AAMC MCAT 2026 EXAMINATION SET QUESTIONS AND
ANSWERS GUARANTEE A+
✔✔random order substrate binding - ✔✔either substrate could bind first
✔✔ordered substrate binding - ✔✔one substrate must bind the enzyme before the
second substrate is able to bind
✔✔Ping-Pong Substrate Binding - ✔✔binding of the first substrate causes the enzyme
to change into an intermediate form that will bind the second substrate.
✔✔double displacement substrate binding - ✔✔aka ping pong, binding of the first
substrate causes the enzyme to change into an intermediate form that will bind the
second substrate.
✔✔Wrong, Based on the passage, what is the primary type of interaction that RT makes
with Compound 2?
A.
Covalent
B.
Hydrogen bonds
C.
Ionic
D.
Hydrophobic - ✔✔D.
Hydrophobic, strongest RT interactions with the inhibitors come from the side chains of
valine and phenylalanine. These side chains are hydrophobic, so they would make
hydrophobic interactions with the inhibitor.
✔✔What is the approximate concentration of reaction product in a solution that has an
absorbance of 0.7 at pH 6.0?
A.
0.50 μM
B.
500 μM
C.
5 mM
D.
500 mM - ✔✔B.
500 μM A = εbc given in the passage, the concentration c is the absorbance A divided
by the absorptivity ε in a 1 cm path length cell. 0.7 divided by approximately 1400 gives
500 μM.
,✔✔The UV-VIS spectrophotometer used by the researchers contained a detector that
had low sensitivity and was unable to measure high absorbance samples. Which
approach to the experiment makes the most sense with this limitation in mind?
A.
The experiments done at high pH should be diluted relative to those at low pH, or the
path length of the high pH experiments should be decreased.
B.
The experiments done at low pH should be diluted relative to those at high pH, or the
path length of the high pH experiments should be decreased.
C.
The experiments done at high pH should be diluted relative to those at low pH, or the
path length of the low pH experiments should be decreased.
D.
The experiments done at low pH should be diluted relative to those at high pH, or the
path length of the low pH experiments should be decreased. - ✔✔A.
The experiments done at high pH should be diluted relative to those at low pH, or the
path length of the high pH experiments should be decreased, To not have an
absorbance reading that is below the limits of the detector, the experiments done at pH
values that result in the highest absorptivity should be diluted. The alternative is to
decrease the path length of the experiments that have the highest absorptivity.
✔✔Given that Tris has a pKa of 8.07, for how many of the experiments would Tris have
been an acceptable buffer?
A.
None of the experiments
B.
Only 1 of the experiments
C.
Only 2 of the experiments
D.
All three of the experiments - ✔✔C.
Only 2 of the experiments, A buffer has a buffering capacity that is ±1 pH unit away from
the pKa, which means that only two of the experiments would have used Tris.
✔✔iffy Based on the information in the passage, which description of an enzyme-
substrate covalent intermediate is most likely correct?
The substrate is covalently attached to:
A.
Asp14 through the phosphorus atom of the phosphate group.
B.
Asp14 through the oxygen atom of the phosphate group.
C.
Asp16 through the phosphorus atom of the phosphate group.
D.
Asp16 through the oxygen atom of the phosphate group. - ✔✔A.
,Asp14 through the phosphorus atom of the phosphate group., covalent intermediate will
occur through the nucleophilic substitution by the side chain carboxyl of Asp14 at the
electrophilic phosphorus atom in the substrate, displacing a leaving group.
✔✔What is the [H3O+] in the solution used in the experiment done at the lowest pH?
A.
0.01 μM
B.
0.1 μM
C.
1.0 μM
D.
100 μM - ✔✔C.
1.0 μM, The lowest pH is 6. Because pH = -log([H3O+]), [H3O+] = 1.0 × 10-6 M or 1.0
μM.
✔✔wrong, Based on the data in Table 1, what are the effects of increasing pH on
catalytic efficiency and the maximum velocity of the reaction?
A.
Both the catalytic efficiency and the maximum velocity of the reaction increase.
B.
The catalytic efficiency increases with pH, but the maximum velocity of the reaction
decreases.
C.
The catalytic efficiency decreases with pH, but the maximum velocity of the reaction
increases.
D.
Both the catalytic efficiency and the maximum velocity of the reaction decrease. - ✔✔D.
Both the catalytic efficiency and the maximum velocity of the reaction decrease., As pH
increases, the kcat decreases because it is proportional to the Vmax. Also, the catalytic
efficiency (kcat/KM) decreases because Vmax/KM is decreasing.
✔✔An unknown amount of a radioactive isotope with a half-life of 2.0 h was observed
for 6.0 h. If the amount of the isotope remaining after 6.0 h was 24 g, what would the
original amount have been?
A.
3g
B.
4g
C.
144 g
D.
192 g - ✔✔D.
192 g , Given the half-life T = 2 h, the duration t = 6 h represents 3 half-lives because 2
h × 3 = 6 h. According to the radioactive decay law N(t) = N0(1/2)t/T, the amount of
, remaining isotope is (1/2)3 = 1/8 of the original amount. The original amount was then 8
× 24 g = 192 g.
✔✔If a thin thread is placed between a screen and a bright source of light, a pattern of
parallel dark and bright fringes appears on the screen. The phenomenon best
explaining the formation of this pattern is:
A.
refraction.
B.
polarization.
C.
diffraction.
D.
reflection. - ✔✔C.
diffraction., The thin thread disrupts the propagation of light by impeding light to pass
through it. Diffraction causes the initially plane-parallel wave-fronts of light to change
direction and partially enter the shadow region behind the thread due to its narrowness.
The overlapping of different wave-fronts on the screen causes the pattern of dark and
bright fringes on the screen according to the phase difference between the wave-fronts
that interfere there.
✔✔Refraction - ✔✔The bending of a wave as it passes at an angle from one medium to
another
✔✔Polarization - ✔✔transverse wave, the direction of the oscillation is perpendicular to
the direction of motion of the wave.
✔✔Diffraction - ✔✔Occurs when an object causes a wave to change direction and bend
around it
✔✔Reflection - ✔✔The bouncing back of a wave when it hits a surface through which it
cannot pass.
✔✔wrong, Which saturated fatty acid is the most soluble in water?
A.
CH3(CH2)10COOH
B.
CH3(CH2)12COOH
C.
CH3(CH2)14COOH
D.
CH3(CH2)16COOH - ✔✔A.
CH3(CH2)10COOH, fatty acid that is the most soluble in water will have the shortest
alkyl chain
ANSWERS GUARANTEE A+
✔✔random order substrate binding - ✔✔either substrate could bind first
✔✔ordered substrate binding - ✔✔one substrate must bind the enzyme before the
second substrate is able to bind
✔✔Ping-Pong Substrate Binding - ✔✔binding of the first substrate causes the enzyme
to change into an intermediate form that will bind the second substrate.
✔✔double displacement substrate binding - ✔✔aka ping pong, binding of the first
substrate causes the enzyme to change into an intermediate form that will bind the
second substrate.
✔✔Wrong, Based on the passage, what is the primary type of interaction that RT makes
with Compound 2?
A.
Covalent
B.
Hydrogen bonds
C.
Ionic
D.
Hydrophobic - ✔✔D.
Hydrophobic, strongest RT interactions with the inhibitors come from the side chains of
valine and phenylalanine. These side chains are hydrophobic, so they would make
hydrophobic interactions with the inhibitor.
✔✔What is the approximate concentration of reaction product in a solution that has an
absorbance of 0.7 at pH 6.0?
A.
0.50 μM
B.
500 μM
C.
5 mM
D.
500 mM - ✔✔B.
500 μM A = εbc given in the passage, the concentration c is the absorbance A divided
by the absorptivity ε in a 1 cm path length cell. 0.7 divided by approximately 1400 gives
500 μM.
,✔✔The UV-VIS spectrophotometer used by the researchers contained a detector that
had low sensitivity and was unable to measure high absorbance samples. Which
approach to the experiment makes the most sense with this limitation in mind?
A.
The experiments done at high pH should be diluted relative to those at low pH, or the
path length of the high pH experiments should be decreased.
B.
The experiments done at low pH should be diluted relative to those at high pH, or the
path length of the high pH experiments should be decreased.
C.
The experiments done at high pH should be diluted relative to those at low pH, or the
path length of the low pH experiments should be decreased.
D.
The experiments done at low pH should be diluted relative to those at high pH, or the
path length of the low pH experiments should be decreased. - ✔✔A.
The experiments done at high pH should be diluted relative to those at low pH, or the
path length of the high pH experiments should be decreased, To not have an
absorbance reading that is below the limits of the detector, the experiments done at pH
values that result in the highest absorptivity should be diluted. The alternative is to
decrease the path length of the experiments that have the highest absorptivity.
✔✔Given that Tris has a pKa of 8.07, for how many of the experiments would Tris have
been an acceptable buffer?
A.
None of the experiments
B.
Only 1 of the experiments
C.
Only 2 of the experiments
D.
All three of the experiments - ✔✔C.
Only 2 of the experiments, A buffer has a buffering capacity that is ±1 pH unit away from
the pKa, which means that only two of the experiments would have used Tris.
✔✔iffy Based on the information in the passage, which description of an enzyme-
substrate covalent intermediate is most likely correct?
The substrate is covalently attached to:
A.
Asp14 through the phosphorus atom of the phosphate group.
B.
Asp14 through the oxygen atom of the phosphate group.
C.
Asp16 through the phosphorus atom of the phosphate group.
D.
Asp16 through the oxygen atom of the phosphate group. - ✔✔A.
,Asp14 through the phosphorus atom of the phosphate group., covalent intermediate will
occur through the nucleophilic substitution by the side chain carboxyl of Asp14 at the
electrophilic phosphorus atom in the substrate, displacing a leaving group.
✔✔What is the [H3O+] in the solution used in the experiment done at the lowest pH?
A.
0.01 μM
B.
0.1 μM
C.
1.0 μM
D.
100 μM - ✔✔C.
1.0 μM, The lowest pH is 6. Because pH = -log([H3O+]), [H3O+] = 1.0 × 10-6 M or 1.0
μM.
✔✔wrong, Based on the data in Table 1, what are the effects of increasing pH on
catalytic efficiency and the maximum velocity of the reaction?
A.
Both the catalytic efficiency and the maximum velocity of the reaction increase.
B.
The catalytic efficiency increases with pH, but the maximum velocity of the reaction
decreases.
C.
The catalytic efficiency decreases with pH, but the maximum velocity of the reaction
increases.
D.
Both the catalytic efficiency and the maximum velocity of the reaction decrease. - ✔✔D.
Both the catalytic efficiency and the maximum velocity of the reaction decrease., As pH
increases, the kcat decreases because it is proportional to the Vmax. Also, the catalytic
efficiency (kcat/KM) decreases because Vmax/KM is decreasing.
✔✔An unknown amount of a radioactive isotope with a half-life of 2.0 h was observed
for 6.0 h. If the amount of the isotope remaining after 6.0 h was 24 g, what would the
original amount have been?
A.
3g
B.
4g
C.
144 g
D.
192 g - ✔✔D.
192 g , Given the half-life T = 2 h, the duration t = 6 h represents 3 half-lives because 2
h × 3 = 6 h. According to the radioactive decay law N(t) = N0(1/2)t/T, the amount of
, remaining isotope is (1/2)3 = 1/8 of the original amount. The original amount was then 8
× 24 g = 192 g.
✔✔If a thin thread is placed between a screen and a bright source of light, a pattern of
parallel dark and bright fringes appears on the screen. The phenomenon best
explaining the formation of this pattern is:
A.
refraction.
B.
polarization.
C.
diffraction.
D.
reflection. - ✔✔C.
diffraction., The thin thread disrupts the propagation of light by impeding light to pass
through it. Diffraction causes the initially plane-parallel wave-fronts of light to change
direction and partially enter the shadow region behind the thread due to its narrowness.
The overlapping of different wave-fronts on the screen causes the pattern of dark and
bright fringes on the screen according to the phase difference between the wave-fronts
that interfere there.
✔✔Refraction - ✔✔The bending of a wave as it passes at an angle from one medium to
another
✔✔Polarization - ✔✔transverse wave, the direction of the oscillation is perpendicular to
the direction of motion of the wave.
✔✔Diffraction - ✔✔Occurs when an object causes a wave to change direction and bend
around it
✔✔Reflection - ✔✔The bouncing back of a wave when it hits a surface through which it
cannot pass.
✔✔wrong, Which saturated fatty acid is the most soluble in water?
A.
CH3(CH2)10COOH
B.
CH3(CH2)12COOH
C.
CH3(CH2)14COOH
D.
CH3(CH2)16COOH - ✔✔A.
CH3(CH2)10COOH, fatty acid that is the most soluble in water will have the shortest
alkyl chain
