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AMERICAN CHEMICAL SOCIETY (ACS)
BIOCHEMISTRY 2026 EXAM COMPLETE (100)
CURRENT TESTING QUESTIONS AND
CORRECT ANSWERS WITH DETAILED
EXPLANATIONS|GUARANTEED PASS.
ACS
Prepare with confidence using this American Chemical Society (ACS)
Biochemistry Exam, designed to assess core knowledge of
biochemical principles and molecular processes. It focuses on
amino acids, protein structure, enzyme kinetics, metabolism,
nucleic acids, gene expression, signaling, and common biochemical
techniques. Suitable for chemistry, biochemistry, and pre-health
students preparing for ACS standardized examinations.
MULTIPLE CHOICE.
Amino Acids & Protein Primary Structure (1–10)
1. Which amino acid has a side chain that contains an indole
ring?
A) Phenylalanine
B) Tyrosine
C) Tryptophan
D) Histidine
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Answer: C. Tryptophan
Explanation: Tryptophan’s side chain includes an indole
group (benzene fused to pyrrole), making it the most
UV-absorbing amino acid near 280 nm.
2. The peptide bond is best described as:
A) Fully flexible and rotatable
B) Partial double bond character due to resonance, restricting
rotation
C) An ester linkage
D) Only found in cyclic peptides
Answer: B. Partial double bond character due to resonance,
restricting rotation
Explanation: Resonance between the carbonyl oxygen and
nitrogen gives the peptide bond ~40% double bond
character, making it planar and rigid.
3. Which amino acid is optically inactive?
A) Alanine
B) Glycine
C) Leucine
D) Proline
Answer: B. Glycine
Explanation: Glycine has two hydrogens on the α-carbon, so
it is not chiral and has no optical activity.
4. At physiological pH (~7.4), the side chain of lysine is
typically:
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A) Neutral
B) Positively charged
C) Negatively charged
D) Hydrophobic
Answer: B. Positively charged
Explanation: Lysine has an amino group (pKa ≈ 10.5) that is
protonated and positively charged at pH 7.4.
5. Which of the following amino acids contains a thiol group
that can form disulfide bonds?
A) Methionine
B) Serine
C) Cysteine
D) Threonine
Answer: C. Cysteine
Explanation: Cysteine’s side chain is –CH₂–SH. Two
cysteines can oxidize to form a disulfide bridge (cystine).
6. The isoelectric point (pI) of a protein is the pH at which:
A) The protein has maximum solubility
B) The net charge of the protein is zero
C) The protein denatures
D) The protein has maximum catalytic activity
Answer: B. The net charge of the protein is zero
Explanation: At the pI, the number of positive and negative
charges are equal; protein may precipitate due to lack of
electrostatic repulsion.
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7. Which of the following amino acids has a side chain that is
aromatic and can be phosphorylated?
A) Phenylalanine
B) Tyrosine
C) Tryptophan
D) Histidine
Answer: B. Tyrosine
Explanation: Tyrosine has a phenolic –OH that can be
phosphorylated by protein tyrosine kinases, a key signaling
modification.
8. Edman degradation is used to:
A) Cleave disulfide bonds
B) Determine the N-terminal amino acid sequence of a protein
C) Measure protein molecular weight
D) Digest proteins into small peptides
Answer: B. Determine the N-terminal amino acid sequence
of a protein
Explanation: Edman degradation sequentially removes
N-terminal residues as PTH-amino acids, allowing
identification.
9. Which amino acid introduces a kink or turn in a
polypeptide chain due to its cyclic structure?
A) Glycine
B) Proline
AMERICAN CHEMICAL SOCIETY (ACS)
BIOCHEMISTRY 2026 EXAM COMPLETE (100)
CURRENT TESTING QUESTIONS AND
CORRECT ANSWERS WITH DETAILED
EXPLANATIONS|GUARANTEED PASS.
ACS
Prepare with confidence using this American Chemical Society (ACS)
Biochemistry Exam, designed to assess core knowledge of
biochemical principles and molecular processes. It focuses on
amino acids, protein structure, enzyme kinetics, metabolism,
nucleic acids, gene expression, signaling, and common biochemical
techniques. Suitable for chemistry, biochemistry, and pre-health
students preparing for ACS standardized examinations.
MULTIPLE CHOICE.
Amino Acids & Protein Primary Structure (1–10)
1. Which amino acid has a side chain that contains an indole
ring?
A) Phenylalanine
B) Tyrosine
C) Tryptophan
D) Histidine
, Page 2 of 44
Answer: C. Tryptophan
Explanation: Tryptophan’s side chain includes an indole
group (benzene fused to pyrrole), making it the most
UV-absorbing amino acid near 280 nm.
2. The peptide bond is best described as:
A) Fully flexible and rotatable
B) Partial double bond character due to resonance, restricting
rotation
C) An ester linkage
D) Only found in cyclic peptides
Answer: B. Partial double bond character due to resonance,
restricting rotation
Explanation: Resonance between the carbonyl oxygen and
nitrogen gives the peptide bond ~40% double bond
character, making it planar and rigid.
3. Which amino acid is optically inactive?
A) Alanine
B) Glycine
C) Leucine
D) Proline
Answer: B. Glycine
Explanation: Glycine has two hydrogens on the α-carbon, so
it is not chiral and has no optical activity.
4. At physiological pH (~7.4), the side chain of lysine is
typically:
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A) Neutral
B) Positively charged
C) Negatively charged
D) Hydrophobic
Answer: B. Positively charged
Explanation: Lysine has an amino group (pKa ≈ 10.5) that is
protonated and positively charged at pH 7.4.
5. Which of the following amino acids contains a thiol group
that can form disulfide bonds?
A) Methionine
B) Serine
C) Cysteine
D) Threonine
Answer: C. Cysteine
Explanation: Cysteine’s side chain is –CH₂–SH. Two
cysteines can oxidize to form a disulfide bridge (cystine).
6. The isoelectric point (pI) of a protein is the pH at which:
A) The protein has maximum solubility
B) The net charge of the protein is zero
C) The protein denatures
D) The protein has maximum catalytic activity
Answer: B. The net charge of the protein is zero
Explanation: At the pI, the number of positive and negative
charges are equal; protein may precipitate due to lack of
electrostatic repulsion.
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7. Which of the following amino acids has a side chain that is
aromatic and can be phosphorylated?
A) Phenylalanine
B) Tyrosine
C) Tryptophan
D) Histidine
Answer: B. Tyrosine
Explanation: Tyrosine has a phenolic –OH that can be
phosphorylated by protein tyrosine kinases, a key signaling
modification.
8. Edman degradation is used to:
A) Cleave disulfide bonds
B) Determine the N-terminal amino acid sequence of a protein
C) Measure protein molecular weight
D) Digest proteins into small peptides
Answer: B. Determine the N-terminal amino acid sequence
of a protein
Explanation: Edman degradation sequentially removes
N-terminal residues as PTH-amino acids, allowing
identification.
9. Which amino acid introduces a kink or turn in a
polypeptide chain due to its cyclic structure?
A) Glycine
B) Proline
