) and Glutamic acid (Glu) are both negatively charged (-1 each), while
Glycine is neutral and Lysine is positively charged (+1). Summing these charges: (+1) + (-1)
+ (-1) + 0 + (+1) + (-1) equals -1.
8. In an alpha helix, the hydrogen bonds occur between:
A. Carbonyl oxygen of residue n and amide hydrogen of residue n+4
B. Side chain atoms of amino acids three residues apart
C. Amide hydrogen of residue n and carbonyl oxygen of residue n+3
D. Carbonyl oxygen of residue n and amide hydrogen of residue n+1
Answer: A
Explanation: The alpha helix is stabilized by intrachain hydrogen bonds between the
backbone atoms. Specifically, the C=O group of the i-th residue forms a hydrogen bond with
the N-H group of the (i+4)-th residue. This specific spacing allows the helix to complete one
turn every 3.6 residues.
9. Which technique is most appropriate for determining the molecular weight of a protein
under denaturing conditions?
A. Gel filtration chromatography
B. SDS-PAGE
C. Ion exchange chromatography
D. Isoelectric focusing
Rationale (BCH4053 Exam 1) | University of Central Florida
1. Which of the following properties of water is primarily responsible for the hydrophobic
effect seen in protein folding?
A. High dielectric constant
B. Ability to form four hydrogen bonds
C. Tendency to maximize entropy by excluding nonpolar solutes
D. High specific heat capacity
Answer: C
Explanation: The hydrophobic effect is driven by the increase in entropy of water
molecules when nonpolar surfaces aggregate. When nonpolar molecules are separate,
water forms highly ordered clathrate cages around them, which is entropically unfavorable.
By clustering the nonpolar molecules, the total surface area decreases, releasing water
molecules into the bulk solvent and increasing the overall entropy of the system.
2. If a buffer solution has a pH of 7.4 and the pKa of the acid component is 6.8, what is the
ratio of [A-] to [HA]?
A. 1:1
B. 2:1
C. 10:1
D. 4:1
Answer: D
Explanation: Using the Henderson-Hasselbalch equation (pH = pKa + log([A-]/[HA])), we
substitute the given values: 7.4 = 6.8 + log([A-]/[HA]). This simplifies to 0.6 = log([A-
]/[HA]). Calculating the antilog (10^0.6) gives approximately 3.98, which rounds to a ratio
of 4:1.
3. Which amino acid contains a secondary amine within its structure, leading to significant
conformational constraints?
A. Histidine
B. Tryptophan
C. Glycine
D. Proline
,Answer: D
Explanation: Proline is unique because its side chain is covalently bonded to both the
nitrogen atom and the alpha-carbon atom of the amino acid backbone. This creates a cyclic
structure that restricts the phi (Φ) angle rotation in a polypeptide chain. As a result, proline
acts as a ‘helix breaker’ and is often found in turns or the ends of alpha helices.
4. A reaction has a ΔH of -20 kJ/mol and a ΔS of -50 J/mol·K. At what temperature (in Kelvin)
does the reaction become non-spontaneous?
A. Below 200 K
B. Above 200 K
C. Above 400 K
D. Below 400 K
Answer: C
Explanation: Spontaneity is determined by the Gibbs free energy equation, ΔG = ΔH - TΔS.
For the reaction to be spontaneous, ΔG must be negative. Setting ΔG to zero (equilibrium)
and solving for T: 0 = -20,000 J/mol - T(-50 J/mol·K) gives T = 400 K. Since both enthalpy
and entropy are negative, the reaction is spontaneous at low temperatures and becomes
non-spontaneous above 400 K.
5. Which of the following amino acids would most likely be found in the interior of a globular
protein?
A. Aspartic Acid
B. Isoleucine
C. Lysine
D. Serine
Answer: B
Explanation: Globular proteins typically sequester hydrophobic side chains in their core to
avoid contact with the aqueous environment. Isoleucine has a nonpolar, branched
hydrocarbon side chain, making it highly hydrophobic. In contrast, Aspartic Acid, Lysine,
and Serine are polar or charged and are usually found on the surface interacting with
water.
6. The peptide bond is characterized by which of the following features?
A. Partial double-bond character
B. Free rotation around the C-N bond
C. A non-planar geometry
, D. Preferential cis configuration of side chains
Answer: A
Explanation: The peptide bond results from a resonance hybrid between the carbonyl
oxygen and the amide nitrogen. This resonance gives the C-N bond partial double-bond
character, which prevents rotation around that bond. Consequently, the six atoms involved
in the peptide group are coplanar, usually in the more stable trans configuration.
7. What is the net charge of the peptide Asp-Glu-Gly-Lys at pH 7.0?
A. -1
B. 0
C. +1
D. -2
Answer: A
Explanation: At pH 7.0, the N-terminus is +1 and the C-terminus is -1. The side chains of
Aspartic acid (Asp) and Glutamic acid (Glu) are both negatively charged (-1 each), while
Glycine is neutral and Lysine is positively charged (+1). Summing these charges: (+1) + (-1)
+ (-1) + 0 + (+1) + (-1) equals -1.
8. In an alpha helix, the hydrogen bonds occur between:
A. Carbonyl oxygen of residue n and amide hydrogen of residue n+4
B. Side chain atoms of amino acids three residues apart
C. Amide hydrogen of residue n and carbonyl oxygen of residue n+3
D. Carbonyl oxygen of residue n and amide hydrogen of residue n+1
Answer: A
Explanation: The alpha helix is stabilized by intrachain hydrogen bonds between the
backbone atoms. Specifically, the C=O group of the i-th residue forms a hydrogen bond with
the N-H group of the (i+4)-th residue. This specific spacing allows the helix to complete one
turn every 3.6 residues.
9. Which technique is most appropriate for determining the molecular weight of a protein
under denaturing conditions?
A. Gel filtration chromatography
B. SDS-PAGE
C. Ion exchange chromatography
D. Isoelectric focusing
