CHEM 153A HOMEWORK 1 AND 2
ANSWER KEYS | 2026/27 UPDATED
| 100% CORRECT - UCLA.
50 Questions with Answers and Detailed Rationales
100 PERCENT GUARANTEED PASS
INSTANT DOWNLOAD ANSWERS INCLUDED
IMPORTANCE OF THIS DOCUMENT
This comprehensive examination preparation guide has been meticulously developed to help you succeed in the
CHEM 153A HOMEWORK 1 AND 2 ANSWER KEYS | 2026/27 UPDATED | 100% CORRECT - UCLA.. It
contains 50 carefully selected questions that reflect the most current exam content and testing strategies. Each
question is accompanied by a correct answer and a detailed rationale that explains the underlying
pathophysiology, pharmacology, or clinical reasoning.
Self-Assessment – Test your knowledge and Exam Preparation – Familiarize yourself with the
identify areas requiring further question format and content
study areas
Concept Reinforcement – Deepen your Confidence Building – Develop test-taking
understanding through strategies and reduce
evidence-based exam anxiety
rationales
Time Management – Practice answering
questions under simulated
exam conditions
Review Summary 50 Questions
Foundations - Application - CHEM 153a Homework 1 AND 2 KEYS 2026/27 Updated 100 Correct - UCLA
CHEM 153a Homework 1 AND 2 KEYS 2026/27 Updated 100 Correct - UCLA University
All answers with rationales
,Table of Contents
Content Area Questions Key Topics
Amino Acids AND Protein 1-9 Protein, Folding, Substrate, Lower, Directly
Structure
Protein Function AND 10-18 Protein, Likely, Enzyme, Disulfide BOND, SIDE Chain
Hemoglobin
Enzyme Kinetics AND 19-27 Effect, Enzyme S, State, Oxygen Affinity, Hemoglobin
Inhibition
Enzyme Mechanisms AND 28-36 State, Protein, Intermediate, Native, Likely
Regulation
Carbohydrates AND 37-45 Protein, Kinetic, Inhibitor, Constant, Enzyme
Glycobiology
Lipids AND Biological 46-50 Pharmacokinetic Parameter, Likely, Altered, Kidney, Homozygous
Membranes Loss-of-function Mutation
TOTAL 50 All questions include answers and detailed rationales
,Section A - Amino Acids AND Protein Structure
Q1.
In a hydrophobic collapse model of protein folding, a mutant protein with a
surface-exposed tryptophan replaced by valine shows slower folding kinetics. Which
thermodynamic principle best explains this observation?
A. Valine's smaller side chain reduces the B. The mutation increases the
hydrophobic driving force for the rate-limiting configurational entropy of the unfolded state,
collapse step. raising the activation barrier.
C. Tryptophan's aromatic ring stabilizes local D. Valine's -branching restricts main-chain
backbone contacts via - interactions, and its torsional angles, destabilizing the transition
loss removes a specific folding nucleus. state ensemble.
Correct: A - Valine's smaller side chain reduces the hydrophobic driving force for the
rate-limiting collapse step.
Rationale:In hydrophobic collapse, the burial of nonpolar side chains drives the initial
compaction. Replacing a large hydrophobic tryptophan with a smaller valine reduces the
hydrophobic effect's magnitude, slowing the collapse. While other factors can influence
folding, the hydrophobic driving force is the primary determinant in this model.
Why the other answers are wrong:
B. The unfolded state entropy change is not the direct cause of slower collapse kinetics.
C. Specific - interactions are not the primary determinant in the general hydrophobic collapse
model.
D. -branching effects on backbone conformations are secondary to the loss of hydrophobic
surface area.
Reference: Fersht, A. (2017). Structure and Mechanism in Protein Science, Ch. 18.
Q2.
A novel enzyme has a kcat/Km of 10^8 M^-1 s^-1 for its substrate. When the substrate
concentration is much lower than Km, which kinetic parameter most directly sets the
reaction velocity?
A. kcat B. Km
C. kcat/Km D. Enzyme concentration
Correct: C - kcat/Km
Rationale:At [S] << Km, the Michaelis-Menten equation simplifies to v = (kcat/Km)[E]t[S].
Thus, the apparent second-order rate constant kcat/Km directly determines velocity. kcat
alone does not account for the low substrate occupancy.
Page 3
, Section A - Amino Acids AND Protein Structure
Why the other answers are wrong:
A. kcat only limits velocity when the enzyme is saturated with substrate.
B. Km alone does not set velocity; it appears only in the context of the ratio.
D. Enzyme concentration is a scaling factor but the catalytic efficiency is set by kcat/Km.
Reference: Segel, I.H. (1993). Enzyme Kinetics, Ch. 2.
Q3.
A protein binds two ligands with positive cooperativity. The Hill coefficient is 2.5. Which of
the following statements about the binding is correct?
A. The protein must have at least 3 binding B. The protein has exactly 2 binding sites.
sites.
C. Binding of the first ligand increases the D. The protein undergoes a conformational
affinity of the second ligand, but the Hill change upon binding that is independent of
coefficient overestimates the number of ligand occupancy.
sites.
Correct: A - The protein must have at least 3 binding sites.
Rationale:The Hill coefficient is an upper bound for the number of binding sites. A Hill
coefficient of 2.5 indicates that the protein must have at least 3 cooperative binding sites (n_H
n). It cannot have exactly 2 sites because the maximum Hill coefficient for 2 sites is 2.
Positive cooperativity means sequential binding affinity increases.
Why the other answers are wrong:
B. A Hill coefficient cannot exceed the number of sites; 2.5 > 2 is impossible.
C. The Hill coefficient does not necessarily overestimate; it can be less than or equal to the
actual number of sites.
D. The statement describes a concerted model but is not a necessary consequence of a Hill
coefficient of 2.5.
Reference: Segel, I.H. (1993). Enzyme Kinetics, Ch. 7.
Q4.
Which experimental approach would most directly distinguish between the concerted
(MWC) and sequential (KNF) models of allosteric regulation?
A. Measuring equilibrium binding isotherms B. Observing hybrid states in a tetrameric
at various ligand concentrations. protein using single-molecule FRET.
C. Determining the Hill coefficient at D. Comparing the crystal structures of the
different ligand concentrations. unliganded and fully liganded states.
Correct: B - Observing hybrid states in a tetrameric protein using single-molecule FRET.
Page 4
ANSWER KEYS | 2026/27 UPDATED
| 100% CORRECT - UCLA.
50 Questions with Answers and Detailed Rationales
100 PERCENT GUARANTEED PASS
INSTANT DOWNLOAD ANSWERS INCLUDED
IMPORTANCE OF THIS DOCUMENT
This comprehensive examination preparation guide has been meticulously developed to help you succeed in the
CHEM 153A HOMEWORK 1 AND 2 ANSWER KEYS | 2026/27 UPDATED | 100% CORRECT - UCLA.. It
contains 50 carefully selected questions that reflect the most current exam content and testing strategies. Each
question is accompanied by a correct answer and a detailed rationale that explains the underlying
pathophysiology, pharmacology, or clinical reasoning.
Self-Assessment – Test your knowledge and Exam Preparation – Familiarize yourself with the
identify areas requiring further question format and content
study areas
Concept Reinforcement – Deepen your Confidence Building – Develop test-taking
understanding through strategies and reduce
evidence-based exam anxiety
rationales
Time Management – Practice answering
questions under simulated
exam conditions
Review Summary 50 Questions
Foundations - Application - CHEM 153a Homework 1 AND 2 KEYS 2026/27 Updated 100 Correct - UCLA
CHEM 153a Homework 1 AND 2 KEYS 2026/27 Updated 100 Correct - UCLA University
All answers with rationales
,Table of Contents
Content Area Questions Key Topics
Amino Acids AND Protein 1-9 Protein, Folding, Substrate, Lower, Directly
Structure
Protein Function AND 10-18 Protein, Likely, Enzyme, Disulfide BOND, SIDE Chain
Hemoglobin
Enzyme Kinetics AND 19-27 Effect, Enzyme S, State, Oxygen Affinity, Hemoglobin
Inhibition
Enzyme Mechanisms AND 28-36 State, Protein, Intermediate, Native, Likely
Regulation
Carbohydrates AND 37-45 Protein, Kinetic, Inhibitor, Constant, Enzyme
Glycobiology
Lipids AND Biological 46-50 Pharmacokinetic Parameter, Likely, Altered, Kidney, Homozygous
Membranes Loss-of-function Mutation
TOTAL 50 All questions include answers and detailed rationales
,Section A - Amino Acids AND Protein Structure
Q1.
In a hydrophobic collapse model of protein folding, a mutant protein with a
surface-exposed tryptophan replaced by valine shows slower folding kinetics. Which
thermodynamic principle best explains this observation?
A. Valine's smaller side chain reduces the B. The mutation increases the
hydrophobic driving force for the rate-limiting configurational entropy of the unfolded state,
collapse step. raising the activation barrier.
C. Tryptophan's aromatic ring stabilizes local D. Valine's -branching restricts main-chain
backbone contacts via - interactions, and its torsional angles, destabilizing the transition
loss removes a specific folding nucleus. state ensemble.
Correct: A - Valine's smaller side chain reduces the hydrophobic driving force for the
rate-limiting collapse step.
Rationale:In hydrophobic collapse, the burial of nonpolar side chains drives the initial
compaction. Replacing a large hydrophobic tryptophan with a smaller valine reduces the
hydrophobic effect's magnitude, slowing the collapse. While other factors can influence
folding, the hydrophobic driving force is the primary determinant in this model.
Why the other answers are wrong:
B. The unfolded state entropy change is not the direct cause of slower collapse kinetics.
C. Specific - interactions are not the primary determinant in the general hydrophobic collapse
model.
D. -branching effects on backbone conformations are secondary to the loss of hydrophobic
surface area.
Reference: Fersht, A. (2017). Structure and Mechanism in Protein Science, Ch. 18.
Q2.
A novel enzyme has a kcat/Km of 10^8 M^-1 s^-1 for its substrate. When the substrate
concentration is much lower than Km, which kinetic parameter most directly sets the
reaction velocity?
A. kcat B. Km
C. kcat/Km D. Enzyme concentration
Correct: C - kcat/Km
Rationale:At [S] << Km, the Michaelis-Menten equation simplifies to v = (kcat/Km)[E]t[S].
Thus, the apparent second-order rate constant kcat/Km directly determines velocity. kcat
alone does not account for the low substrate occupancy.
Page 3
, Section A - Amino Acids AND Protein Structure
Why the other answers are wrong:
A. kcat only limits velocity when the enzyme is saturated with substrate.
B. Km alone does not set velocity; it appears only in the context of the ratio.
D. Enzyme concentration is a scaling factor but the catalytic efficiency is set by kcat/Km.
Reference: Segel, I.H. (1993). Enzyme Kinetics, Ch. 2.
Q3.
A protein binds two ligands with positive cooperativity. The Hill coefficient is 2.5. Which of
the following statements about the binding is correct?
A. The protein must have at least 3 binding B. The protein has exactly 2 binding sites.
sites.
C. Binding of the first ligand increases the D. The protein undergoes a conformational
affinity of the second ligand, but the Hill change upon binding that is independent of
coefficient overestimates the number of ligand occupancy.
sites.
Correct: A - The protein must have at least 3 binding sites.
Rationale:The Hill coefficient is an upper bound for the number of binding sites. A Hill
coefficient of 2.5 indicates that the protein must have at least 3 cooperative binding sites (n_H
n). It cannot have exactly 2 sites because the maximum Hill coefficient for 2 sites is 2.
Positive cooperativity means sequential binding affinity increases.
Why the other answers are wrong:
B. A Hill coefficient cannot exceed the number of sites; 2.5 > 2 is impossible.
C. The Hill coefficient does not necessarily overestimate; it can be less than or equal to the
actual number of sites.
D. The statement describes a concerted model but is not a necessary consequence of a Hill
coefficient of 2.5.
Reference: Segel, I.H. (1993). Enzyme Kinetics, Ch. 7.
Q4.
Which experimental approach would most directly distinguish between the concerted
(MWC) and sequential (KNF) models of allosteric regulation?
A. Measuring equilibrium binding isotherms B. Observing hybrid states in a tetrameric
at various ligand concentrations. protein using single-molecule FRET.
C. Determining the Hill coefficient at D. Comparing the crystal structures of the
different ligand concentrations. unliganded and fully liganded states.
Correct: B - Observing hybrid states in a tetrameric protein using single-molecule FRET.
Page 4
