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MCAT The Princeton Review AAMC Practice
Exam 2 - Biological and Biochemical
Foundations of Living Systems
Passage 1 (Questions 1 - 4)
Ultraviolet radiation (UVR) causes skin cancer by producing
mutagenic cyclobutane pyrimidine dimers (CPDs) and (6-4)
photoproducts (PPs) in DNA. In mice and humans, the nucleotide
excision repair system (NER) recognizes, removes, and replaces
segments of DNA strands that contain CPDs and (6-4) PPs.
Figure 1 shows how mouse skin levels of XPA (a damage-
recognition and rate-limiting factor in NER) and clock regulatory
protein CRY1 fluctuate in accordance with the internal
physiological and metabolic time keeper, the circadian clock.
Figures 2 and 3 show the circadian rhythms of NER activity and
DNA replication in mouse skin, respectively.
- The information in the passage suggests that in mice CRY
most likely affects XPA by:
A. activating XPA protein activity.
B. activating translation of XPA-encoding transcripts.
C. repressing replication of the XPA-encoding gene.
D. repressing transcription of the XPA-encoding gene.
Answer:
D. repressing transcription of the XPA-encoding gene
Reasoning:
This is a Biology question that falls under the content category
“Transmission of genetic information from the gene to the
protein.” The answer to this question is D because Figure 1
shows that XPA levels decrease as CRY1 levels increase. It is a
Scientific Reasoning and Problem Solving question because the
question involves determining which cellular process would lead
to a reduction in XPA levels.
- Which cells harvested from adult mice were most likely used as
the highly proliferative benchmark in the experiment that
generated the data shown in Figure 3?
A. Adipocytes
B. Cardiac muscle cells
C. Gastrointestinal epithelial cells
D. Neurons
Answer:
C. Neurons
Reasoning :
This is a Biology question that falls under the content category
“Structure and integrative functions of the main organ system.”
The answer to this question is C because the epithelial cells that
line the gastrointestinal tract are typically highly proliferative. It is
a Reasoning about the Design and Execution of Research
question because you must apply your knowledge of the different
cell types to predict which cell type would best suit the
experiment.
- After a section of a DNA strand containing a UVR-induced
lesion is removed and resynthesized, the newly synthesized
strand is rejoined to the remainder of the DNA strand by what
type of bond?
A. Disulfide
B. Hydrogen
C. Peptide
D. Phosphodiester
Answer :
D. Phosphodiester
Reasoning:
analysis of the effect of AlP on cytochrome oxidase (Figure 1).
Researchers measured the levels of ATP, the rate of ATP
synthesis, and the rate of ATP hydrolysis in rat liver mitochondria.
It was found that AlP exposure resulted in a 65% decrease in ATP
levels and a 48% decrease in the rate of ATP synthesis. In
addition, the effect of AlP on the activity of three ETC complexes
was determined (Table 1). The activities of these complexes were
determined independently of each other.
- AlP exposed to an aqueous solution in which pH range will
result in the largest amount of phosphine production?
A. pH < 4
B. 4 < pH < 7
C. 7 < pH < 10
D. pH > 10
Answer:
A. pH < 4
Reasoning:
This is a General Chemistry question that falls under the content
category “Principles of bioenergetics and fuel molecule
metabolism.” The answer to this question is A because H+ is a
reactant, and the increase in the concentration of H+ at low pH
will favor product formation. It is a Scientific Reasoning and
Problem Solving question because it is necessary to take the
information from the chemical equation in the passage and
reason about how changing solution conditions will affect that
reaction.
- Based on the passage, which amino acid will most likely react
with phosphine?
A. Met
B. Cys
C. Ser
D. Thr
Answer:
B. Cys
Reasoning :
This is an Organic Chemistry question that falls under the content
category “Structure and function of proteins and their constituent
amino acids.” The answer to this question is B because the
passage states that phosphine reacts with sulfhydryl groups, and
the cysteine side chain contains a sulfhydryl group. It is a
Knowledge of Scientific Concepts and Principles question
because you must recall the structure of the cysteine side chain
and apply it to the reactivity described in the passage.
- When researchers determined the total cellular concentration of
ATP in AlP-exposed rat liver cells, they found the concentration to
be equal to the control value. Which conclusion about the
metabolic state of the cell is best supported by these data?
A. Glycolytic flux is increased after AlP treatment.
B. Glycolytic flux is decreased after AlP treatment.
C. Citric acid cycle flux is increased after AlP treatment.
D. Citric acid cycle flux is decreased after AlP treatment.
Answer:
A. Glycolytic flux is increased after AIP treatment
Reasoning:
This is a Biochemistry question that falls under the content
category “Principles of bioenergetics and fuel molecule
metabolism.” The answer to this question is A because ATP
production is the same in both control and AlP-exposed cells, and
the data in the passage show that mitochondrial ATP production
is decreased. This indicates that the flux through glycolysis is
increased, because this would be the major pathway for ATP
production once the electron transport chain is shut down. It is a
Scientific Reasoning and Problem Solving question because you
C. Lysosome
Reasoning:
This is a Biology question that falls under the content category
“Assemblies of molecules, cells, and groups of cells within single
cellular and multicellular organisms.” The answer to this question
is C because when a macrophage ingests foreign material, the
material initially becomes trapped in a phagosome. The
phagosome then fuses with a lysosome to form a
phagolysosome. Inside the phagolysosome, enzymes digest the
foreign object. Of the cell structures listed, the labeled
carbohydrate is most likely to be microscopically visualized within
a lysosome (phagolysosome). It is a Scientific Reasoning and
Problem Solving question because the question makes a
scientific prediction.
- Inhibition of phosphofructokinase-1 by ATP is an example of:
I. allosteric regulation.
II. feedback inhibition.
III. competitive inhibition.
A. I only
B. III only
C. I and II only
D. II and III only
Answer :
C. I and II only
Reasoning:
This is a Biochemistry question that falls under the content
category “Structure and function of proteins and their constituent
amino acids.” The
answer to this question is C because ATP, the
end product of glycolysis, downregulates through feedback
inhibition the activity of phosphofructokinase-1 by binding to a
regulatory site other than the active site of the enzyme (allosteric
regulation). In contrast, competitive inhibition involves competition
for binding to the active site. It is a Scientific Reasoning and
Problem Solving question because you need to reason about how
the product of glycolysis (ATP) inhibits a regulatory enzyme of
glycolysis (phosphofructokinase-1).
- The graph shows the average relative concentration of ions in
pond water and in the cytoplasm of green algae cells. Which
process moves chlorine ions into the cells of the green algae?
A. Osmosis
B. Diffusion
C. Active transport
D. Facilitated diffusion
Answer :
C. Active Transport
Reasoning:
This is a Biology question that falls under the content category
“Assemblies of molecules, cells, and groups of cells within single
cellular and multicellular organisms.” The
answer to this question
is C because in order to maintain a higher concentration of
chlorine ions inside the cell, the ions must be moved into the cell
against their concentration gradient, which requires energy. This
process is active transport. In the other processes, ions would
move along their concentration gradient, either with or without the
help of transport proteins. It is a Knowledge of Scientific Concepts
and Principles question because it addresses assumed
knowledge of membrane transport processes.
- Dendrotoxin from the mamba snake blocks voltage-gated
potassium channels in somatic motor neurons that regulate
skeletal muscle contraction. In what way would initial exposure to
dendrotoxin affect the ability of a somatic motor neuron to
propagate an electrical signal in response to a stimulus?
A. It would inhibit the initiation of an action potential.
domains. Additional proteins in this pathway include the enzyme
casein kinase-1 (CK1), glycogen synthase kinase-3 (GSK3), and
β-catenin, which activates expression of Wnt target genes. In the
absence of Frizzled activation, CK1 and GSK3 sequentially
phosphorylate β-catenin, which targets it for ubiquitination. When
Frizzled is activated, CK1 and GSK3 activity is inhibited, and Wnt
target genes are transcribed (Figure 1). In healthy adult cardiac
tissue, the Wnt signaling pathway is silent; however, it is
reactivated by cardiac tissue injury.
- Based on the passage, which statement describes Wnt
proteins?
A. They are composed of multiple subunits.
B. They have a positive charge.
C. They are synthesized in the smooth endoplasmic reticulum.
D. They fold into their tertiary structure in the cytoplasm.
Answer:
B. They have a positive charge
Reasoning:
This is a Biochemistry question that falls under the content
category “Structure and function of proteins and their constituent
amino acids.” The answer to this question is B because based on
the passage, Wnt proteins are a family of secretory proteins with
isoelectric points around 9, implying that they are positively
charged at physiological pH. A is incorrect because there is no
information in the passage to support this response. C is incorrect
because secretory proteins are synthesized in the rough
endoplasmic reticulum. D is incorrect because folding of secretory
proteins occurs in the rough endoplasmic reticulum. It is a
Scientific Reasoning and Problem Solving question because it
requires you to estimate the charge of Wnt proteins, based on the
value of their isoelectric points as described in the passage.
- Based on the passage, β-catenin most likely has:
A. multiple subunits.
B. very few disulfide bonds.
C. a nuclear localization sequence.
D. a high proportion of surface-exposed nonpolar residues.
Answer:
C. a nuclear localization sequence
Reasoning:
This is a Biology question that falls under the content category
“Transmission of genetic information from the gene to the
protein.” The answer to this question is C because according to
Figure 1, β-catenin activates transcription factors for Wnt target
genes. As transcription factors are found in the nucleus, β-catenin
must enter the nucleus. Proteins that are translocated into the
nucleus usually contain a nuclear localization sequence. It is a
Scientific Reasoning and Problem Solving question because it
requires you to bring together assumed knowledge and passage-
based observations to make a conclusion.
- In the absence of Frizzled activation, β-catenin is covalently
modified and:
A. bound by a proteasome to initiate degradation into short
peptides.
B. translocated into the Golgi body for secretion through
exocytosis.
C. engulfed by a lysosome where it is hydrolyzed by proteases.
D. stored in vesicles until the signaling pathway is activated.
Answer:
A. bound by a proteasome to initiate degredation into short
peptides
Reasoning:
This is a Biology question that falls under the content category
“Transmission of genetic information from the gene to the
Protein X , its cDNA was cloned and expressed. The purified
protein was analyzed by gel electrophoresis under native,
denaturing, and denaturing/reducing conditions as shown in
Figure 1.
The fluorescent molecule 1-anilinonaphthalene-8-sulfonic acid
(ANS), which exhibits increased fluorescence upon binding to
hydrophobic surface residues of proteins, was used to probe for
conformational changes in Protein X in the presence of the
detergent dodecyl phosphocholine (DPC) (Figure 2).
To investigate the mechanism of Protein X pathogenicity,
researchers filled phospholipid-bound liposomes (micelles) with a
fluorescent dye. Addition of Protein X to the liposomes caused a
gradual release of the fluorescent dye from the liposomes (Figure
- Subunits of Protein X are linked covalently by bonds between
the:
A. thiol groups of methionine residues.
B. thiol groups of cysteine residues.
C. hydroxyl groups of serine residues.
D. hydroxyl groups of threonine residues.
Answer:
B. thiol groups of cysteine residues
Reasoning :
This is a Biochemistry question that falls under the content
category “Structure and function of proteins and their constituent
amino acids.” The answer to this question is B because Figure 1
shows that reducing agents separate subunits of Protein X. This
indicates that subunits of Protein X are linked together by disulfide
bonds, which implicate the thiol groups of cysteine residues. It is a
Knowledge of Scientific Concepts and Principles question
because it requires knowledge of the involvement of the thiol
groups of cysteine residues in the formation of disulfide bonds in
proteins.
- Based on the results in Figure 2, what effect does DPC have
on the hydrophobic amino acids in Protein X?
A. DPC phosphorylates these amino acids.
B. DPC hydrolyzes these amino acids.
C. DPC exposes these amino acids.
D. DPC suppresses these amino acids.
Answer:
C. DPC exposes these amino acids
Reasoning:
This is a Biochemistry question that falls under the content
category “Structure and function of proteins and their constituent
amino acids.” The answer to this question is C because Figure 2
shows that in the presence of DPC, Protein X has increased
fluorescence, indicating that it has adopted a conformation that
exposes hydrophobic residues on its surface. It is a Scientific
Reasoning and Problem Solving question because it requires
you to evaluate the information presented in Figure 2 to explain
the scientific basis of an observation.
- Which interpretation(s) is(are) consistent with the
observations in the passage?
I. Surface amino acids of Protein X are mostly hydrophilic in
aqueous solution.
II. Surface amino acids of Protein X are mostly hydrophilic in
presence of DPC.
III. Surface amino acids of Protein X are mostly hydrophobic in
presence of DPC.
A. I only
B. II only
C. III only
D. I and III only
Answer:
D. I and III only
Researchers investigated the roles of energy metabolism and
histone acetylation level in regulating the lifespan of yeast.
Experiment 1
Cells with deletion of the hst3 gene (Δ hst3 ), which encodes a
histone deacetylase; deletion of the rtt gene (Δ rtt ), which encodes
an acetyltransferase; or the double deletions of both genes
(Δ hst3 , Δrtt ) were prepared, and the lifespan for each mutant was
compared with the lifespan of wild-type cells (Figure 1).
Experiment 2
Cells with single deletion of the tdh2 gene (Δ tdh2 ), which encodes
glyceraldehyde-3-phosphate dehydrogenase (GAPDH), or double
deletions of the hst3 and tdh2 genes (Δ hst3 , Δ tdh2 ) were
prepared. The lifespan for each mutant was compared with the
lifespan of the Δ hst3 mutant and wild-type cells (Figure 2).
- The enzyme encoded by the tdh2 gene catalyzes the
reversible conversion of:
A. 3-phosphoglycerate to 1,3-bisphosphoglycerate.
B. glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate.
C. fructose-1,6-bisphosphate to glyceraldehyde-3-phosphate.
D. 2-phosphoglycerate to 3-phosphoglycerate.
Answer:
B. glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate
Reasoning :
This is a Biochemistry question that falls under the content
category “Principles of bioenergetics and fuel molecule
metabolism.” The answer to this question is B because GAPDH,
the enzyme encoded by the tdh2 gene, is a glycolytic enzyme that
catalyzes the reversible conversion of glyceraldehyde-3-
phosphate to 1,3-bisphosphoglycerate. It is a Knowledge of
Scientific Concepts and Principles question because it requires
knowledge of glycolytic enzymes and their substrates and
products.
- Based on Figure 1, how do the deletions of the hst3 or
the rtt genes affect the lifespan of yeast?
A. The deletion of the hst3 gene compensates for the ∆ rtt -induced
decrease in lifespan.
B. The deletion of the hst3 gene has no effect on the ∆ rtt -induced
increase in lifespan.
C. The deletion of the rtt gene compensates for the ∆ hst3 -induced
decrease in lifespan.
D. The deletion of the rtt gene has no effect on the ∆ hst3 -induced
decrease in lifespan.
Answer:
D. The deletion of the rtt gene has no effect on the ∆hst-3 induced
decrease in lifespan
Reasoning:
This is a Biology question that falls under the content category
“Processes of cell division, differentiation, and specialization.” The
answer to this question is D because according to data shown in
Figure 1, compared to wild type cells, the ∆ hst3 cells exhibit a
decrease in lifespan. Furthermore, the deletion of rtt gene in
∆ hst3 cells has no effect on the cells lifespan. It is a Scientific
Reasoning and Problem Solving question because you need to
evaluate data shown in Figure 1 and reason about how deletion of
genes affects the phenotypes in yeast.
- What is the best experimental method to analyze the effect
of tdh2 gene deletion on the rate of histone acetylation?
Comparing histone acetylation in wild-type and Δ tdh2 cells by:
A. Western blot
B. Southern blot
C. Northern blot
D. RT-PCR
Answer:
A. Western blot
- Vasopressin regulates the insertion of aquaporins into the
apical membranes of the epithelial cells of which renal structure?
A. Collecting duct
B. Proximal tubule
C. Bowman's capsule
D. Ascending loop of Henle
Answer:
A. Collecting duct
Reasoning:
This is a Biology question that falls under the content category
“Structure and functions of the nervous and endocrine systems
and ways in which these systems coordinate the organ systems.”
The answer to this question is A because vasopressin regulates
the fusion of aquaporins with the apical membranes of the
collecting duct epithelial cells. It is a Knowledge of Scientific
Concepts and Principles question because it requires knowledge
of hormone function in the excretory system.
- What are the primary myelin-forming cells in the peripheral
nervous system?
A. Microglia
B. Astrocytes
C. Schwann cells
D. Oligodendrocytes
Answer :
C. Schwann cells
Reasoning:
This is a Biology question that falls under the content category
“Structure and functions of the nervous and endocrine systems
and ways in which these systems coordinate the organ systems.”
The answer to this question is C because Schwann cells are the
myelin-forming cells in the peripheral nervous system. It is a
Knowledge of Scientific Concepts and Principles question
because it assesses knowledge of the different types of glia within
the nervous system.
- Osmotic pressure Π is given by the relation:
Π = iMRT
where i is the van’t Hoff factor, M is the concentration of
solute, R is the gas constant, and T is the temperature. The
osmotic pressure of sea water is approximately 24 atm at 25°C.
What is the approximate concentration of salt in sea water
(approximated by NaCl with i = 2)? (Note: Use R = 0.
L•atm/mol•K.)
A. 0.25 M
B. 0.50 M
C. 0.75 M
D. 1.0 M
Answer:
B. 0.50 M
Reasoning:
This is a General Chemistry question that falls under the content
category “Assemblies of molecules, cells, and groups of cells
within single cellular and multicellular organisms.” The answer to
this question is B since algebraic manipulation of the relation
gives M = Π/iRT = 24 atm / (2 × 0.08 L•atm/mol•K × 300 K) = 24 /
(2 × 24) mol/L = 0.5 M. It is a Scientific Reasoning and Problem
Solving question since you must manipulate a scientific formula
algebraically to solve a problem.
- A prion is best described as an infectious:
A. prokaryote.
B. transposon.
C. protein.
D. virus.
Answer:
C. protein
Reasoning :
This is a Biology question that falls under the content category
“The structure, growth, physiology, and genetics of prokaryotes
and viruses.” The answer to this question is C because a prion is
