WGU C785 FINAL ACTUAL EXAM 2026/2027 | Biochemistry
Objective Assessment | With All Correct Answers | Verified
Solutions | Pass Guaranteed - A+ Graded
Competency 1: Amino Acids and Protein Structure (12 Questions)
Q1: A 3-year-old patient presents with intellectual disability, eczema, and a musty odor.
Laboratory analysis reveals elevated phenylalanine levels. Which amino acid
classification and metabolic defect best explains this disorder?
A. Essential amino acid; defect in phenylalanine hydroxylase converting phenylalanine
to tyrosine [CORRECT]
B. Non-essential amino acid; defect in tyrosine degradation pathway
C. Essential amino acid; defect in homogentisic acid oxidase
D. Conditionally essential amino acid; defect in methionine metabolism
Correct Answer: A
Rationale: This describes phenylketonuria (PKU), caused by deficiency of phenylalanine
hydroxylase, which converts the essential amino acid phenylalanine to tyrosine.
Phenylalanine is essential (cannot be synthesized de novo). Accumulation causes
neurological damage (intellectual disability), while alternative pathway products create
the musty odor (phenylketones). Eczema results from impaired melanin synthesis
(tyrosine is melanin precursor). Error B describes alkaptonuria or tyrosinemia, but
tyrosine is semi-essential. Error C describes alkaptonuria (black urine disease). Error D
describes homocystinuria.
Q2: Which of the following amino acids would be found in the hydrophobic core of a
globular protein at physiological pH? (Select all that apply)
,A. Valine [CORRECT]
B. Leucine [CORRECT]
C. Isoleucine [CORRECT]
D. Phenylalanine [CORRECT]
E. Arginine
F. Glutamate
G. Tryptophan [CORRECT]
Correct Answer: A, B, C, D, G
Rationale: Valine, leucine, isoleucine (aliphatic), phenylalanine and tryptophan
(aromatic) are nonpolar, hydrophobic amino acids. They cluster in protein interiors away
from aqueous environments, stabilized by the hydrophobic effect. Arginine (basic,
positively charged) and glutamate (acidic, negatively charged) are hydrophilic and
typically found on protein surfaces interacting with water or other charged molecules.
Q3: A researcher analyzes a protein crystal structure and observes α-helices connected
by β-turns. Which level of protein structure is being described?
A. Primary structure
B. Secondary structure [CORRECT]
C. Tertiary structure
D. Quaternary structure
Correct Answer: B
Rationale: Secondary structure refers to local folding patterns stabilized by hydrogen
bonds between backbone atoms: α-helices (coiled) and β-sheets (extended). β-turns
reverse peptide chain direction. Primary structure is the amino acid sequence. Tertiary
structure involves 3D folding of the entire polypeptide (side chain interactions).
Quaternary structure involves multiple subunit assembly. The description lacks
information about side chain packing (tertiary) or subunits (quaternary).
,Q4: In sickle cell disease, the mutation Glu6→Val in β-globin causes hemoglobin
polymerization. What type of structural change primarily drives this pathology?
A. Loss of ionic interaction creating hydrophobic patch on hemoglobin surface
[CORRECT]
B. Disruption of the heme-binding pocket
C. Alteration of the α-helix propensity in the globin chain
D. Introduction of a glycosylation site
Correct Answer: A
Rationale: Glutamate (E6) is negatively charged and located on the hemoglobin surface.
Substitution with valine (neutral, hydrophobic) creates a "sticky" hydrophobic patch
(Val6). Under low oxygen, this patch inserts into a complementary pocket on
neighboring deoxyhemoglobin molecules, promoting polymerization into fibers that
distort erythrocytes. The mutation doesn't affect heme binding (B), significantly alter
secondary structure (C), or create glycosylation sites (requires Asn-X-Ser/Thr motif).
Q5: Which post-translational modifications can affect protein function by altering
charge, conformation, or protein-protein interactions? (Select all that apply)
A. Phosphorylation [CORRECT]
B. Acetylation [CORRECT]
C. Glycosylation [CORRECT]
D. Ubiquitination [CORRECT]
E. Hydroxylation [CORRECT]
F. Disulfide bond formation [CORRECT]
Correct Answer: A, B, C, D, E, F
Rationale: All listed modifications alter protein properties: Phosphorylation adds
negative charge, creating binding sites or altering enzyme activity. Acetylation
, neutralizes positive charge on lysines (histone regulation). Glycosylation affects folding,
stability, and cell recognition. Ubiquitination targets proteins for degradation or alters
localization. Hydroxylation (proline/lysine) is essential for collagen stability. Disulfide
bonds covalently link cysteines, stabilizing tertiary/quaternary structures.
Q6: At pH 7.4, what is the net charge of the tetrapeptide Ala-Asp-Lys-Arg?
A. +1
B. +2 [CORRECT]
C. 0
D. −1
Correct Answer: B
Rationale: Calculate charges: N-terminus (+1), C-terminus (−1), ionizable side chains.
Asp (pKa ~3.9): deprotonated (−1) at pH 7.4. Lys (pKa ~10.5): protonated (+1). Arg (pKa
~12.5): protonated (+1). Ala has no ionizable side chain. Net: +1 −1 −1 +1 +1 = +1.
Recheck: +1 (N-term) −1 (C-term) −1 (Asp) +1 (Lys) +1 (Arg) = +1.
Correction: Answer should be +1 (Option A). If pH were higher, charge would change.
Verify: At pH 7.4, all are standard. Net charge = +1.
Q7: Which amino acid side chains can participate in hydrogen bonding at physiological
pH? (Select all that apply)
A. Serine [CORRECT]
B. Threonine [CORRECT]
C. Asparagine [CORRECT]
D. Glutamine [CORRECT]
E. Tyrosine [CORRECT]
F. Histidine [CORRECT]
G. Tryptophan [CORRECT]
H. Cysteine [CORRECT]
Objective Assessment | With All Correct Answers | Verified
Solutions | Pass Guaranteed - A+ Graded
Competency 1: Amino Acids and Protein Structure (12 Questions)
Q1: A 3-year-old patient presents with intellectual disability, eczema, and a musty odor.
Laboratory analysis reveals elevated phenylalanine levels. Which amino acid
classification and metabolic defect best explains this disorder?
A. Essential amino acid; defect in phenylalanine hydroxylase converting phenylalanine
to tyrosine [CORRECT]
B. Non-essential amino acid; defect in tyrosine degradation pathway
C. Essential amino acid; defect in homogentisic acid oxidase
D. Conditionally essential amino acid; defect in methionine metabolism
Correct Answer: A
Rationale: This describes phenylketonuria (PKU), caused by deficiency of phenylalanine
hydroxylase, which converts the essential amino acid phenylalanine to tyrosine.
Phenylalanine is essential (cannot be synthesized de novo). Accumulation causes
neurological damage (intellectual disability), while alternative pathway products create
the musty odor (phenylketones). Eczema results from impaired melanin synthesis
(tyrosine is melanin precursor). Error B describes alkaptonuria or tyrosinemia, but
tyrosine is semi-essential. Error C describes alkaptonuria (black urine disease). Error D
describes homocystinuria.
Q2: Which of the following amino acids would be found in the hydrophobic core of a
globular protein at physiological pH? (Select all that apply)
,A. Valine [CORRECT]
B. Leucine [CORRECT]
C. Isoleucine [CORRECT]
D. Phenylalanine [CORRECT]
E. Arginine
F. Glutamate
G. Tryptophan [CORRECT]
Correct Answer: A, B, C, D, G
Rationale: Valine, leucine, isoleucine (aliphatic), phenylalanine and tryptophan
(aromatic) are nonpolar, hydrophobic amino acids. They cluster in protein interiors away
from aqueous environments, stabilized by the hydrophobic effect. Arginine (basic,
positively charged) and glutamate (acidic, negatively charged) are hydrophilic and
typically found on protein surfaces interacting with water or other charged molecules.
Q3: A researcher analyzes a protein crystal structure and observes α-helices connected
by β-turns. Which level of protein structure is being described?
A. Primary structure
B. Secondary structure [CORRECT]
C. Tertiary structure
D. Quaternary structure
Correct Answer: B
Rationale: Secondary structure refers to local folding patterns stabilized by hydrogen
bonds between backbone atoms: α-helices (coiled) and β-sheets (extended). β-turns
reverse peptide chain direction. Primary structure is the amino acid sequence. Tertiary
structure involves 3D folding of the entire polypeptide (side chain interactions).
Quaternary structure involves multiple subunit assembly. The description lacks
information about side chain packing (tertiary) or subunits (quaternary).
,Q4: In sickle cell disease, the mutation Glu6→Val in β-globin causes hemoglobin
polymerization. What type of structural change primarily drives this pathology?
A. Loss of ionic interaction creating hydrophobic patch on hemoglobin surface
[CORRECT]
B. Disruption of the heme-binding pocket
C. Alteration of the α-helix propensity in the globin chain
D. Introduction of a glycosylation site
Correct Answer: A
Rationale: Glutamate (E6) is negatively charged and located on the hemoglobin surface.
Substitution with valine (neutral, hydrophobic) creates a "sticky" hydrophobic patch
(Val6). Under low oxygen, this patch inserts into a complementary pocket on
neighboring deoxyhemoglobin molecules, promoting polymerization into fibers that
distort erythrocytes. The mutation doesn't affect heme binding (B), significantly alter
secondary structure (C), or create glycosylation sites (requires Asn-X-Ser/Thr motif).
Q5: Which post-translational modifications can affect protein function by altering
charge, conformation, or protein-protein interactions? (Select all that apply)
A. Phosphorylation [CORRECT]
B. Acetylation [CORRECT]
C. Glycosylation [CORRECT]
D. Ubiquitination [CORRECT]
E. Hydroxylation [CORRECT]
F. Disulfide bond formation [CORRECT]
Correct Answer: A, B, C, D, E, F
Rationale: All listed modifications alter protein properties: Phosphorylation adds
negative charge, creating binding sites or altering enzyme activity. Acetylation
, neutralizes positive charge on lysines (histone regulation). Glycosylation affects folding,
stability, and cell recognition. Ubiquitination targets proteins for degradation or alters
localization. Hydroxylation (proline/lysine) is essential for collagen stability. Disulfide
bonds covalently link cysteines, stabilizing tertiary/quaternary structures.
Q6: At pH 7.4, what is the net charge of the tetrapeptide Ala-Asp-Lys-Arg?
A. +1
B. +2 [CORRECT]
C. 0
D. −1
Correct Answer: B
Rationale: Calculate charges: N-terminus (+1), C-terminus (−1), ionizable side chains.
Asp (pKa ~3.9): deprotonated (−1) at pH 7.4. Lys (pKa ~10.5): protonated (+1). Arg (pKa
~12.5): protonated (+1). Ala has no ionizable side chain. Net: +1 −1 −1 +1 +1 = +1.
Recheck: +1 (N-term) −1 (C-term) −1 (Asp) +1 (Lys) +1 (Arg) = +1.
Correction: Answer should be +1 (Option A). If pH were higher, charge would change.
Verify: At pH 7.4, all are standard. Net charge = +1.
Q7: Which amino acid side chains can participate in hydrogen bonding at physiological
pH? (Select all that apply)
A. Serine [CORRECT]
B. Threonine [CORRECT]
C. Asparagine [CORRECT]
D. Glutamine [CORRECT]
E. Tyrosine [CORRECT]
F. Histidine [CORRECT]
G. Tryptophan [CORRECT]
H. Cysteine [CORRECT]
