CHEM 210 BIOCHEMISTRY PRACTICE
MOCK TEST 250 QUESTIONS WITH
CORRECT ANSWERS AND RATIONALES
PORTAGE CHEM 210 – REAL TEST PREP
SECTION 1: AMINO ACIDS & PROTEIN STRUCTURE (Questions 1–40)
1. Which amino acid has a side chain that contains a primary amino group and is often involved
in cross-linking proteins?
A) Cysteine
B) Lysine
C) Glutamate
D) Proline
Answer: B
Rationale: Lysine contains a primary amine (–NH₂) in its side chain. It is often involved in
cross-linking proteins and in post-translational modifications such as acetylation and ubiquitination.
2. Which amino acid is the only one with a side chain that can form disulfide bonds?
A) Methionine
B) Cysteine
C) Serine
D) Threonine
Answer: B
Rationale: Cysteine contains a thiol (–SH) group that can oxidize to form a disulfide bond (–S–S–)
with another cysteine, stabilizing protein tertiary and quaternary structure.
3. Which level of protein structure refers to the linear sequence of amino acids?
A) Primary
B) Secondary
C) Tertiary
D) Quaternary
Answer: A
Rationale: The primary structure of a protein is the linear sequence of amino acids held together
by covalent peptide bonds.
4. Which secondary structure is stabilized by hydrogen bonds between the carbonyl oxygen of
one residue and the amide hydrogen of a residue four residues away?
A) α-helix
B) β-sheet
,C) β-turn
D) Random coil
Answer: A
*Rationale: The α-helix is a right-handed coil stabilized by hydrogen bonds between the carbonyl
oxygen of residue n and the amide hydrogen of residue n+4.*
5. Which of the following amino acids is often found in β-turns because of its rigid cyclic structure?
A) Glycine
B) Alanine
C) Proline
D) Valine
Answer: C
Rationale: Proline has a rigid cyclic structure that forces a kink in the polypeptide chain, making it
common in β-turns and loops.
6. The peptide bond has partial double-bond character due to resonance. What is the
consequence of this?
A) The bond is freely rotatable
B) The bond is planar and rigid
C) The bond is weaker than a single bond
D) The bond is ionic
Answer: B
Rationale: Resonance delocalization of the lone pair on the amide nitrogen gives the peptide
bond about 40% double-bond character, making it planar and rigid.
7. Which amino acid is often called a "helix breaker" because it disrupts α-helix regularity?
A) Alanine
B) Leucine
C) Proline
D) Valine
Answer: C
Rationale: Proline lacks an amide hydrogen to participate in helix hydrogen bonding and its rigid
ring structure introduces a kink, disrupting α-helix regularity.
8. The isoelectric point (pI) of an amino acid is the pH at which:
A) The amino acid has no charge
B) The amino acid has maximum positive charge
C) The amino acid has maximum negative charge
D) The amino acid is fully protonated
Answer: A
Rationale: At the isoelectric point, the net charge of the amino acid or protein is zero. It will not
migrate in an electric field.
,9. Which of the following amino acids has a side chain that contains an aromatic ring?
A) Methionine
B) Phenylalanine
C) Serine
D) Asparagine
Answer: B
Rationale: Phenylalanine has a benzyl side chain (aromatic ring). Other aromatic amino acids are
tyrosine and tryptophan.
10. Which amino acid is the precursor for the neurotransmitter serotonin?
A) Tyrosine
B) Tryptophan
C) Histidine
D) Glutamate
Answer: B
Rationale: Tryptophan is hydroxylated to 5-hydroxytryptophan, which is decarboxylated to
serotonin (5-hydroxytryptamine).
11. Which type of interaction is primarily responsible for stabilizing the hydrophobic core of a
protein?
A) Hydrogen bonds
B) Ionic bonds
C) Hydrophobic interactions
D) Disulfide bonds
Answer: C
Rationale: Nonpolar amino acid side chains cluster together in the protein interior to minimize
contact with water, driven by hydrophobic interactions.
12. How many standard amino acids are found in proteins?
A) 18
B) 20
C) 22
D) 24
Answer: B
Rationale: There are 20 standard (proteinogenic) amino acids encoded by the universal genetic
code.
13. The technique that separates proteins based on their isoelectric point is called:
A) SDS-PAGE
B) Western blotting
C) Isoelectric focusing
D) Size-exclusion chromatography
, Answer: C
Rationale: Isoelectric focusing separates proteins based on their isoelectric point (pI) in a pH
gradient under an electric field.
14. Which reagent is commonly used to reduce disulfide bonds in proteins?
A) Urea
B) SDS
C) β-Mercaptoethanol
D) Coomassie blue
Answer: C
Rationale: β-Mercaptoethanol (and dithiothreitol, DTT) reduce disulfide bonds to free thiols,
unfolding protein structure.
15. Hemoglobin is an example of which level of protein structure?
A) Primary
B) Secondary
C) Tertiary
D) Quaternary
Answer: D
Rationale: Hemoglobin consists of four polypeptide subunits (two α, two β) held together by
noncovalent interactions, making it a quaternary structure.
16. Which amino acid is the most flexible and often found in tight turns?
A) Proline
B) Glycine
C) Tryptophan
D) Isoleucine
Answer: B
Rationale: Glycine has the smallest side chain (single hydrogen), allowing maximum
conformational flexibility, and is frequently found in tight turns.
17. Which bond is formed during protein synthesis between the carboxyl group of one amino
acid and the amino group of the next?
A) Hydrogen bond
B) Ester bond
C) Peptide bond
D) Disulfide bond
Answer: C
Rationale: A peptide bond is a covalent amide bond formed between the α-carboxyl of one
amino acid and the α-amino of another during translation.
18. The α-helix is stabilized primarily by:
A) Hydrophobic interactions
B) Disulfide bonds
MOCK TEST 250 QUESTIONS WITH
CORRECT ANSWERS AND RATIONALES
PORTAGE CHEM 210 – REAL TEST PREP
SECTION 1: AMINO ACIDS & PROTEIN STRUCTURE (Questions 1–40)
1. Which amino acid has a side chain that contains a primary amino group and is often involved
in cross-linking proteins?
A) Cysteine
B) Lysine
C) Glutamate
D) Proline
Answer: B
Rationale: Lysine contains a primary amine (–NH₂) in its side chain. It is often involved in
cross-linking proteins and in post-translational modifications such as acetylation and ubiquitination.
2. Which amino acid is the only one with a side chain that can form disulfide bonds?
A) Methionine
B) Cysteine
C) Serine
D) Threonine
Answer: B
Rationale: Cysteine contains a thiol (–SH) group that can oxidize to form a disulfide bond (–S–S–)
with another cysteine, stabilizing protein tertiary and quaternary structure.
3. Which level of protein structure refers to the linear sequence of amino acids?
A) Primary
B) Secondary
C) Tertiary
D) Quaternary
Answer: A
Rationale: The primary structure of a protein is the linear sequence of amino acids held together
by covalent peptide bonds.
4. Which secondary structure is stabilized by hydrogen bonds between the carbonyl oxygen of
one residue and the amide hydrogen of a residue four residues away?
A) α-helix
B) β-sheet
,C) β-turn
D) Random coil
Answer: A
*Rationale: The α-helix is a right-handed coil stabilized by hydrogen bonds between the carbonyl
oxygen of residue n and the amide hydrogen of residue n+4.*
5. Which of the following amino acids is often found in β-turns because of its rigid cyclic structure?
A) Glycine
B) Alanine
C) Proline
D) Valine
Answer: C
Rationale: Proline has a rigid cyclic structure that forces a kink in the polypeptide chain, making it
common in β-turns and loops.
6. The peptide bond has partial double-bond character due to resonance. What is the
consequence of this?
A) The bond is freely rotatable
B) The bond is planar and rigid
C) The bond is weaker than a single bond
D) The bond is ionic
Answer: B
Rationale: Resonance delocalization of the lone pair on the amide nitrogen gives the peptide
bond about 40% double-bond character, making it planar and rigid.
7. Which amino acid is often called a "helix breaker" because it disrupts α-helix regularity?
A) Alanine
B) Leucine
C) Proline
D) Valine
Answer: C
Rationale: Proline lacks an amide hydrogen to participate in helix hydrogen bonding and its rigid
ring structure introduces a kink, disrupting α-helix regularity.
8. The isoelectric point (pI) of an amino acid is the pH at which:
A) The amino acid has no charge
B) The amino acid has maximum positive charge
C) The amino acid has maximum negative charge
D) The amino acid is fully protonated
Answer: A
Rationale: At the isoelectric point, the net charge of the amino acid or protein is zero. It will not
migrate in an electric field.
,9. Which of the following amino acids has a side chain that contains an aromatic ring?
A) Methionine
B) Phenylalanine
C) Serine
D) Asparagine
Answer: B
Rationale: Phenylalanine has a benzyl side chain (aromatic ring). Other aromatic amino acids are
tyrosine and tryptophan.
10. Which amino acid is the precursor for the neurotransmitter serotonin?
A) Tyrosine
B) Tryptophan
C) Histidine
D) Glutamate
Answer: B
Rationale: Tryptophan is hydroxylated to 5-hydroxytryptophan, which is decarboxylated to
serotonin (5-hydroxytryptamine).
11. Which type of interaction is primarily responsible for stabilizing the hydrophobic core of a
protein?
A) Hydrogen bonds
B) Ionic bonds
C) Hydrophobic interactions
D) Disulfide bonds
Answer: C
Rationale: Nonpolar amino acid side chains cluster together in the protein interior to minimize
contact with water, driven by hydrophobic interactions.
12. How many standard amino acids are found in proteins?
A) 18
B) 20
C) 22
D) 24
Answer: B
Rationale: There are 20 standard (proteinogenic) amino acids encoded by the universal genetic
code.
13. The technique that separates proteins based on their isoelectric point is called:
A) SDS-PAGE
B) Western blotting
C) Isoelectric focusing
D) Size-exclusion chromatography
, Answer: C
Rationale: Isoelectric focusing separates proteins based on their isoelectric point (pI) in a pH
gradient under an electric field.
14. Which reagent is commonly used to reduce disulfide bonds in proteins?
A) Urea
B) SDS
C) β-Mercaptoethanol
D) Coomassie blue
Answer: C
Rationale: β-Mercaptoethanol (and dithiothreitol, DTT) reduce disulfide bonds to free thiols,
unfolding protein structure.
15. Hemoglobin is an example of which level of protein structure?
A) Primary
B) Secondary
C) Tertiary
D) Quaternary
Answer: D
Rationale: Hemoglobin consists of four polypeptide subunits (two α, two β) held together by
noncovalent interactions, making it a quaternary structure.
16. Which amino acid is the most flexible and often found in tight turns?
A) Proline
B) Glycine
C) Tryptophan
D) Isoleucine
Answer: B
Rationale: Glycine has the smallest side chain (single hydrogen), allowing maximum
conformational flexibility, and is frequently found in tight turns.
17. Which bond is formed during protein synthesis between the carboxyl group of one amino
acid and the amino group of the next?
A) Hydrogen bond
B) Ester bond
C) Peptide bond
D) Disulfide bond
Answer: C
Rationale: A peptide bond is a covalent amide bond formed between the α-carboxyl of one
amino acid and the α-amino of another during translation.
18. The α-helix is stabilized primarily by:
A) Hydrophobic interactions
B) Disulfide bonds
