BCH 4053 Exam 1 V1 | 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 its ability to dissolve
a wide variety of polar substances?
A. Its high specific heat capacity
B. Its ability to form covalent bonds with solutes
C. Its high dielectric constant
D. Its low molar mass
Answer: C
Explanation: Water has a high dielectric constant, which reduces the attractive forces
between oppositely charged ions in a salt. This property allows water to effectively screen
charges and hydrate ions, leading to dissolution. The ability of water to surround ions with
a hydration shell is a fundamental aspect of biochemical solubility.
2. If the pH of a solution is 4.5, what is the concentration of hydroxide ions [OH-]? (Assume 25
degrees Celsius)
A. 3.16 x 10^-5 M
B. 4.5 x 10^-10 M
C. 1.0 x 10^-7 M
D. 3.16 x 10^-10 M
Answer: D
Explanation: The sum of pH and pOH is always 14 at standard biological temperatures.
Since the pH is 4.5, the pOH must be 9.5. Calculating the inverse log of -9.5 gives a
hydroxide concentration of approximately 3.16 x 10^-10 M.
3. Which amino acid contains a thioether functional group in its side chain?
A. Cysteine
B. Methionine
C. Serine
D. Threonine
Answer: B
,Explanation: Methionine features a sulfur atom bonded to two carbon atoms, which
defines the thioether functional group. Cysteine, by contrast, contains a sulfhydryl (-SH)
group that is capable of forming disulfide bridges. Understanding these specific side chain
chemistries is essential for predicting protein folding and stability.
4. Under what condition is the Henderson-Hasselbalch equation most accurate for
determining the pH of a buffer solution?
A. When the concentration of the acid is ten times the base
B. When the pH is far from the pKa
C. When the concentrations of the conjugate acid and base are relatively high and within a
1:10 ratio
D. When the solution is extremely dilute
Answer: C
Explanation: The Henderson-Hasselbalch equation assumes that the equilibrium
concentrations of the acid and base are approximately equal to their initial concentrations.
This approximation holds best when the concentrations are high enough to resist small
changes from water dissociation. Additionally, buffers are most effective when the pH is
within one unit of the pKa.
5. In a Ramachandran plot, the values of which two angles are plotted to show allowed
protein conformations?
A. Phi and Psi
B. Alpha and Beta
C. Omega and Epsilon
D. Sigma and Pi
Answer: A
Explanation: The Ramachandran plot tracks the torsion angles of the polypeptide
backbone, specifically Phi (between N and Alpha-C) and Psi (between Alpha-C and
Carbonyl-C). Certain combinations of these angles are sterically forbidden due to clashes
between atoms. This tool is vital for validating the structural quality of protein models
obtained via X-ray crystallography.
6. Which of the following thermodynamic parameters must be negative for a reaction to be
considered spontaneous?
A. Gibbs Free Energy (G)
B. Entropy (S)
C. Enthalpy (H)
, D. Temperature (T)
Answer: A
Explanation: A negative change in Gibbs Free Energy (delta G) indicates that a process can
occur without the input of external energy. This spontaneity depends on both the enthalpy
change and the entropy change of the system. In biochemistry, non-spontaneous reactions
are often coupled with ATP hydrolysis to drive them forward.
7. The ‘Hydrophobic Effect’ is primarily driven by which factor?
A. Strong van der Waals forces between nonpolar molecules
B. Hydrogen bonding between the lipid tails
C. An increase in the entropy of water molecules
D. The electronegativity of carbon
Answer: C
Explanation: When nonpolar substances aggregate, the ordered ‘clathrate’ cages of water
molecules around them are disrupted. This release of water molecules into the bulk solvent
significantly increases the entropy of the system. This entropic gain is the primary
thermodynamic force behind protein folding and membrane formation.
8. What is the net charge of the amino acid Glutamate at pH 7.0?
A. +1
B. 0
C. -2
D. -1
Answer: D
Explanation: Glutamate has three ionizable groups: the alpha-carboxyl (pKa ~2), the
alpha-amino (pKa ~9.5), and the side chain carboxyl (pKa ~4.2). At pH 7, the alpha-
carboxyl is deprotonated (-1), the alpha-amino is protonated (+1), and the side chain is
deprotonated (-1). Adding these gives a net charge of -1.
9. Which reagent is commonly used to sequence a polypeptide from the N-terminus by
labeling and cleaving the first residue?
A. Phenylisothiocyanate (PITC)
B. Cyanogen Bromide
C. Trypsin
D. Beta-mercaptoethanol
Rationale (BCH4053 Exam 1) | University of Central Florida
1. Which of the following properties of water is primarily responsible for its ability to dissolve
a wide variety of polar substances?
A. Its high specific heat capacity
B. Its ability to form covalent bonds with solutes
C. Its high dielectric constant
D. Its low molar mass
Answer: C
Explanation: Water has a high dielectric constant, which reduces the attractive forces
between oppositely charged ions in a salt. This property allows water to effectively screen
charges and hydrate ions, leading to dissolution. The ability of water to surround ions with
a hydration shell is a fundamental aspect of biochemical solubility.
2. If the pH of a solution is 4.5, what is the concentration of hydroxide ions [OH-]? (Assume 25
degrees Celsius)
A. 3.16 x 10^-5 M
B. 4.5 x 10^-10 M
C. 1.0 x 10^-7 M
D. 3.16 x 10^-10 M
Answer: D
Explanation: The sum of pH and pOH is always 14 at standard biological temperatures.
Since the pH is 4.5, the pOH must be 9.5. Calculating the inverse log of -9.5 gives a
hydroxide concentration of approximately 3.16 x 10^-10 M.
3. Which amino acid contains a thioether functional group in its side chain?
A. Cysteine
B. Methionine
C. Serine
D. Threonine
Answer: B
,Explanation: Methionine features a sulfur atom bonded to two carbon atoms, which
defines the thioether functional group. Cysteine, by contrast, contains a sulfhydryl (-SH)
group that is capable of forming disulfide bridges. Understanding these specific side chain
chemistries is essential for predicting protein folding and stability.
4. Under what condition is the Henderson-Hasselbalch equation most accurate for
determining the pH of a buffer solution?
A. When the concentration of the acid is ten times the base
B. When the pH is far from the pKa
C. When the concentrations of the conjugate acid and base are relatively high and within a
1:10 ratio
D. When the solution is extremely dilute
Answer: C
Explanation: The Henderson-Hasselbalch equation assumes that the equilibrium
concentrations of the acid and base are approximately equal to their initial concentrations.
This approximation holds best when the concentrations are high enough to resist small
changes from water dissociation. Additionally, buffers are most effective when the pH is
within one unit of the pKa.
5. In a Ramachandran plot, the values of which two angles are plotted to show allowed
protein conformations?
A. Phi and Psi
B. Alpha and Beta
C. Omega and Epsilon
D. Sigma and Pi
Answer: A
Explanation: The Ramachandran plot tracks the torsion angles of the polypeptide
backbone, specifically Phi (between N and Alpha-C) and Psi (between Alpha-C and
Carbonyl-C). Certain combinations of these angles are sterically forbidden due to clashes
between atoms. This tool is vital for validating the structural quality of protein models
obtained via X-ray crystallography.
6. Which of the following thermodynamic parameters must be negative for a reaction to be
considered spontaneous?
A. Gibbs Free Energy (G)
B. Entropy (S)
C. Enthalpy (H)
, D. Temperature (T)
Answer: A
Explanation: A negative change in Gibbs Free Energy (delta G) indicates that a process can
occur without the input of external energy. This spontaneity depends on both the enthalpy
change and the entropy change of the system. In biochemistry, non-spontaneous reactions
are often coupled with ATP hydrolysis to drive them forward.
7. The ‘Hydrophobic Effect’ is primarily driven by which factor?
A. Strong van der Waals forces between nonpolar molecules
B. Hydrogen bonding between the lipid tails
C. An increase in the entropy of water molecules
D. The electronegativity of carbon
Answer: C
Explanation: When nonpolar substances aggregate, the ordered ‘clathrate’ cages of water
molecules around them are disrupted. This release of water molecules into the bulk solvent
significantly increases the entropy of the system. This entropic gain is the primary
thermodynamic force behind protein folding and membrane formation.
8. What is the net charge of the amino acid Glutamate at pH 7.0?
A. +1
B. 0
C. -2
D. -1
Answer: D
Explanation: Glutamate has three ionizable groups: the alpha-carboxyl (pKa ~2), the
alpha-amino (pKa ~9.5), and the side chain carboxyl (pKa ~4.2). At pH 7, the alpha-
carboxyl is deprotonated (-1), the alpha-amino is protonated (+1), and the side chain is
deprotonated (-1). Adding these gives a net charge of -1.
9. Which reagent is commonly used to sequence a polypeptide from the N-terminus by
labeling and cleaving the first residue?
A. Phenylisothiocyanate (PITC)
B. Cyanogen Bromide
C. Trypsin
D. Beta-mercaptoethanol
