UNE MEDICAL BIOCHEMISTRY UNIT 1 TEST EXAM
LATEST VERSION 2025 QUESTIONS AND CORRECT
DETAILED ANSWERS (VERIFIED ANSWERS PLUS
RATIONALES) |ALREADY GRADED A+
Question 1
Hemoglobin is a large protein that consists of 4 subunits. Each subunit is composed of several
alpha-helices. The interactions of these helical domains with each other to form the final 3D shape of
a single subunit is best described as:
A) Primary structure of the protein
B) Secondary structure of the protein
C) Tertiary structure of the protein
D) Quaternary structure of the protein
E) Prosthetic group interaction
Correct Answer: C) Tertiary structure of the protein
Rationale: The primary structure is the amino acid sequence. The secondary structure refers
to local folding into alpha-helices and beta-sheets. The tertiary structure is the overall three-
dimensional folding of a single polypeptide chain, including the interactions between its
various secondary structural elements. Since the question describes the folding within a
single subunit, it is describing the tertiary structure.
Question 2
ATP is used to carry energy within the cell. The molecule consists of an adenine base, a ribose
sugar, and three phosphate groups (alpha, beta, gamma) linked in a chain. The majority of the
usable chemical energy is stored within which of the following bonds?
A) The glycosidic bond connecting adenine to the ribose sugar
B) The ester bond connecting the alpha-phosphate to the ribose sugar
C) The C-H bonds within the ribose sugar
D) The phosphoanhydride bonds linking the phosphate groups
E) The bonds within the adenine ring structure
Correct Answer: D) The phosphoanhydride bonds linking the phosphate groups
Rationale: The high energy of ATP is stored in the two phosphoanhydride bonds that link the
three phosphate groups. These bonds are "high energy" because their hydrolysis
(particularly the terminal gamma-phosphate) releases a significant amount of free energy,
which the cell can harness to drive endergonic reactions.
Question 3
An α-helical arrangement of amino acids, stabilized by hydrogen bonds between backbone atoms, is
considered to be part of what level of protein structure?
A) Primary structure
B) Secondary structure
C) Tertiary structure
,D) Quaternary structure
E) Prosthetic structure
Correct Answer: B) Secondary structure
Rationale: Protein structure is organized into levels. The primary structure is the linear
sequence of amino acids. The secondary structure refers to the local, repeating folding
patterns of the polypeptide backbone, primarily the α-helix and the β-sheet. These are
stabilized by a regular pattern of hydrogen bonds.
Question 4
The malate-aspartate shuttle is a critical system for transporting reducing equivalents from cytosolic
NADH into the mitochondrial matrix. Which molecule is reduced in the cytosol and then transported
into the mitochondria to carry these reducing equivalents?
A) Aspartate
B) Malate
C) Glutamate
D) Oxaloacetate
E) α-Ketoglutarate
Correct Answer: B) Malate
Rationale: In the cytosol, oxaloacetate accepts the reducing equivalents (electrons and a
proton) from NADH, becoming reduced to malate in a reaction catalyzed by cytosolic malate
dehydrogenase. Malate is then transported across the inner mitochondrial membrane. Inside
the matrix, malate is re-oxidized to oxaloacetate, regenerating NADH which can then enter the
electron transport chain.
Question 5
Given that the ion product of water (Kw) is 10⁻¹⁴ = [H+][OH-], what is the hydroxide ion [OH⁻]
concentration in a 0.001 M solution of hydrochloric acid (HCl)?
A) 10⁻³ M
B) 10⁻⁷ M
C) 10⁻¹¹ M
D) 10⁻¹⁴ M
E) 10⁻¹ M
Correct Answer: C) 10⁻¹¹ M
Rationale: HCl is a strong acid that completely dissociates in water. Therefore, a 0.001 M (or
10⁻³ M) solution of HCl will have a proton concentration [H⁺] of 10⁻³ M. Using the ion product
of water equation, we can solve for [OH⁻]: [OH⁻] = Kw / [H⁺] = 10⁻¹⁴ / 10⁻³ = 10⁻¹¹ M.
Question 6
Which of the following would be consistent with a thermodynamically favorable, or exergonic,
reaction?
, A) ΔG⁰ would be positive
B) ΔH would be positive
C) The reaction requires a net input of energy
D) ΔG⁰ would be negative
E) The Keq would be less than 1.0
Correct Answer: D) ΔG⁰ would be negative
Rationale: The Gibbs free energy change (ΔG) represents the energy available to do work. A
negative ΔG indicates an exergonic reaction, which releases energy and can proceed
spontaneously. A positive ΔG indicates an endergonic reaction, which requires an input of
energy.
Question 7
Hemoglobin has the ability to display cooperative binding of oxygen, while myoglobin does not.
Which of the following differences between the two proteins accounts for this?
A) The presence of a heme group in hemoglobin but not myoglobin
B) Hemoglobin is found in muscle while myoglobin is in the blood
C) The presence of quaternary structure in hemoglobin
D) Hemoglobin has a higher affinity for oxygen than myoglobin
E) Hemoglobin is composed of α-helices while myoglobin is composed of β-sheets
Correct Answer: C) The presence of quaternary structure in hemoglobin
Rationale: Cooperative binding requires communication between multiple binding sites.
Hemoglobin is a tetramer with four subunits (quaternary structure), allowing the binding of
oxygen to one subunit to induce a conformational change that increases the oxygen affinity
of the other subunits. Myoglobin is a monomer (no quaternary structure) with only one
binding site, so it cannot exhibit cooperativity.
Question 8
Which of the following is true for an exergonic reaction that proceeds spontaneously?
A) ΔG would be negative
B) ΔS would be negative
C) The reaction absorbs heat from the surroundings
D) ΔG would be positive
E) The reactants are more stable than the products
Correct Answer: A) ΔG would be negative
Rationale: The change in Gibbs free energy (ΔG) determines the spontaneity of a reaction. A
negative ΔG signifies that the reaction releases free energy and will proceed spontaneously
in the forward direction. This means the products are at a lower energy state and are more
stable than the reactants.
LATEST VERSION 2025 QUESTIONS AND CORRECT
DETAILED ANSWERS (VERIFIED ANSWERS PLUS
RATIONALES) |ALREADY GRADED A+
Question 1
Hemoglobin is a large protein that consists of 4 subunits. Each subunit is composed of several
alpha-helices. The interactions of these helical domains with each other to form the final 3D shape of
a single subunit is best described as:
A) Primary structure of the protein
B) Secondary structure of the protein
C) Tertiary structure of the protein
D) Quaternary structure of the protein
E) Prosthetic group interaction
Correct Answer: C) Tertiary structure of the protein
Rationale: The primary structure is the amino acid sequence. The secondary structure refers
to local folding into alpha-helices and beta-sheets. The tertiary structure is the overall three-
dimensional folding of a single polypeptide chain, including the interactions between its
various secondary structural elements. Since the question describes the folding within a
single subunit, it is describing the tertiary structure.
Question 2
ATP is used to carry energy within the cell. The molecule consists of an adenine base, a ribose
sugar, and three phosphate groups (alpha, beta, gamma) linked in a chain. The majority of the
usable chemical energy is stored within which of the following bonds?
A) The glycosidic bond connecting adenine to the ribose sugar
B) The ester bond connecting the alpha-phosphate to the ribose sugar
C) The C-H bonds within the ribose sugar
D) The phosphoanhydride bonds linking the phosphate groups
E) The bonds within the adenine ring structure
Correct Answer: D) The phosphoanhydride bonds linking the phosphate groups
Rationale: The high energy of ATP is stored in the two phosphoanhydride bonds that link the
three phosphate groups. These bonds are "high energy" because their hydrolysis
(particularly the terminal gamma-phosphate) releases a significant amount of free energy,
which the cell can harness to drive endergonic reactions.
Question 3
An α-helical arrangement of amino acids, stabilized by hydrogen bonds between backbone atoms, is
considered to be part of what level of protein structure?
A) Primary structure
B) Secondary structure
C) Tertiary structure
,D) Quaternary structure
E) Prosthetic structure
Correct Answer: B) Secondary structure
Rationale: Protein structure is organized into levels. The primary structure is the linear
sequence of amino acids. The secondary structure refers to the local, repeating folding
patterns of the polypeptide backbone, primarily the α-helix and the β-sheet. These are
stabilized by a regular pattern of hydrogen bonds.
Question 4
The malate-aspartate shuttle is a critical system for transporting reducing equivalents from cytosolic
NADH into the mitochondrial matrix. Which molecule is reduced in the cytosol and then transported
into the mitochondria to carry these reducing equivalents?
A) Aspartate
B) Malate
C) Glutamate
D) Oxaloacetate
E) α-Ketoglutarate
Correct Answer: B) Malate
Rationale: In the cytosol, oxaloacetate accepts the reducing equivalents (electrons and a
proton) from NADH, becoming reduced to malate in a reaction catalyzed by cytosolic malate
dehydrogenase. Malate is then transported across the inner mitochondrial membrane. Inside
the matrix, malate is re-oxidized to oxaloacetate, regenerating NADH which can then enter the
electron transport chain.
Question 5
Given that the ion product of water (Kw) is 10⁻¹⁴ = [H+][OH-], what is the hydroxide ion [OH⁻]
concentration in a 0.001 M solution of hydrochloric acid (HCl)?
A) 10⁻³ M
B) 10⁻⁷ M
C) 10⁻¹¹ M
D) 10⁻¹⁴ M
E) 10⁻¹ M
Correct Answer: C) 10⁻¹¹ M
Rationale: HCl is a strong acid that completely dissociates in water. Therefore, a 0.001 M (or
10⁻³ M) solution of HCl will have a proton concentration [H⁺] of 10⁻³ M. Using the ion product
of water equation, we can solve for [OH⁻]: [OH⁻] = Kw / [H⁺] = 10⁻¹⁴ / 10⁻³ = 10⁻¹¹ M.
Question 6
Which of the following would be consistent with a thermodynamically favorable, or exergonic,
reaction?
, A) ΔG⁰ would be positive
B) ΔH would be positive
C) The reaction requires a net input of energy
D) ΔG⁰ would be negative
E) The Keq would be less than 1.0
Correct Answer: D) ΔG⁰ would be negative
Rationale: The Gibbs free energy change (ΔG) represents the energy available to do work. A
negative ΔG indicates an exergonic reaction, which releases energy and can proceed
spontaneously. A positive ΔG indicates an endergonic reaction, which requires an input of
energy.
Question 7
Hemoglobin has the ability to display cooperative binding of oxygen, while myoglobin does not.
Which of the following differences between the two proteins accounts for this?
A) The presence of a heme group in hemoglobin but not myoglobin
B) Hemoglobin is found in muscle while myoglobin is in the blood
C) The presence of quaternary structure in hemoglobin
D) Hemoglobin has a higher affinity for oxygen than myoglobin
E) Hemoglobin is composed of α-helices while myoglobin is composed of β-sheets
Correct Answer: C) The presence of quaternary structure in hemoglobin
Rationale: Cooperative binding requires communication between multiple binding sites.
Hemoglobin is a tetramer with four subunits (quaternary structure), allowing the binding of
oxygen to one subunit to induce a conformational change that increases the oxygen affinity
of the other subunits. Myoglobin is a monomer (no quaternary structure) with only one
binding site, so it cannot exhibit cooperativity.
Question 8
Which of the following is true for an exergonic reaction that proceeds spontaneously?
A) ΔG would be negative
B) ΔS would be negative
C) The reaction absorbs heat from the surroundings
D) ΔG would be positive
E) The reactants are more stable than the products
Correct Answer: A) ΔG would be negative
Rationale: The change in Gibbs free energy (ΔG) determines the spontaneity of a reaction. A
negative ΔG signifies that the reaction releases free energy and will proceed spontaneously
in the forward direction. This means the products are at a lower energy state and are more
stable than the reactants.
