BCH 4053 Exam 1 V2 | BCH 4053 Biochemistry I | Actual Q&A with
Rationale (BCH4053 Exam 1) | University of Central Florida
1. Which of the following thermodynamic terms describes the degree of disorder or
randomness in a biochemical system?
A. Enthalpy
B. Entropy
C. Gibbs Free Energy
D. Chemical Potential
Answer: B
Explanation: Entropy is a measure of the disorder or randomness within a system. In
biochemical reactions, an increase in entropy often drives processes like protein folding
and the formation of lipid bilayers. The second law of thermodynamics states that the total
entropy of an isolated system always increases over time.
2. In a water molecule, the bond angle between the two hydrogen atoms is approximately:
A. 180 degrees
B. 90 degrees
C. 104.5 degrees
D. 120 degrees
Answer: C
Explanation: The water molecule has a bent geometry due to the two lone pairs of
electrons on the oxygen atom. These lone pairs exert greater repulsive forces than the
bonding pairs, pushing the hydrogen atoms closer together. This resulting 104.5 degree
angle is slightly less than the ideal tetrahedral angle of 109.5 degrees.
3. Which type of non-covalent interaction is primarily responsible for the ‘hydrophobic effect’
in protein folding?
A. Entropy-driven exclusion of water molecules
B. Strong hydrogen bonding between non-polar side chains
C. Ionic interactions between leucine and valine
D. Covalent linkage of methyl groups
Answer: A
,Explanation: The hydrophobic effect is driven by the release of water molecules from a
highly ordered clathrate cage structure surrounding non-polar solutes. When non-polar
groups aggregate, the total surface area decreases, releasing water and increasing the
entropy of the solvent. This increase in solvent entropy makes the association of non-polar
groups energetically favorable.
4. What is the pH of a solution with a hydrogen ion concentration [H+] of 1.0 x 10^-4 M?
A. 4
B. 7
C. 10
D. 14
Answer: A
Explanation: The pH is defined as the negative logarithm (base 10) of the hydrogen ion
concentration. Using the formula pH = -log[H+], we calculate -log(1.0 x 10^-4), which
equals 4. A pH of 4 indicates an acidic solution common in various biochemical
experimental buffers.
5. According to the Henderson-Hasselbalch equation, when the pH of a solution equals the
pKa of the weak acid, the ratio of [A-] to [HA] is:
A. 100
B. 10
C. 0.1
D. 1
Answer: D
Explanation: The Henderson-Hasselbalch equation is pH = pKa + log([A-]/[HA]). If pH =
pKa, then log([A-]/[HA]) must be zero. Since the log of 1 is zero, the concentration of the
conjugate base [A-] must equal the concentration of the weak acid [HA].
6. Which of the following amino acids contains a side chain capable of forming a disulfide
bond?
A. Methionine
B. Serine
C. Cysteine
D. Alanine
Answer: C
, Explanation: Cysteine contains a reactive thiol (-SH) group in its side chain. Two cysteine
residues can undergo oxidation to form a covalent disulfide bridge (-S-S-), which is vital for
stabilizing the tertiary and quaternary structures of many extracellular proteins.
Methionine also contains sulfur but in the form of a thioether, which cannot form disulfide
bonds.
7. Which amino acid is classified as ‘achiral’ because its R-group is a single hydrogen atom?
A. Proline
B. Alanine
C. Glycine
D. Valine
Answer: C
Explanation: Glycine is the simplest amino acid and is unique because it is the only one
without a chiral alpha-carbon. Its side chain is a hydrogen atom, making it identical to the
hydrogen already attached to the alpha-carbon. This lack of chirality allows glycine to fit
into tight spaces in protein structures, such as the triple helix of collagen.
8. In the peptide bond, which two atoms are involved in the covalent linkage between amino
acids?
A. The alpha-carbon of one and the R-group of another
B. The carbonyl carbon of one and the amino nitrogen of another
C. Two alpha-carbons
D. The nitrogen of the R-group and the carboxyl oxygen
Answer: B
Explanation: A peptide bond is formed through a dehydration reaction between the
carboxyl group of one amino acid and the amino group of the next. The resulting C-N bond
has partial double-bond character due to resonance, which restricts rotation. This planarity
is a fundamental constraint in the folding of polypeptide chains.
9. The pH at which a molecule has a net charge of zero is known as its:
A. Isoelectric point (pI)
B. pKb
C. pKa
D. Equivalence point
Answer: A
Rationale (BCH4053 Exam 1) | University of Central Florida
1. Which of the following thermodynamic terms describes the degree of disorder or
randomness in a biochemical system?
A. Enthalpy
B. Entropy
C. Gibbs Free Energy
D. Chemical Potential
Answer: B
Explanation: Entropy is a measure of the disorder or randomness within a system. In
biochemical reactions, an increase in entropy often drives processes like protein folding
and the formation of lipid bilayers. The second law of thermodynamics states that the total
entropy of an isolated system always increases over time.
2. In a water molecule, the bond angle between the two hydrogen atoms is approximately:
A. 180 degrees
B. 90 degrees
C. 104.5 degrees
D. 120 degrees
Answer: C
Explanation: The water molecule has a bent geometry due to the two lone pairs of
electrons on the oxygen atom. These lone pairs exert greater repulsive forces than the
bonding pairs, pushing the hydrogen atoms closer together. This resulting 104.5 degree
angle is slightly less than the ideal tetrahedral angle of 109.5 degrees.
3. Which type of non-covalent interaction is primarily responsible for the ‘hydrophobic effect’
in protein folding?
A. Entropy-driven exclusion of water molecules
B. Strong hydrogen bonding between non-polar side chains
C. Ionic interactions between leucine and valine
D. Covalent linkage of methyl groups
Answer: A
,Explanation: The hydrophobic effect is driven by the release of water molecules from a
highly ordered clathrate cage structure surrounding non-polar solutes. When non-polar
groups aggregate, the total surface area decreases, releasing water and increasing the
entropy of the solvent. This increase in solvent entropy makes the association of non-polar
groups energetically favorable.
4. What is the pH of a solution with a hydrogen ion concentration [H+] of 1.0 x 10^-4 M?
A. 4
B. 7
C. 10
D. 14
Answer: A
Explanation: The pH is defined as the negative logarithm (base 10) of the hydrogen ion
concentration. Using the formula pH = -log[H+], we calculate -log(1.0 x 10^-4), which
equals 4. A pH of 4 indicates an acidic solution common in various biochemical
experimental buffers.
5. According to the Henderson-Hasselbalch equation, when the pH of a solution equals the
pKa of the weak acid, the ratio of [A-] to [HA] is:
A. 100
B. 10
C. 0.1
D. 1
Answer: D
Explanation: The Henderson-Hasselbalch equation is pH = pKa + log([A-]/[HA]). If pH =
pKa, then log([A-]/[HA]) must be zero. Since the log of 1 is zero, the concentration of the
conjugate base [A-] must equal the concentration of the weak acid [HA].
6. Which of the following amino acids contains a side chain capable of forming a disulfide
bond?
A. Methionine
B. Serine
C. Cysteine
D. Alanine
Answer: C
, Explanation: Cysteine contains a reactive thiol (-SH) group in its side chain. Two cysteine
residues can undergo oxidation to form a covalent disulfide bridge (-S-S-), which is vital for
stabilizing the tertiary and quaternary structures of many extracellular proteins.
Methionine also contains sulfur but in the form of a thioether, which cannot form disulfide
bonds.
7. Which amino acid is classified as ‘achiral’ because its R-group is a single hydrogen atom?
A. Proline
B. Alanine
C. Glycine
D. Valine
Answer: C
Explanation: Glycine is the simplest amino acid and is unique because it is the only one
without a chiral alpha-carbon. Its side chain is a hydrogen atom, making it identical to the
hydrogen already attached to the alpha-carbon. This lack of chirality allows glycine to fit
into tight spaces in protein structures, such as the triple helix of collagen.
8. In the peptide bond, which two atoms are involved in the covalent linkage between amino
acids?
A. The alpha-carbon of one and the R-group of another
B. The carbonyl carbon of one and the amino nitrogen of another
C. Two alpha-carbons
D. The nitrogen of the R-group and the carboxyl oxygen
Answer: B
Explanation: A peptide bond is formed through a dehydration reaction between the
carboxyl group of one amino acid and the amino group of the next. The resulting C-N bond
has partial double-bond character due to resonance, which restricts rotation. This planarity
is a fundamental constraint in the folding of polypeptide chains.
9. The pH at which a molecule has a net charge of zero is known as its:
A. Isoelectric point (pI)
B. pKb
C. pKa
D. Equivalence point
Answer: A
