CHEM 153A Midterm 1 Exam | Questions
and Solutions
Fall 2026/2027 Update Complete – UCLA
Biochemistry: Macromolecular Structure & Protein Function | Key Domains: Amino Acids,
Protein Structure, Protein Folding, Hemoglobin/Myoglobin, Protein Techniques, Enzyme
Introduction
Introduction: This structured CHEM 153A Midterm 1 Exam for UCLA provides 55 high-quality,
exam-style questions with verified correct answers and detailed rationales for the Fall 2026/2027
term. Content emphasizes amino acid chemistry, protein structure hierarchy, folding forces, oxygen
binding kinetics, and foundational biochemical techniques.
Exam Structure: Midterm 1 Exam (55 QUESTIONS)
Answer Format: Correct answers appear in bold cyan blue with rationales explaining structural
features, stabilizing forces, binding curves, or functional principles.
CHEM 153A Midterm 1 Exam – 55 Verified Questions
1. The peptide bond is:
A. Formed by a hydrolysis reaction
,B. A covalent bond with partial double-bond character
C. Freely rotatable
D. An ionic bond
B. A covalent bond with partial double-bond character
The peptide bond is a covalent amide linkage formed by dehydration synthesis. Resonance gives it
~40% double-bond character, making it planar and non-rotatable, which constrains protein
backbone conformation.
2. Which amino acid is achiral?
A. Alanine
B. Glycine
C. Serine
,D. Valine
B. Glycine
Glycine has two hydrogen atoms on its α-carbon, so it lacks a chiral center and is not optically
active. All other standard amino acids are L-isomers with four different α-substituents.
3. The primary structure of a protein is defined by:
A. Hydrogen bonding between backbone atoms
B. The sequence of amino acids linked by peptide bonds
C. Hydrophobic interactions among side chains
D. Disulfide bonds between cysteine residues
B. The sequence of amino acids linked by peptide bonds
, Primary structure is the linear covalent sequence of amino acids joined by peptide bonds. This
sequence dictates all higher levels of protein folding and function (Anfinsen's dogma).
4. Which force is most important in stabilizing the tertiary structure of a water-soluble
globular protein?
A. Peptide bonds
B. Hydrogen bonds
C. Hydrophobic interactions
D. Ionic bonds
C. Hydrophobic interactions
Hydrophobic side chains cluster in the protein interior to minimize contact with water, providing
the major driving force for tertiary folding. Hydrogen bonds and ionic interactions fine-tune the
structure.
5. In the α-helix, hydrogen bonds form between:
and Solutions
Fall 2026/2027 Update Complete – UCLA
Biochemistry: Macromolecular Structure & Protein Function | Key Domains: Amino Acids,
Protein Structure, Protein Folding, Hemoglobin/Myoglobin, Protein Techniques, Enzyme
Introduction
Introduction: This structured CHEM 153A Midterm 1 Exam for UCLA provides 55 high-quality,
exam-style questions with verified correct answers and detailed rationales for the Fall 2026/2027
term. Content emphasizes amino acid chemistry, protein structure hierarchy, folding forces, oxygen
binding kinetics, and foundational biochemical techniques.
Exam Structure: Midterm 1 Exam (55 QUESTIONS)
Answer Format: Correct answers appear in bold cyan blue with rationales explaining structural
features, stabilizing forces, binding curves, or functional principles.
CHEM 153A Midterm 1 Exam – 55 Verified Questions
1. The peptide bond is:
A. Formed by a hydrolysis reaction
,B. A covalent bond with partial double-bond character
C. Freely rotatable
D. An ionic bond
B. A covalent bond with partial double-bond character
The peptide bond is a covalent amide linkage formed by dehydration synthesis. Resonance gives it
~40% double-bond character, making it planar and non-rotatable, which constrains protein
backbone conformation.
2. Which amino acid is achiral?
A. Alanine
B. Glycine
C. Serine
,D. Valine
B. Glycine
Glycine has two hydrogen atoms on its α-carbon, so it lacks a chiral center and is not optically
active. All other standard amino acids are L-isomers with four different α-substituents.
3. The primary structure of a protein is defined by:
A. Hydrogen bonding between backbone atoms
B. The sequence of amino acids linked by peptide bonds
C. Hydrophobic interactions among side chains
D. Disulfide bonds between cysteine residues
B. The sequence of amino acids linked by peptide bonds
, Primary structure is the linear covalent sequence of amino acids joined by peptide bonds. This
sequence dictates all higher levels of protein folding and function (Anfinsen's dogma).
4. Which force is most important in stabilizing the tertiary structure of a water-soluble
globular protein?
A. Peptide bonds
B. Hydrogen bonds
C. Hydrophobic interactions
D. Ionic bonds
C. Hydrophobic interactions
Hydrophobic side chains cluster in the protein interior to minimize contact with water, providing
the major driving force for tertiary folding. Hydrogen bonds and ionic interactions fine-tune the
structure.
5. In the α-helix, hydrogen bonds form between:
