CHEM 153A Midterm 2 Exam | Questions
and Solutions
Fall 2026/2027 Update | 100% Correct –
UCLA
Biochemistry: Enzymes, Carbohydrates, and Introductory Metabolism | Key Domains:
Enzyme Kinetics, Enzyme Inhibition & Regulation, Carbohydrate Structure, Glycolysis,
Gluconeogenesis, Pyruvate Dehydrogenase, Bioenergetics
Introduction: This structured CHEM 153A Midterm 2 Exam for UCLA provides 60 high-quality,
exam-style questions with verified correct answers and detailed rationales for the Fall 2026/2027
term. Content emphasizes enzyme kinetics, carbohydrate chemistry, and core metabolic pathways
as covered in the second half of introductory biochemistry.
Exam Structure: Midterm 2 Exam (60 QUESTIONS)
Answer Format: Correct answers appear in bold cyan blue with rationales explaining kinetic
parameters, inhibition types, reaction mechanisms, or metabolic regulation.
CHEM 153A Midterm 2 Exam – 60 Verified Questions
1. In the Michaelis-Menten equation, Vmax represents:
A. The substrate concentration at half-maximal velocity
,B. The maximum velocity when enzyme is saturated with substrate
C. The dissociation constant of the ES complex
D. The turnover number of the enzyme
B. The maximum velocity when enzyme is saturated with substrate
Vmax is the theoretical maximum reaction rate achieved when all enzyme active sites are occupied
by substrate ([S] >> Km). It is dependent on total enzyme concentration (Vmax = kcat [E]total).
2. A Lineweaver-Burk plot for a competitive inhibitor shows:
A. Same y-intercept, different x-intercept
B. Same x-intercept, different y-intercept
C. Different slopes, same intercepts
D. Parallel lines
,A. Same y-intercept, different x-intercept
In competitive inhibition, Vmax is unchanged (same y-intercept = 1/Vmax), but Km increases
(x-intercept = –1/Km becomes less negative). Slopes increase with inhibitor concentration.
3. Which enzyme catalyzes the committed step of glycolysis?
A. Hexokinase
B. Phosphoglucose isomerase
C. Phosphofructokinase-1 (PFK-1)
D. Aldolase
C. Phosphofructokinase-1 (PFK-1)
PFK-1 catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate—the
first irreversible step unique to glycolysis (not shared with other pathways), making it the
committed step.
, 4. An uncompetitive inhibitor binds to:
A. The free enzyme only
B. The enzyme-substrate complex only
C. Both free enzyme and ES complex equally
D. The allosteric site regardless of substrate
B. The enzyme-substrate complex only
Uncompetitive inhibitors bind exclusively to the enzyme-substrate (ES) complex, not the free
enzyme. This decreases both apparent Km and Vmax proportionally.
5. Which molecule is a potent allosteric activator of PFK-1?
A. ATP
B. Citrate
and Solutions
Fall 2026/2027 Update | 100% Correct –
UCLA
Biochemistry: Enzymes, Carbohydrates, and Introductory Metabolism | Key Domains:
Enzyme Kinetics, Enzyme Inhibition & Regulation, Carbohydrate Structure, Glycolysis,
Gluconeogenesis, Pyruvate Dehydrogenase, Bioenergetics
Introduction: This structured CHEM 153A Midterm 2 Exam for UCLA provides 60 high-quality,
exam-style questions with verified correct answers and detailed rationales for the Fall 2026/2027
term. Content emphasizes enzyme kinetics, carbohydrate chemistry, and core metabolic pathways
as covered in the second half of introductory biochemistry.
Exam Structure: Midterm 2 Exam (60 QUESTIONS)
Answer Format: Correct answers appear in bold cyan blue with rationales explaining kinetic
parameters, inhibition types, reaction mechanisms, or metabolic regulation.
CHEM 153A Midterm 2 Exam – 60 Verified Questions
1. In the Michaelis-Menten equation, Vmax represents:
A. The substrate concentration at half-maximal velocity
,B. The maximum velocity when enzyme is saturated with substrate
C. The dissociation constant of the ES complex
D. The turnover number of the enzyme
B. The maximum velocity when enzyme is saturated with substrate
Vmax is the theoretical maximum reaction rate achieved when all enzyme active sites are occupied
by substrate ([S] >> Km). It is dependent on total enzyme concentration (Vmax = kcat [E]total).
2. A Lineweaver-Burk plot for a competitive inhibitor shows:
A. Same y-intercept, different x-intercept
B. Same x-intercept, different y-intercept
C. Different slopes, same intercepts
D. Parallel lines
,A. Same y-intercept, different x-intercept
In competitive inhibition, Vmax is unchanged (same y-intercept = 1/Vmax), but Km increases
(x-intercept = –1/Km becomes less negative). Slopes increase with inhibitor concentration.
3. Which enzyme catalyzes the committed step of glycolysis?
A. Hexokinase
B. Phosphoglucose isomerase
C. Phosphofructokinase-1 (PFK-1)
D. Aldolase
C. Phosphofructokinase-1 (PFK-1)
PFK-1 catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate—the
first irreversible step unique to glycolysis (not shared with other pathways), making it the
committed step.
, 4. An uncompetitive inhibitor binds to:
A. The free enzyme only
B. The enzyme-substrate complex only
C. Both free enzyme and ES complex equally
D. The allosteric site regardless of substrate
B. The enzyme-substrate complex only
Uncompetitive inhibitors bind exclusively to the enzyme-substrate (ES) complex, not the free
enzyme. This decreases both apparent Km and Vmax proportionally.
5. Which molecule is a potent allosteric activator of PFK-1?
A. ATP
B. Citrate
