CHEM210 Biochemistry
Final Assessment Review
Module 3 (Questions & Solutions)
2025
©2025
, 1. Case Study – Amino Acid Chirality:
A researcher isolates a novel amino acid from a marine microorganism
and determines that, unlike most amino acids, it does not have a chiral
center.
Question: Which amino acid is most likely observed?
A. Alanine
B. Leucine
C. Glycine
D. Serine
ANS: C. Glycine
Rationale: Glycine is unique among the standard amino acids because
its side chain is a single hydrogen atom, making it achiral. This lack of
stereocenter distinguishes it from all other α‑amino acids.
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2. Case Study – Zwitterion Formation:
In a pH titration experiment, a student finds that at physiological pH,
amino acids exist predominantly as zwitterions.
Question: What best describes a zwitterion?
A. A molecule with only negative charges
B. A molecule with only positive charges
C. A molecule with both a positively charged amino group and a
negatively charged carboxyl group
D. A molecule with no net charge due to covalent bonding
ANS: C. A molecule with both a positively charged amino group and a
negatively charged carboxyl group
Rationale: At intermediate pH values, especially around physiological
pH, amino acids exist as zwitterions with a protonated (–NH₃⁺) amino
group and a deprotonated (–COO⁻) carboxyl group, leading to overall
electrical neutrality with internal charges.
©2025
, ---
3. Case Study – Peptide Bond Characteristics:
During a structural study, a biochemist observes that peptide bonds show
a high degree of planarity.
Question: What is the primary reason for the planarity of peptide
bonds?
A. The double-bond character from resonance
B. The steric hindrance of side chains
C. The flexibility of the alpha carbon
D. Solvent interactions with the peptide backbone
ANS: A. The double-bond character from resonance
Rationale: Resonance between the carbonyl group (C=O) and the
amide nitrogen imparts partial double-bond character to the peptide
bond, limiting rotation and enforcing planarity.
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4. Case Study – Protein Secondary Structure:
Using circular dichroism (CD) spectroscopy, a student finds two
characteristic minima at 208 nm and 222 nm for a purified protein
sample.
Question: What secondary structure is most consistent with these CD
spectral features?
A. Beta sheet
B. Random coil
C. Alpha helix
D. Beta turn
ANS: C. Alpha helix
Rationale: CD spectra with double minima near 208 and 222 nm are
indicative of significant α‑helical content in proteins. These features arise
due to the regular arrangement of dipoles in the helix.
©2025
Final Assessment Review
Module 3 (Questions & Solutions)
2025
©2025
, 1. Case Study – Amino Acid Chirality:
A researcher isolates a novel amino acid from a marine microorganism
and determines that, unlike most amino acids, it does not have a chiral
center.
Question: Which amino acid is most likely observed?
A. Alanine
B. Leucine
C. Glycine
D. Serine
ANS: C. Glycine
Rationale: Glycine is unique among the standard amino acids because
its side chain is a single hydrogen atom, making it achiral. This lack of
stereocenter distinguishes it from all other α‑amino acids.
---
2. Case Study – Zwitterion Formation:
In a pH titration experiment, a student finds that at physiological pH,
amino acids exist predominantly as zwitterions.
Question: What best describes a zwitterion?
A. A molecule with only negative charges
B. A molecule with only positive charges
C. A molecule with both a positively charged amino group and a
negatively charged carboxyl group
D. A molecule with no net charge due to covalent bonding
ANS: C. A molecule with both a positively charged amino group and a
negatively charged carboxyl group
Rationale: At intermediate pH values, especially around physiological
pH, amino acids exist as zwitterions with a protonated (–NH₃⁺) amino
group and a deprotonated (–COO⁻) carboxyl group, leading to overall
electrical neutrality with internal charges.
©2025
, ---
3. Case Study – Peptide Bond Characteristics:
During a structural study, a biochemist observes that peptide bonds show
a high degree of planarity.
Question: What is the primary reason for the planarity of peptide
bonds?
A. The double-bond character from resonance
B. The steric hindrance of side chains
C. The flexibility of the alpha carbon
D. Solvent interactions with the peptide backbone
ANS: A. The double-bond character from resonance
Rationale: Resonance between the carbonyl group (C=O) and the
amide nitrogen imparts partial double-bond character to the peptide
bond, limiting rotation and enforcing planarity.
---
4. Case Study – Protein Secondary Structure:
Using circular dichroism (CD) spectroscopy, a student finds two
characteristic minima at 208 nm and 222 nm for a purified protein
sample.
Question: What secondary structure is most consistent with these CD
spectral features?
A. Beta sheet
B. Random coil
C. Alpha helix
D. Beta turn
ANS: C. Alpha helix
Rationale: CD spectra with double minima near 208 and 222 nm are
indicative of significant α‑helical content in proteins. These features arise
due to the regular arrangement of dipoles in the helix.
©2025
