Page 1 of 147
“UWORLD FAILED QUESTIONSQUESTIONS &
ANSWERS EXAM 2026 ”LATEST EXAM 2026 –
2027 SOLVED QUESTIONS & ANSWERS
VERIFIED 100% GRADED A+ (LATEST VERSION)
WELL REVISED 100% GUARANTEE PASS
Uworld failed questions
In order to transport long-chain fatty acids from the cytosol to the
mitochondria, three of the following molecules are required. Which one is NOT
necessary?
A.Coenzyme A
B.ATP
C.Carnitine
D.Oxaloacetate
D
Entry into the mitochondrial matrix is tightly regulated by transport proteins in the
inner mitochondrial membrane. Fatty acids must be activated with coenzyme A
followed by carnitine to enter the mitochondrial matrix. Activation requires ATP
hydrolysis.
Which of the following catabolic pathways directly produce both ATP (or GTP)
and NADH?
Fatty acid oxidation
Glycolysis
The Krebs cycle
The electron transport chain
A.I and II only
B.II and III only
C.I, II, and III only
D.II, III, and IV only
, Page 2 of 147
B
Some catabolic pathways synthesize ATP (or GTP) directly; others synthesize
reduced electron carriers such as NADH, which can then enter the electron transport
chain to produce ATP; and some pathways do both. Glycolysis (Number II) produces
2 ATP molecules and 2 NADH molecules per glucose molecule consumed. The
pyruvate molecules resulting from glycolysis are then converted to acetyl-CoA.
Acetyl-CoA can enter the Krebs cycle (Number III), which produces 1 ATP molecule
(or GTP, depending on the organism), 3 NADH molecules, and 1 FADH2 molecule
per acetyl-CoA molecule. Therefore, both glycolysis and the Krebs cycle produce
ATP (or GTP) and NADH.
(Number I) Fatty acid oxidation directly produces NADH and acetyl-CoA. These
molecules can then enter the electron transport chain and the Krebs cycle,
respectively—eventually producing ATP—but fatty acid oxidation does not produce
ATP on its own.
(Number IV) The electron transport chain produces ATP by consuming NADH (and
FADH2), not producing it.
what is teh function of the parathyroid hormone released by the parathyroid
gland?
It increases plasma calcium concentration
and indirectly increases bone resorption (breakdown) by osteoclasts, bone-resorbing
cells, and causes decreased bone mineralization.
What is the function of the active form of vitamin D (calcitriol) PTH released by
in the kidneys?
active vitamin D primarily functions to promote absorption of dietary calcium from the
small intestine.
Enzyme A catalyzes the conversion of substrate S to product P. When enzyme
A is phosphorylated, its kcat value changes from 10 s−1 to 5 s−1 and its Km
value changes from 100 μM to 20 μM. If equal concentrations of each enzyme
form are used then compared to the unphosphorylated enzyme A, the
phosphorylated form:
A.has a higher catalytic efficiency and yields a faster reaction rate when [S] <
20 μM.
B.has a higher turnover number and yields a faster reaction rate under
saturating conditions.
C.has a lower affinity for S and yields a slower reaction rate at all [S].
D.is allosterically inhibited and yields a lower reaction rate at all [S].
A
The question indicates that enzyme A undergoes a decrease in both kcat and Km
upon phosphorylation. However, Km decreases by a greater factor than kcat, so the
kcat/Km ratio increases. Therefore, the phosphorylated form of the enzyme has a
higher catalytic efficiency than the unphosphorylated form, and the phosphorylated
form yields a faster reaction rate at low concentrations (eg, below 20 μM).
what is the formula for catalytic efficiency?
, Page 3 of 147
Catalytic efficiency is calculated as the ratio of the turnover number kcat to the
Michaelis constant Km (ie, catalytic efficiency = kcat/Km).
A higher kcat and/or a lower Km contribute to a higher catalytic efficiency, and
therefore to a faster reaction rate at low substrate concentrations relative to less-
efficient enzymes.
A protein denatures as ionic interactions are disrupted by deprotonation of
positively charged side chains. This is most likely the result of:
A.a decrease in the ionic strength of the solution.
B.an increase in the ionic strength of the solution.
C.a decrease in the pH of the solution.
D.an increase in the pH of the solution.
D
The question states that ionic bonds in a protein were disrupted by deprotonation.
Because deprotonation tends to occur in environments with a low concentration of
protons (ie, high pH), this result indicates an increase in the pH of the solution.
Reactions that follow Michaelis-Menten kinetics produce what type of curve?
a hyperbolic curve that shows reaction rate V0 as a function of substrate
concentration [S].
what is the relationship between the Lineweaver-Burk plot and the Michaelis-
Menten ?
A Lineweaver-Burk plot is a double-reciprocal plot of the Michaelis-Menten equation
and shows a linear relationship between 1/V0 and 1/[S]. The Lineweaver-Burk plot
can be inverted to regenerate the hyperbolic curve.
in Enzymatic reactions how do you know if it is a zero-order or first-order
reactions?
Enzymatic reactions typically behave as zero-order or first-order reactions.
In zero-order reactions, the rate is only dependent on the rate constant kcat because
substrate concentrations exceed the KM value.
First-order reactions depend on substrate concentration and occur when KM is
greater than the substrate concentration.
During prolonged fasting, which of the following liver enzymes has
upregulated activity?
A.Glycogen synthase
B.Pyruvate carboxylase
C.Glucokinase
D.Phosphofructokinase
B
The first step in gluconeogenesis is carboxylation of pyruvate to form oxaloacetate.
This step bypasses the irreversible pyruvate kinase reaction and is catalyzed by the
enzyme pyruvate carboxylase. In the well-fed state, pyruvate carboxylase is
downregulated so that pyruvate can be used in other pathways, but during prolonged
fasting, pyruvate carboxylase activity is upregulated in the liver to increase the rate
of gluconeogenesis.
Which of the following situations would NOT cause vasoconstriction to occur?
A.Loss of blood
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B.Exposure to cold temperatures
C.Increased blood pressure
D.Secretion of renin
C
During vasoconstriction, the smooth muscle surrounding the vessel contracts. This
results in a decrease in vessel diameter, which consequently increases the
resistance on blood flowing through the vessel. This increased resistance leads to an
increase in blood pressure. For example, if blood pressure were to decrease,
homeostatic mechanisms would cause vasoconstriction to occur, reversing this
decrease and leading to an increase in blood pressure, restoring homeostasis.
what is the function of renin?
It maintains blood pressure, activates angiotensin (produced in the kidneys)
In response to a decrease in blood pressure or blood volume, renin is secreted by
the kidney to promote vasoconstriction and increase blood pressure.
what decreases blood pressure to homeostasis levels?
Vasodilation
Somatic neural reflexes promote involuntary responses of skeletal muscles to
specific stimuli. Given this, a somatic neural reflex requires:
A.an afferent neuron.
B.an autonomic neuron.
C.both an afferent and an autonomic neuron.
D.neither an afferent nor an autonomic neuron.
A
Neural reflexes (ie, the reflexes in which neurons play a part) can be either somatic
(involving a skeletal muscle) or autonomic (involving tissues other than skeletal
muscle).
Both somatic and autonomic reflexes include an afferent neuron carrying sensory
information toward the central nervous system (CNS) and an efferent neuron that
activates a response in a target tissue.
The question states that neural reflexes involve involuntary responses to stimuli and
asks about the requirements for a neural reflex that activates a skeletal muscle to
occur. The simplest (ie, monosynaptic) somatic reflexes only require an afferent
neuron delivering the sensory information to the spinal cord and an efferent motor
neuron activating the muscle response.
what is teh step which blood flows through the circulatory system?
Accordingly, blood flows through the circulatory system as follows:
- Deoxygenated blood from body tissues enters the right atrium via the (superior and
inferior) vena cavae.
- The right atrium contracts, forcing the deoxygenated blood through the tricuspid
valve and into the right ventricle.
- The right ventricle contracts to propel the blood through the pulmonary valve and
into the pulmonary arteries.
- The pulmonary arteries carry blood from the heart to the capillary beds of lung
“UWORLD FAILED QUESTIONSQUESTIONS &
ANSWERS EXAM 2026 ”LATEST EXAM 2026 –
2027 SOLVED QUESTIONS & ANSWERS
VERIFIED 100% GRADED A+ (LATEST VERSION)
WELL REVISED 100% GUARANTEE PASS
Uworld failed questions
In order to transport long-chain fatty acids from the cytosol to the
mitochondria, three of the following molecules are required. Which one is NOT
necessary?
A.Coenzyme A
B.ATP
C.Carnitine
D.Oxaloacetate
D
Entry into the mitochondrial matrix is tightly regulated by transport proteins in the
inner mitochondrial membrane. Fatty acids must be activated with coenzyme A
followed by carnitine to enter the mitochondrial matrix. Activation requires ATP
hydrolysis.
Which of the following catabolic pathways directly produce both ATP (or GTP)
and NADH?
Fatty acid oxidation
Glycolysis
The Krebs cycle
The electron transport chain
A.I and II only
B.II and III only
C.I, II, and III only
D.II, III, and IV only
, Page 2 of 147
B
Some catabolic pathways synthesize ATP (or GTP) directly; others synthesize
reduced electron carriers such as NADH, which can then enter the electron transport
chain to produce ATP; and some pathways do both. Glycolysis (Number II) produces
2 ATP molecules and 2 NADH molecules per glucose molecule consumed. The
pyruvate molecules resulting from glycolysis are then converted to acetyl-CoA.
Acetyl-CoA can enter the Krebs cycle (Number III), which produces 1 ATP molecule
(or GTP, depending on the organism), 3 NADH molecules, and 1 FADH2 molecule
per acetyl-CoA molecule. Therefore, both glycolysis and the Krebs cycle produce
ATP (or GTP) and NADH.
(Number I) Fatty acid oxidation directly produces NADH and acetyl-CoA. These
molecules can then enter the electron transport chain and the Krebs cycle,
respectively—eventually producing ATP—but fatty acid oxidation does not produce
ATP on its own.
(Number IV) The electron transport chain produces ATP by consuming NADH (and
FADH2), not producing it.
what is teh function of the parathyroid hormone released by the parathyroid
gland?
It increases plasma calcium concentration
and indirectly increases bone resorption (breakdown) by osteoclasts, bone-resorbing
cells, and causes decreased bone mineralization.
What is the function of the active form of vitamin D (calcitriol) PTH released by
in the kidneys?
active vitamin D primarily functions to promote absorption of dietary calcium from the
small intestine.
Enzyme A catalyzes the conversion of substrate S to product P. When enzyme
A is phosphorylated, its kcat value changes from 10 s−1 to 5 s−1 and its Km
value changes from 100 μM to 20 μM. If equal concentrations of each enzyme
form are used then compared to the unphosphorylated enzyme A, the
phosphorylated form:
A.has a higher catalytic efficiency and yields a faster reaction rate when [S] <
20 μM.
B.has a higher turnover number and yields a faster reaction rate under
saturating conditions.
C.has a lower affinity for S and yields a slower reaction rate at all [S].
D.is allosterically inhibited and yields a lower reaction rate at all [S].
A
The question indicates that enzyme A undergoes a decrease in both kcat and Km
upon phosphorylation. However, Km decreases by a greater factor than kcat, so the
kcat/Km ratio increases. Therefore, the phosphorylated form of the enzyme has a
higher catalytic efficiency than the unphosphorylated form, and the phosphorylated
form yields a faster reaction rate at low concentrations (eg, below 20 μM).
what is the formula for catalytic efficiency?
, Page 3 of 147
Catalytic efficiency is calculated as the ratio of the turnover number kcat to the
Michaelis constant Km (ie, catalytic efficiency = kcat/Km).
A higher kcat and/or a lower Km contribute to a higher catalytic efficiency, and
therefore to a faster reaction rate at low substrate concentrations relative to less-
efficient enzymes.
A protein denatures as ionic interactions are disrupted by deprotonation of
positively charged side chains. This is most likely the result of:
A.a decrease in the ionic strength of the solution.
B.an increase in the ionic strength of the solution.
C.a decrease in the pH of the solution.
D.an increase in the pH of the solution.
D
The question states that ionic bonds in a protein were disrupted by deprotonation.
Because deprotonation tends to occur in environments with a low concentration of
protons (ie, high pH), this result indicates an increase in the pH of the solution.
Reactions that follow Michaelis-Menten kinetics produce what type of curve?
a hyperbolic curve that shows reaction rate V0 as a function of substrate
concentration [S].
what is the relationship between the Lineweaver-Burk plot and the Michaelis-
Menten ?
A Lineweaver-Burk plot is a double-reciprocal plot of the Michaelis-Menten equation
and shows a linear relationship between 1/V0 and 1/[S]. The Lineweaver-Burk plot
can be inverted to regenerate the hyperbolic curve.
in Enzymatic reactions how do you know if it is a zero-order or first-order
reactions?
Enzymatic reactions typically behave as zero-order or first-order reactions.
In zero-order reactions, the rate is only dependent on the rate constant kcat because
substrate concentrations exceed the KM value.
First-order reactions depend on substrate concentration and occur when KM is
greater than the substrate concentration.
During prolonged fasting, which of the following liver enzymes has
upregulated activity?
A.Glycogen synthase
B.Pyruvate carboxylase
C.Glucokinase
D.Phosphofructokinase
B
The first step in gluconeogenesis is carboxylation of pyruvate to form oxaloacetate.
This step bypasses the irreversible pyruvate kinase reaction and is catalyzed by the
enzyme pyruvate carboxylase. In the well-fed state, pyruvate carboxylase is
downregulated so that pyruvate can be used in other pathways, but during prolonged
fasting, pyruvate carboxylase activity is upregulated in the liver to increase the rate
of gluconeogenesis.
Which of the following situations would NOT cause vasoconstriction to occur?
A.Loss of blood
, Page 4 of 147
B.Exposure to cold temperatures
C.Increased blood pressure
D.Secretion of renin
C
During vasoconstriction, the smooth muscle surrounding the vessel contracts. This
results in a decrease in vessel diameter, which consequently increases the
resistance on blood flowing through the vessel. This increased resistance leads to an
increase in blood pressure. For example, if blood pressure were to decrease,
homeostatic mechanisms would cause vasoconstriction to occur, reversing this
decrease and leading to an increase in blood pressure, restoring homeostasis.
what is the function of renin?
It maintains blood pressure, activates angiotensin (produced in the kidneys)
In response to a decrease in blood pressure or blood volume, renin is secreted by
the kidney to promote vasoconstriction and increase blood pressure.
what decreases blood pressure to homeostasis levels?
Vasodilation
Somatic neural reflexes promote involuntary responses of skeletal muscles to
specific stimuli. Given this, a somatic neural reflex requires:
A.an afferent neuron.
B.an autonomic neuron.
C.both an afferent and an autonomic neuron.
D.neither an afferent nor an autonomic neuron.
A
Neural reflexes (ie, the reflexes in which neurons play a part) can be either somatic
(involving a skeletal muscle) or autonomic (involving tissues other than skeletal
muscle).
Both somatic and autonomic reflexes include an afferent neuron carrying sensory
information toward the central nervous system (CNS) and an efferent neuron that
activates a response in a target tissue.
The question states that neural reflexes involve involuntary responses to stimuli and
asks about the requirements for a neural reflex that activates a skeletal muscle to
occur. The simplest (ie, monosynaptic) somatic reflexes only require an afferent
neuron delivering the sensory information to the spinal cord and an efferent motor
neuron activating the muscle response.
what is teh step which blood flows through the circulatory system?
Accordingly, blood flows through the circulatory system as follows:
- Deoxygenated blood from body tissues enters the right atrium via the (superior and
inferior) vena cavae.
- The right atrium contracts, forcing the deoxygenated blood through the tricuspid
valve and into the right ventricle.
- The right ventricle contracts to propel the blood through the pulmonary valve and
into the pulmonary arteries.
- The pulmonary arteries carry blood from the heart to the capillary beds of lung
