Biochemistry C785 Midterm Practice Exam 2026 |WGU
1. Which level of protein structure is characterized by the sequence of amino
acids linked by peptide bonds?
A. Primary structure
B. Secondary structure
C. Tertiary structure
D. Quaternary structure
Answer: A
Rationale: The primary structure is the linear sequence of amino acids in a polypeptide
chain, held together by covalent peptide bonds.
2. Which molecule carries the genetic information from DNA to the ribosome for
protein synthesis?
A. tRNA
B. rRNA
C. mRNA
D. snRNA
Answer: C
Rationale: Messenger RNA (mRNA) acts as the intermediary that carries the genetic code
from the DNA in the nucleus to the ribosome.
,3. In DNA replication, which enzyme is responsible for unwinding the double
helix?
A. DNA Ligase
B. DNA Helicase
C. DNA Polymerase III
D. Topoisomerase
Answer: B
Rationale: DNA Helicase breaks the hydrogen bonds between the two strands of the DNA
double helix to ‘unzip’ them for replication.
4. What is the effect of a competitive inhibitor on an enzyme-catalyzed
reaction?
A. It increases Vmax and decreases Km
B. It keeps Vmax the same and increases Km
C. It decreases Vmax and keeps Km the same
D. It decreases both Vmax and Km
Answer: B
Rationale: Competitive inhibitors compete with the substrate for the active site, which
increases the apparent Km but does not change the maximum velocity (Vmax) because
enough substrate can outcompete the inhibitor.
5. Which of the following describes the ‘Bohr Effect’ in hemoglobin?
A. Low pH and high CO2 decrease oxygen affinity
B. High pH increases oxygen affinity
C. 2,3-BPG increases oxygen affinity
D. Low temperature causes oxygen release
Answer: A
Rationale: The Bohr Effect describes how acidic conditions (low pH) and high CO2
concentrations promote the release of oxygen from hemoglobin by stabilizing the T-state.
, 6. Which metabolic pathway occurs in the cytosol and breaks down glucose into
two molecules of pyruvate?
A. Glycolysis
B. Gluconeogenesis
C. Citric Acid Cycle
D. Oxidative Phosphorylation
Answer: A
Rationale: Glycolysis is the anaerobic process that occurs in the cytosol where one glucose
molecule is converted into two pyruvate molecules.
7. What type of bond stabilizes the secondary structure of proteins, such as
alpha-helices and beta-sheets?
A. Disulfide bonds
B. Hydrogen bonds
C. Ionic bonds
D. Peptide bonds
Answer: B
Rationale: Secondary structure is primarily stabilized by hydrogen bonds between the
backbone amino and carbonyl groups.
8. Which DNA repair mechanism specifically fixes pyrimidine dimers caused by
UV light?
A. Mismatch Repair
B. Base Excision Repair
C. Nucleotide Excision Repair
D. Homologous Recombination
Answer: C
Rationale: Nucleotide Excision Repair (NER) is the pathway responsible for removing
bulky lesions, such as thymine dimers induced by UV radiation.
1. Which level of protein structure is characterized by the sequence of amino
acids linked by peptide bonds?
A. Primary structure
B. Secondary structure
C. Tertiary structure
D. Quaternary structure
Answer: A
Rationale: The primary structure is the linear sequence of amino acids in a polypeptide
chain, held together by covalent peptide bonds.
2. Which molecule carries the genetic information from DNA to the ribosome for
protein synthesis?
A. tRNA
B. rRNA
C. mRNA
D. snRNA
Answer: C
Rationale: Messenger RNA (mRNA) acts as the intermediary that carries the genetic code
from the DNA in the nucleus to the ribosome.
,3. In DNA replication, which enzyme is responsible for unwinding the double
helix?
A. DNA Ligase
B. DNA Helicase
C. DNA Polymerase III
D. Topoisomerase
Answer: B
Rationale: DNA Helicase breaks the hydrogen bonds between the two strands of the DNA
double helix to ‘unzip’ them for replication.
4. What is the effect of a competitive inhibitor on an enzyme-catalyzed
reaction?
A. It increases Vmax and decreases Km
B. It keeps Vmax the same and increases Km
C. It decreases Vmax and keeps Km the same
D. It decreases both Vmax and Km
Answer: B
Rationale: Competitive inhibitors compete with the substrate for the active site, which
increases the apparent Km but does not change the maximum velocity (Vmax) because
enough substrate can outcompete the inhibitor.
5. Which of the following describes the ‘Bohr Effect’ in hemoglobin?
A. Low pH and high CO2 decrease oxygen affinity
B. High pH increases oxygen affinity
C. 2,3-BPG increases oxygen affinity
D. Low temperature causes oxygen release
Answer: A
Rationale: The Bohr Effect describes how acidic conditions (low pH) and high CO2
concentrations promote the release of oxygen from hemoglobin by stabilizing the T-state.
, 6. Which metabolic pathway occurs in the cytosol and breaks down glucose into
two molecules of pyruvate?
A. Glycolysis
B. Gluconeogenesis
C. Citric Acid Cycle
D. Oxidative Phosphorylation
Answer: A
Rationale: Glycolysis is the anaerobic process that occurs in the cytosol where one glucose
molecule is converted into two pyruvate molecules.
7. What type of bond stabilizes the secondary structure of proteins, such as
alpha-helices and beta-sheets?
A. Disulfide bonds
B. Hydrogen bonds
C. Ionic bonds
D. Peptide bonds
Answer: B
Rationale: Secondary structure is primarily stabilized by hydrogen bonds between the
backbone amino and carbonyl groups.
8. Which DNA repair mechanism specifically fixes pyrimidine dimers caused by
UV light?
A. Mismatch Repair
B. Base Excision Repair
C. Nucleotide Excision Repair
D. Homologous Recombination
Answer: C
Rationale: Nucleotide Excision Repair (NER) is the pathway responsible for removing
bulky lesions, such as thymine dimers induced by UV radiation.
