,CHEM 210 Module 3 Exam | Biochemistry |
Portage Learning | Q & A | 2026 Edition
1. Which of the following best describes the primary structure of a protein?
A) The overall three-dimensional shape of a a single folded polypeptide
B) The linear sequence of amino acids linked by peptide bonds
C) The regular repeating folding patterns such as alpha helices and beta sheets
D) The arrangement of multiple polypeptide subunits into a functional complex
Correct Answer: The linear sequence of amino acids linked by peptide bonds
Rationale: The primary structure of a protein refers to the specific linear sequence of amino acids from
the N-terminus to the C-terminus, held together by covalent peptide bonds. Secondary structure
involves regular folding patterns, tertiary structure is the overall 3D shape of a single polypeptide, and
quaternary structure involves multiple subunits.
2. What is the primary function of myoglobin in muscle tissue?
A) Transport of oxygen from the lungs to tissues throughout the body
B) Storage and facilitated diffusion of oxygen within muscle cells
C) Catalysis of the conversion of carbon dioxide to bicarbonate
D) Regulation of blood pH through hydrogen ion binding
Correct Answer: Storage and facilitated diffusion of oxygen within muscle cells
Rationale: Myoglobin is a globular protein found in muscle tissue that stores oxygen and facilitates its
diffusion to mitochondria for aerobic respiration. Hemoglobin transports oxygen in the blood, while
carbonic anhydrase catalyzes CO₂ conversion. Myoglobin has a higher affinity for oxygen than
hemoglobin, allowing it to extract oxygen from blood.
3. According to the Michaelis-Menten model, what does Km represent?
A) The maximum velocity of an enzyme-catalyzed reaction
,B) The substrate concentration at which reaction velocity is half of Vmax
C) The turnover number of an enzyme molecule per second
D) The equilibrium constant for the enzyme-substrate complex formation
Correct Answer: The substrate concentration at which reaction velocity is half of Vmax
Rationale: Km (Michaelis constant) is the substrate concentration at which the reaction velocity equals
half of Vmax. It reflects the affinity of an enzyme for its substrate—a lower Km indicates higher affinity.
Vmax represents the maximum velocity, and kcat is the turnover number.
4. Which term refers to the regular coiled conformation of a polypeptide chain stabilized by hydrogen
bonds between backbone atoms?
A) Beta-pleated sheet
B) Alpha helix
C) Beta-turn
D) Random coil
Correct Answer: Alpha helix
Rationale: An alpha helix is a right-handed coiled conformation where hydrogen bonds form between
the carbonyl oxygen of one amino acid and the amide hydrogen of an amino acid four residues away.
Beta sheets involve hydrogen bonds between adjacent strands, and beta-turns reverse the direction of
the polypeptide chain.
5. A researcher is studying an enzyme that requires Zn²⁺ for catalytic activity. When the enzyme contains
Zn²⁺, it is called a(n):
A) Apoenzyme
B) Holoenzyme
C) Coenzyme
D) Prosthetic group
, Correct Answer: Holoenzyme
Rationale: A holoenzyme is the complete, catalytically active enzyme consisting of the apoenzyme
(protein portion) plus its required cofactor (such as a metal ion like Zn²⁺). An apoenzyme lacks the
cofactor and is inactive. Coenzymes are organic cofactors, and prosthetic groups are tightly bound
cofactors.
6. What is the most likely outcome if a competitive inhibitor is added to an enzyme-catalyzed reaction at
a fixed substrate concentration?
A) Vmax decreases and Km remains unchanged
B) Vmax remains unchanged and Km appears to increase
C) Both Vmax and Km decrease proportionally
D) Vmax increases and Km decreases
Correct Answer: Vmax remains unchanged and Km appears to increase
Rationale: Competitive inhibitors bind to the active site, competing with substrate. At sufficiently high
substrate concentrations, the inhibitor can be overcome, so Vmax remains unchanged. However, more
substrate is needed to reach half Vmax, so Km appears to increase (the enzyme's apparent affinity for
substrate decreases).
7. In the context of protein structure, what is a motif?
A) A complete folded polypeptide chain with independent function
B) A combination of secondary structure elements that form a recognizable pattern
C) The arrangement of multiple protein subunits in a complex
D) The specific amino acid sequence that determines protein folding
Correct Answer: A combination of secondary structure elements that form a recognizable pattern
Rationale: A motif (also called a supersecondary structure) is a combination of secondary structure
elements such as alpha helices and beta sheets arranged in a specific geometric pattern. Motifs are
smaller than domains and occupy a position between secondary and tertiary structure.
Portage Learning | Q & A | 2026 Edition
1. Which of the following best describes the primary structure of a protein?
A) The overall three-dimensional shape of a a single folded polypeptide
B) The linear sequence of amino acids linked by peptide bonds
C) The regular repeating folding patterns such as alpha helices and beta sheets
D) The arrangement of multiple polypeptide subunits into a functional complex
Correct Answer: The linear sequence of amino acids linked by peptide bonds
Rationale: The primary structure of a protein refers to the specific linear sequence of amino acids from
the N-terminus to the C-terminus, held together by covalent peptide bonds. Secondary structure
involves regular folding patterns, tertiary structure is the overall 3D shape of a single polypeptide, and
quaternary structure involves multiple subunits.
2. What is the primary function of myoglobin in muscle tissue?
A) Transport of oxygen from the lungs to tissues throughout the body
B) Storage and facilitated diffusion of oxygen within muscle cells
C) Catalysis of the conversion of carbon dioxide to bicarbonate
D) Regulation of blood pH through hydrogen ion binding
Correct Answer: Storage and facilitated diffusion of oxygen within muscle cells
Rationale: Myoglobin is a globular protein found in muscle tissue that stores oxygen and facilitates its
diffusion to mitochondria for aerobic respiration. Hemoglobin transports oxygen in the blood, while
carbonic anhydrase catalyzes CO₂ conversion. Myoglobin has a higher affinity for oxygen than
hemoglobin, allowing it to extract oxygen from blood.
3. According to the Michaelis-Menten model, what does Km represent?
A) The maximum velocity of an enzyme-catalyzed reaction
,B) The substrate concentration at which reaction velocity is half of Vmax
C) The turnover number of an enzyme molecule per second
D) The equilibrium constant for the enzyme-substrate complex formation
Correct Answer: The substrate concentration at which reaction velocity is half of Vmax
Rationale: Km (Michaelis constant) is the substrate concentration at which the reaction velocity equals
half of Vmax. It reflects the affinity of an enzyme for its substrate—a lower Km indicates higher affinity.
Vmax represents the maximum velocity, and kcat is the turnover number.
4. Which term refers to the regular coiled conformation of a polypeptide chain stabilized by hydrogen
bonds between backbone atoms?
A) Beta-pleated sheet
B) Alpha helix
C) Beta-turn
D) Random coil
Correct Answer: Alpha helix
Rationale: An alpha helix is a right-handed coiled conformation where hydrogen bonds form between
the carbonyl oxygen of one amino acid and the amide hydrogen of an amino acid four residues away.
Beta sheets involve hydrogen bonds between adjacent strands, and beta-turns reverse the direction of
the polypeptide chain.
5. A researcher is studying an enzyme that requires Zn²⁺ for catalytic activity. When the enzyme contains
Zn²⁺, it is called a(n):
A) Apoenzyme
B) Holoenzyme
C) Coenzyme
D) Prosthetic group
, Correct Answer: Holoenzyme
Rationale: A holoenzyme is the complete, catalytically active enzyme consisting of the apoenzyme
(protein portion) plus its required cofactor (such as a metal ion like Zn²⁺). An apoenzyme lacks the
cofactor and is inactive. Coenzymes are organic cofactors, and prosthetic groups are tightly bound
cofactors.
6. What is the most likely outcome if a competitive inhibitor is added to an enzyme-catalyzed reaction at
a fixed substrate concentration?
A) Vmax decreases and Km remains unchanged
B) Vmax remains unchanged and Km appears to increase
C) Both Vmax and Km decrease proportionally
D) Vmax increases and Km decreases
Correct Answer: Vmax remains unchanged and Km appears to increase
Rationale: Competitive inhibitors bind to the active site, competing with substrate. At sufficiently high
substrate concentrations, the inhibitor can be overcome, so Vmax remains unchanged. However, more
substrate is needed to reach half Vmax, so Km appears to increase (the enzyme's apparent affinity for
substrate decreases).
7. In the context of protein structure, what is a motif?
A) A complete folded polypeptide chain with independent function
B) A combination of secondary structure elements that form a recognizable pattern
C) The arrangement of multiple protein subunits in a complex
D) The specific amino acid sequence that determines protein folding
Correct Answer: A combination of secondary structure elements that form a recognizable pattern
Rationale: A motif (also called a supersecondary structure) is a combination of secondary structure
elements such as alpha helices and beta sheets arranged in a specific geometric pattern. Motifs are
smaller than domains and occupy a position between secondary and tertiary structure.
