Practice MCAT 1 - Questions I got wrong

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What is the value of Kb for the conjugate base of a weak organic acid that has a pKa of 5? A. 10−2.5 B. 10−5 C. 10−9 D. 10−10

Solution: The correct answer is C. Because pKb = 14 - pKa, this is the Kb for the conjugate base of an acid with a pKa of 5.

Which amino acid exhibits a beta-branched side chain? A. Alanine B. Leucine C. Isoleucine D. Glycine

Solution: The correct answer is C. Alanine does not contain a branched side chain. Leucine does not contain a branched side chain. Isoleucine contains a branched side chain. Glycine does not contain a branched side chain.

Do pancreatic alpha cells secrete insulin or glucagon? Do pancreatic beta cells secrete insulin or glucagon?

glucagon insulin

Is glucagon secreted when blood glucose is high or low? Is insulin secreted when blood glucose is high or low?

low high

what is a ligand?

any molecule or atom that irreversibly binds to a receiving protein molecule

Which nerve type give CNS integration for a pain reflex arc?

interneurons

Look at definition side for the question Solution: The correct answer is A. This modification will increase the rate of formation, not the final yield of ester.

An ester is prepared by the method of direct esterification using an esterase enzyme as a catalyst. Which of the following modifications will NOT appreciably increase the final yield of ester? A. Using 2 times as much enzyme B. Using 2 moles of RCOOH instead of 1 mole C. Using 2 moles of RCH2OH instead of 1 mole D. Removing RCOOCH2R from the reaction mixture as it is formed

Where is Ki on a semi-log plot of concentration-dependent inhibition?

At the inflection point, or the steepest portion of the graph

Look at the back for the question Solution: The correct answer is C. Normal kidney transplants have low levels of miR-155, while high levels of miR-155 are associated with acute rejection. Thus, an individual with high levels of miR-155 is likely to benefit from treatment with immunosuppressors. Acute rejection is associated with low levels of let-7c, thus individuals with low let-7c levels are likely to benefit from treatment with immunosuppressors. Based on Figure 1, high levels of miR-30a-3p are associated with normal transplant. These data suggest that such individuals would not benefit from the treatment with immunosuppressors. Low levels of miR-10b are present in individuals experiencing acute rejection. Thus, treatment with immunosuppressors would benefit them.

Based on Figure 1, which patient is LEAST likely to benefit from therapy with immunosuppressors? A patient whose transplanted kidneys are associated with miRNA expression patterns characterized by: A. high levels of miR-155 B. low levels of let-7c. C. high levels of miR-30a-3p. D. low levels of miR-10b.

Approximately how many moles of Kr+ are contained in the laser tube at 0°C and 1 atm? A. 3 x 10-7 B. 2 x 10-6 C. 4 x 10-5 D. 5 x 10-4

Solution: The correct answer is D. There is 1 mole of gas in a volume of 22.4 L = 2.24 x 10 cm3 at STP; there are approximately 5 x 10-4 moles in 11 cm3.

What is perceptual constancy?

perceiving objects as unchanging even as illumination and retinal images change

What is Weber's Law?

the principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount)

How do you read a semi-log plot?

Each dash represents

Look at definition side for the question Solution: The correct answer is D. On the 25 μF capacitor, the power supply stores a charge of 25 μF × 3000 V = 75 mC. On the 30 μF capacitor, the same charge is stored by a power supply that has a voltage of 75 mC/30 μF = 2500 V.

If the 25 μF capacitor in the defibrillator in Figure 1 is replaced with a 30 μF capacitor, what new power supply setting would produce the same amount of charge? A. 3600 V B. 3500 V C. 3000 V D. 2500 V

Many blues musicians in the United States, particularly artists who grew up in the South during the first half of the twentieth century, experienced economic and other challenges and are often depicted as struggling artists with limited resources. At first glance, the Delta Blues Museum in Clarksdale, MS, seems not to portray blues artists in this conventional way. For instance, one exhibit chronicling the history of the blues includes a picture of Robert Johnson holding an acoustic guitar and wearing a fashionable pinstripe suit with a handkerchief neatly tucked in the front pocket. One of only two surviving photographs of Johnson, the picture was taken in a professional studio. The museum even contains a life-size mannequin of Muddy Waters dressed in an immaculate white suit and holding an expensive Gibson electric guitar. Beyond these visual representations of the artists as well-dressed and successful musicians, brief narratives from blues experts acknowledge the musicians' important contributions to American popular culture. Upon closer examination, however, these symbols of success are overshadowed by the museum's concerted efforts to construct what many people perceive as more "authentic" images of blues musicians. This strategy takes various forms. First, examples of blues artists' material struggles abound in the collection. In a memorial to Big Joe Williams, the guitarist is pictured playing his guitar on his porch. Although Williams is the focal point of the picture, the deteriorating porch and exterior wall, along with what appears to be a dirt driveway, suggest the musician's limited means. There are also a number of tattered instruments on display. Many of the exhibit's acoustic guitars, for example, are disfigured, reflecting the difficult and uncompromising lives of their former owners. The wooden body of Big Joe Williams's guitar, for example, is filled with scratches and nicks, the frets are worn, and the finish on the guitar neck is missing in several places, revealing a black undercoat. Visitors will also find well-used harmonicas and percussion instruments protected in a glass display case. Although technically "silent," the instruments play a song of the artist's history, craft, struggle, and legacy. While one cannot deny that many of these musicians were forced to survive in a world of poverty and grueling, labor-intensive employment, it is also true that some blues musicians, including B.B. King, Buddy Guy, Robert Cray, and others, amassed considerable personal fortunes. The museum's exhibits are constructed to satisfy the expectations of tourists who seek out images of what they perceive as an authentic blues culture. This display strategy not only works to legitimize and reinforce the image of the authentic blues singer, it also embodies larger marketing and promotional strategies designed to perpetuate the romantic vision of the Mississippi Delta as the mythical birthplace of the blues. For many blues tourists, the Delta serves as the last bastion of an authentic blues culture apparently untainted by the more commercial aspects of marketing and tourism. Despite this perception, several Southern states are capitalizing on the popularity of the blues and the potential financial windfall generated from tourists. According to ethnomusicologist Jeff Todd Titon, recent efforts reflect the "new blues tourism," an organized attempt to create a mediated experience for tourists ironically seeking an "authentic" and "genuine" blues experience. The new blues tourism is an example of niche tourism that capitalizes on the efforts of communities to accentuate their cultural heritage in an effort to increase their revenue from tourism as an industry. Question Based on the passage, the "many blues tourists" referred to in paragraph 4 seek an experience most like: A. that of theater-goers who prefer to see plays performed in the language they were written in. B. that of film-goers who generally attend more popular films before they see more obscure films. C. that of sports fans who attend professional sporting events but rarely watch them on television. D. that of viewers who prefer to see artists' drawings that were never advertised for sale.

Solution: The correct answer is D. There is no implication that the tourists seek something specifically "original," or seek to find music that is closest to the way it was originally done or performed. There is no implication that tourists are seeking something particularly popular. There is no implication that the tourists prefer live to televised or filmed events. The "many tourists" mentioned in the passage seek a blues culture "apparently untainted by the more commercial aspects of marketing and tourism" (paragraph 4). This is the only option that mentions an interest in something that is not for sale.

What does mutable mean?

liable to change

They used the fluorescence spectrometer depicted in Figure 2, which employs a 86Kr+ laser Kr has an atomic number of 36 What is the number of neutrons in the nucleus of the atom used to produce laser radiations? A. 48 B. 49 C. 50 D. 51

C. 50

Look at definition side for the question Solution: The correct answer is A. The full charge of the capacitor is 25 μF × 3000 V = 75 mC. The average discharge current is (75 mC)/(10 ms) = 7.5 A.

If the defibrillator described in the passage were fully charged and the entire charge were discharged through a patient in 10 ms, which of the following is closest to the average electrical current that would flow through the paddles? A. 7.5 A B. 15 A C. 22.5 A D. 30 A

Look at definition side for the question Solution: The correct answer is B. The work generated by the person while pushing the cart is equal to the area under the force-distance line, according to the definition of work. The area is equal to 1/2 × (100 N - 0 N) × (20 m - 0 m) = (100 N × 20 m)/2 = 1000 J.

Question A person pushes on a rolling cart with a force that diminishes with time because the person must walk faster to keep up with the accelerating cart. How much work does the person generate while pushing on the cart? A. 500 J B. 1000 J C. 2000 J D. 4000 J

Which classification of amino acids applies to the Trp residues after photochemical modification by CCl3CO2H? A. Acidic B. Basic C. Hydrophobic D. Polar neutral

Solution: The correct answer is A. The Trp residues after being photochemically modified by CCl3CO2H have a carboxylic acid group attached to the benzene ring.

Buffer B is 50 mM NH4CH3CO2, pH 6.5 What is the name of the ionic compound used to make Buffer B? A. Ammonium formate B. Ammonium carbonate C. Ammonium bicarbonate D. Ammonium acetate

Solution: The correct answer is D. A. Ammonium formate is NH4HCO2. B. Ammonium carbonate is (NH4)2CO3. C. Ammonium bicarbonate is NH4HCO3, a component of Buffer A. D. Ammonium acetate is NH4CH3CO2, a component of Buffer B.

Compound 1: Ki = 60.3 μM What quantity of Compound 1 must be provided to prepare 100.00 mL of solution with a concentration equal to Ki? A. 48.4 mg B. 24.2 mg C. 5.64 mg D. 2.92 mg

Solution: The correct answer is D. In 100.00 mL solution, 60.3 μM Compound 1 contains 6.03 μmol, which when converted to mol and multiplied by the molar mass, yields 0.00292 g or 2.92 mg.

Changes in the healthcare system have resulted in the transfer of some care activities away from hospitals to settings such as the patient's home. The responsibility for the day-to-day care of a patient then usually rests with family members. This changes the social roles and responsibilities for both the patient and family caregiver(s), which can raise particular issues when the patient has advanced cancer. The increased participation of family caregiving for cancer patients has led researchers and therapists to study the health and well-being of caregivers. This area of research focuses on balancing the psychosocial needs of the caregiver, so that he or she can more effectively attend to the needs of the patient. For example, caregivers often help with pain management for a family member with advanced cancer. Healthcare providers tend to focus on pharmacological pain control, but patients and caregivers also rely on nonpharmacological approaches to pain management, such as distraction, emotional support, and hot or cold therapies. The problem of pain management is usually solved after caregivers try multiple approaches and combinations of strategies until they find one that works for the patient. The problems facing family caregivers of advanced cancer patients differ based on the family's demographic characteristics. Research has found that caregivers with lower levels of income and education report more problems with the caregiving role. Caregiver distress that results from attending to a family member with advanced cancer also varies by gender and by age. Some of the factors, responses, and strategies that researchers and therapists have considered in the context of family caregiving are listed below. Factors that affect caregiving roles Demographic characteristics (for example, age, gender, culture) Disease situation (for example, cancer site, stage, and treatment) Caregiver responses to care demands Mental health (for example, depression, anxiety, burnout, distress) Physical health (for example, fatigue, insomnia, poor diet, morbidity) Strategies to assist family caregivers Informational (for example, conferences, books, pamphlets, websites) Therapeutic (for example, support groups, counseling, classes) More research is still needed, such as studies that determine how support for caregivers could be improved and how providers can help caregivers manage their new roles. Question When caring for a family member with advanced cancer, caregivers are often faced with the demands of completing many tasks for the patient while maintaining employment and other personal responsibilities. This situation describes which role dynamic? A. Role conflict B. Role adjustment C. Role strain D. Role engulfment

Solution: The correct answer is A. A. This is the correct answer. Role conflict occurs when the separate roles that an individual occupies come into conflict. The conflicting demands of being a caregiver and being an employee best describes a role conflict. B. Role adjustment refers to the process of an individual taking up a new social role. The example does not describe role adjustment. C. Role strain refers to the stress an individual experiences due to the competing demands within the same social role. The prompt describes conflicting demands of different social roles; therefore, role strain does not apply to this example. D. Role engulfment would have occurred if the care role was a dominant sense of identity. Role engulfment is not relevant to the example described in the prompt.

Solution: The correct answer is A. According to the passage, UCP1 directly reduces the proton gradient driving oxidative phosphorylation. This proton gradient is used to drive ATP synthesis by ATP synthase. The passage notes that UCP1 interferes with the function of oxidative phosphorylation. Pyruvate kinase carries out substrate-level phosphorylation, not oxidative phosphorylation. Na+/K+-ATPase is involved in ion transport and is not directly involved in oxidative phosphorylation. The passage notes that UCP1 interferes with the function of oxidative phosphorylation. Succinyl-CoA synthetase is an enzyme that performs substrate-level phosphorylation, not oxidative phosphorylation.

Consider the fully protonated amino acid shown. As the pH of a solution of this amino acid is raised, which group deprotonates first? A. I (a carboxyl group with two Cl atoms at the alpha carbon B. II (a carboxyl group with an amine bound at the alpha carbon)

Solution: The correct answer is A. As the pH is raised, the most acidic group deprotonates first. Of the choices, two are carboxylic acids, one is a hydroxyl group, and one is a protonated amine. The hydroxyl group is least acidic, while the protonated amine is less acidic (pKa ~ 10) than a carboxylic acid group (pKa ~ 5). Of the two carboxylic acid groups, the one next to the chlorine atoms will be more acidic since its conjugate base (an anion) will be stabilized by an inductive effect which dissipates negative charge building up.

Of these miRNAs, miR-142-5p, miR-155, and miR-223 are highly expressed in normal lymphocytes and monocytes, whereas miR-30a-3p, miR-10b, and let-7c are highly expressed in normal human renal cells. Experiment 2 Using AR biopsy specimens, researchers measured the levels of CD3 (T cell) mRNA and CD20 (B cell) mRNA and determined that there was a positive correlation between these mRNA levels and the levels of miR-142-5p, miR-155, and miR-223 but not with miR-10b, miR-30a-3p and let-7c. The association observed experimentally between the expression of miRNAs and mRNAs in AR kidney transplants indicates that miRNAs regulate the expression of genes implicated in which type(s) of immune response(s)? A. Adaptive immunity only B. Humoral immunity only C. Innate and cell-mediated immunity only D. Adaptive and innate immunity only

Solution: The correct answer is A. Based on Experiment 2, only the expression of T and B cell mRNAs is positively correlated with the three miRNAs analyzed (miR-142-5p, miR-155, and miR-223). T and B cells belong to the adaptive immune system: T cells regulate cell-mediated responses and B cells regulate humoral responses.

In operant conditioning, partial reinforcement, rather than continuous reinforcement, leads to a response that is: A. slower to acquire and more resistant to extinction. B. faster to acquire and less resistant to extinction. C. faster to acquire and more resistant to extinction. D. slower to acquire and less resistant to extinction.

Solution: The correct answer is A. Continuous reinforcement refers to reinforcing every response emitted by an individual. Partial reinforcement occurs when only some of the responses emitted by an individual are reinforced. Continuous reinforcement is associated with a fast rate of acquisition, but quicker extinction. Partial reinforcement, on the other hand, is associated with slower acquisition and slower extinction. Compared to continuous reinforcement, partial reinforcement results in slower acquisition and greater resistance to extinction. Compared to continuous reinforcement, partial reinforcement results in slower acquisition. Compared to continuous reinforcement, partial reinforcement results in greater resistance to extinction.

Cow's milk allergy (CMA) and lactose intolerance both result from dietary exposure to cow's milk and are often confused. CMA is caused by an abnormal inflammatory response to one or more proteins in cow's milk. Although more than one mechanism appears to be involved in generating this response, the antibody-mediated response is the best understood. Development of the antibody-mediated response occurs in two stages, the first being the generation of an abnormal immune response during initial exposure to milk proteins and the second being the generation of an inflammatory response upon subsequent exposure. Symptoms of antibody-mediated CMA may include hives and respiratory difficulty. Anaphylactic shock rarely occurs but can be fatal if not treated immediately. Lactose intolerance, also known as lactase deficiency, is a condition that results from insufficient synthesis of the enzyme lactase, which converts lactose into glucose and galactose. Although all healthy newborns produce sufficient levels of lactase, two distinct phenotypes exist in adults: lactase persistence (LP) (includes heterozygotes) and lactase non-persistence (LNP). LP adults continue to produce lactase into adulthood, whereas LNP individuals do not. It has been suggested that the LP phenotype is the result of a mutation event that coincided with the domestication of dairy animals thousands of years ago in areas such as northwestern Europe and within some Afro-Arabian nomadic populations. In Northwestern Europeans, sets of alleles located closely together on the same chromosome (haplotypes) associated with the LP phenotype contain several single nucleotide polymorphisms (SNPs). However, only one appears to be directly responsible for this phenotype; the others are silent. By comparison, several different SNPs appear to be directly responsible for the LP phenotype in Afro-Arabian LP-associated haplotypes. Question Which cells express lactase? A. Enterocytes of the duodenal villi B. Epithelial cells of the colon lining C. Parietal cells of the stomach lining D. Bile-producing hepatocytes of the liver

Solution: The correct answer is A. Enterocytes are the intestinal cells that produce Enzymes that digest disaccharides. This includes lactase. Colonocytes do not produce digestive enzymes. Lactose digestion by the body does not occur in the colon, though bacteria in the colon may break unusual sugars (oligosaccharides) down. Parietal cells of the stomach produce HCl, they do not produce digestive enzymes. Hepatocytes do not produce digestive enzymes.

E = -13.6/n2 eV wavelength of a photon could then be found with the equation λ = hc/E, where E is the energy of the photon, h = 4.1 × 10-15 eV•s is Planck's constant, and c = 3 × 108 m/s is the speed of light. If the red line in the Balmer series has a wavelength of 656 nm, which of the following is closest to its frequency? A. 4.6 × 1014 Hz B. 4.6 × 10−14 Hz C. 2.1 × 1015 Hz D. 2.1 × 10−15 Hz

Solution: The correct answer is A. For light that travels in vacuum, wavelength and frequency are related according to wavelength × frequency = 3.0 × 108 m/s. Solving for frequency yields (3.0 × 108 m/s)/(656 × 10-9 m) = 4.6 × 1014 Hz.

Look on back Solution: The correct answer is C. Based on Table 1, a decrease in gram-positive bacteria (Ruminococcaceae and Clostridia) will be linked to a reduction, not an increase, in acetate production. According to Table 1 only Roseburia use acetate as a source of energy. Roseburia are gram-positive bacteria. Thus, a reduction of gram positive bacteria is most likely to be associated to a reduction, not an increase, in the use of acetate. As indicated by the table, Ruminococcaceae consume H+. Reduction in gram-positive Ruminococcaceae results into higher levels of H+ and, as a consequence, an acidic pH. None of the bacteria assessed, regardless of gram status, produce polysaccharides (PS). Consequently, reducing the number of gram-positive bacteria will not likely affect PS production.

Based on Table 1, what is most likely associated with a reduction in gram-positive bacteria? A. Increase in acetate production B. Increase in use of acetate C. Decrease in pH D. Decrease in PS production

Look on back Solution: The correct answer is D. The genomic radiograph indicates an SNP containing both cytosine and thymine. These nucleobases are pyrimidines, not purines. The radiograph shows an SNP containing cytosine and thymine at the same position. Both of these are pyrimidines. Based on the radiograph, cytosine and thymine are the two nucleobases that occupy the same position within the SNP. These nucleobases are pyrimidines. The radiograph indicates an SNP containing both a cytosine and thymine nucleotide, instead of just thymine. Since both nucleobases are pyrimidines, this indicates that the SNP resulted from the mutation of a pyrimidine to another pyrimidine.

Cow's milk allergy (CMA) and lactose intolerance both result from dietary exposure to cow's milk and are often confused. CMA is caused by an abnormal inflammatory response to one or more proteins in cow's milk. Although more than one mechanism appears to be involved in generating this response, the antibody-mediated response is the best understood. Development of the antibody-mediated response occurs in two stages, the first being the generation of an abnormal immune response during initial exposure to milk proteins and the second being the generation of an inflammatory response upon subsequent exposure. Symptoms of antibody-mediated CMA may include hives and respiratory difficulty. Anaphylactic shock rarely occurs but can be fatal if not treated immediately. Lactose intolerance, also known as lactase deficiency, is a condition that results from insufficient synthesis of the enzyme lactase, which converts lactose into glucose and galactose. Although all healthy newborns produce sufficient levels of lactase, two distinct phenotypes exist in adults: lactase persistence (LP) (includes heterozygotes) and lactase non-persistence (LNP). LP adults continue to produce lactase into adulthood, whereas LNP individuals do not. It has been suggested that the LP phenotype is the result of a mutation event that coincided with the domestication of dairy animals thousands of years ago in areas such as northwestern Europe and within some Afro-Arabian nomadic populations. In Northwestern Europeans, sets of alleles located closely together on the same chromosome (haplotypes) associated with the LP phenotype contain several single nucleotide polymorphisms (SNPs). However, only one appears to be directly responsible for this phenotype; the others are silent. By comparison, several different SNPs appear to be directly responsible for the LP phenotype in Afro-Arabian LP-associated haplotypes. Question One of the silent SNPs present in the Northwestern European haplotype that is associated with LP resides within the lactase gene. Genomic DNA and cDNA of the region containing this SNP in an LP heterozygous adult was sequenced. The sequence results are shown. The SNP resulted from what type of mutation? A. Purine to purine B. Purine to pyrimidine C. Pyrimidine to purine D. Pyrimidine to pyrimidine

Look at definition side for the question Solution: The correct answer is B. A. Because the capacitance is directly proportional to the area of the parallel plates, a decrease in the area corresponds to a decrease in the capacitance. Given that the charge on the capacitor is directly proportional to the capacitance, a decreased capacitance results in a decrease in the charge as long as the power supply voltage is constant. B. Capacitance C is inversely proportional to the separation d between the parallel plates according to the formula C =(ϵ0 ϵr A)/d. A decrease in the separation corresponds to an increase in the capacitance. Given that the charge on the capacitor is directly proportional to the capacitance, an increased capacitance results in an increase in the charge as long as the power supply voltage is constant. C. Capacitance C is directly proportional to the permittivity ϵr > 1 of the dielectric between the parallel plates according to the formula C =(ϵ0 ϵr A)/d. Removing the dielectric essentially means decreasing the permittivity ϵr to 1, which corresponds to a decrease in the capacitance. Given that the charge on the capacitor is directly proportional to the capacitance, a decreased capacitance results in a decrease in the charge as long as the power supply voltage is constant. D. The charge on the capacitor is directly proportional to the capacitance multiplied by the voltage of the power supply. Decreasing the voltage results in a decrease in the charge unless the capacitance is increased independently.

If both the capacitor and the power supply in Figure 1 are adjustable, which of the following changes would result in an increase in the charge on the capacitor? A. Decreasing the area of the parallel plates B. Decreasing the separation between the parallel plates C. Removing the dielectric from the capacitor D. Decreasing the voltage of the power supply

Look on back Solution: The correct answer is D. The passage indicates that 5-HT activation results in an increase in cAMP levels, a hallmark of G-protein activation, not protein kinases. The passage indicates that 5-HT activation results in an increase in cAMP levels, a hallmark of G-protein activation, not tyrosine kinase receptors. The passage indicates that 5-HT activation results in an increase in cAMP levels, a hallmark of G-protein activation, not ligand-gated ion channels. The passage notes that 5-HTR4 is a transmembrane protein that binds 5-HT. Figure 2 shows that cell stimulation with 5-HT increases cAMP levels when its cell receptor, 5-HTR4, is present. This suggests that 5-HTR4 is a G protein-coupled receptor because cAMP is known to be produced during G protein-coupled receptor-triggered

Selective serotonin reuptake inhibitors (SSRIs) are drugs that can alleviate symptoms of depression by blocking the reuptake of serotonin (5-HT) from the synaptic cleft, thereby increasing the amount of time that 5-HT remains active. Elevated levels of 5-HT within the synapse are associated with feelings of well-being; conversely, low levels of 5-HT are correlated with depressive symptoms. Recent studies have shown that SSRIs can also mediate their antidepressant effects by increasing brain levels of certain cytokines, including interferon gamma (IFNγ). IFNγ directly induces the expression of the protein p11 in neighboring neurons, which then interacts with 5-HTR4, a 5-HT transmembrane receptor. Figures 1 and 2 provide information about this interaction. Figure 1 5-HTR4 protein expression in plasma membrane-enriched fraction (MEM) of hippocampal lysate and in total hippocampal lysate (TOT) from p11 wild-type (WT) or p11 knockout (KO) mice Figure 2 Effect of 5-HT on cAMP levels in cells transfected with 5-HTR4 and/or p11 Studies have shown that analgesics, such as ibuprofen (IBU), inhibit the behavioral antidepressant responses normally observed in mice undergoing chronic SSRI administration. Figure 3 shows the effect of citalopram (CIT), an SSRI, and IBU on IFNγ expression in mice. Figure 4 shows the effect of IBU on p11 expression in the presence and absence of treatment with CIT. In both figures, VEH represents the group given the control solution. Figure 3 Effect of citalopram and ibuprofen on IFNγ levels in the mouse frontal cortex Figure 4 Effect of ibuprofen on p11 expression in the brain in the presence and absence of citalopram treatment Note: For all graphs, data are presented as mean ± SEM; * indicates p < 0.05, # indicates p < 0.05 (effects of CIT), and ** indicates p < 0.05 (effects of IBU). Question According to the data presented in the passage, 5-HTR4 is a: A. protein kinase. B. tyrosine kinase receptor. C. ligand-gated ion channel. D. G protein-coupled receptor.

Native carbonic anhydrase also has a net charge of -2.9 at pH 8.0. Which chromatographic technique would most likely separate a mixture of native carbonic anhydrase from carbonic anhydrase photochemically modified by CCl3CO2H? A. Anion-exchange chromatography B. Cation-exchange chromatography C. Gas-liquid chromatography D. Size-exclusion chromatography

Solution: The correct answer is A. A. Because the passage states that native carbonic anhydrase has a net charge of -2.9 and the modified enzyme would have greater negative charge, anion-exchange chromatography can separate them as this technique separates proteins with different negative charges. B. The native and modified Enzymes both have net negative charge. In cation-exchange chromatography, both Enzymes would elute together in the void volume. C. Proteins degrade before they would vaporize. D. The molecular weights of the native and modified proteins are too close (< 1 kDa difference) to allow separation by size-exclusion chromatography.

As accustomed as we have become to the idea that scientists "construct" theories and "produce" explanations, and regardless of the controversies among scientists, the fact remains that they only disclose to us a world that came into being without the sciences or other human contributions. Galileo may have conceptualized and formalized the phases of Venus, but the phases themselves had manifestly always existed. Galileo's fabricated hypothesis simply became the acknowledged fact. By contrast, in conceptualizing technological projects, engineers produce fictions. The technology concerned does not, and by definition could not, exist, since it is in the project phase. This tautology frees the analysis of technological proposals from the burden of confirmation necessary in the analysis of scientific hypotheses. One might argue, of course, that Diesel did not create the principles he applied in his engine any more than Galileo created the astronomical principles he observed, and some would even contend that the engine was therefore as much beyond the control of Diesel as Venus was beyond the control of Galileo. Even so, few would seriously defend the proposition that the diesel engine had always existed and needed only to be discovered. In reference to technology, Platonism is considered an extreme philosophical stance. The rejection of Platonism means greater freedom for those who study machinery than for those who study nature. The big issues of reality and plausibility do not bother the former. Engineers may freely create fictions, since the projection of a technological possibility from the present, or from five or fifty years in the future, to a time t, is a part of their job. They invent a nonexistent means of transportation, with paper passengers, opportunities yet to be created, hypothetical places to be served (often to be themselves designed from scratch), new component industries, an assumed technological revolution. They are novelists, with one difference: Their project, although initially indistinguishable from a novel, will either remain a possibility in a file or be transformed into an object. At first, projects and the objects to which they pertain are indistinguishable. The two concepts circulate from office to office in the form of plans, memos, discussions, scale models, and occasional synopses. In this stage of signs, language, and text, people influence the object. But once the project is realized and the object real, it is people, outside their offices, who are influenced by it—a Copernican revolution. The gulf between the world of symbols and the world of things is then apparent. The R-312 is no longer a fiction that carries me away in transports of delight; it is a bus that transports me along the Boulevard Saint-Michel. Still, the creators of technology do not rigidly differentiate symbol from thing, project from object, the novel that excites speculation from the reality inscribed in the nature of things. For as the R-312 passes progressively from fiction to fact, its engineers repeatedly pass between the speculative and the practical realms. The capacity to be liberated from an exclusive concern from reality and to soar into unrealized potential is the quality that gives technological fiction a beauty that the literary novel, a form inherited from the naturalistic nineteenth century, has difficulty in approaching. Only a fiction that is capable of gaining or losing reality can do justice to engineers, those great unhonored figures of culture and history. A fiction with a variable structure—it is this flexibility to which we must aspire in tracking a technological project. Question According to social psychologists, people tend to respond to words and symbols as if they were the things to which they refer. What would the passage author be most likely to say about this tendency? A. It must be repeatedly overcome by engineers as a project progresses toward its physical realization. B. It accords with the distinction between the hypotheses of scientists and the proposals of engineers. C. It explains the failure to honor great engineers who have turned projects into objects. D. It implies an overemphasis on plans and working models in technological projects.

Solution: The correct answer is A. The author emphasizes that the beauty and appeal of a project before it results in the creation of a physical object is the project's quality as an imaginative fiction under the control of the engineer. The author also associates this conceptual stage with language and symbols: "In this stage of signs, language, and text, people influence the object" (paragraph 4). This suggests that, in the conceptual stage, it is best not to respond to the project as if it were a fixed object that already exists. For instance, the author compares the project to "A fiction with a variable structure" and states that "it is this flexibility to which we must aspire in tracking a technological project" (final paragraph).

Many blues musicians in the United States, particularly artists who grew up in the South during the first half of the twentieth century, experienced economic and other challenges and are often depicted as struggling artists with limited resources. At first glance, the Delta Blues Museum in Clarksdale, MS, seems not to portray blues artists in this conventional way. For instance, one exhibit chronicling the history of the blues includes a picture of Robert Johnson holding an acoustic guitar and wearing a fashionable pinstripe suit with a handkerchief neatly tucked in the front pocket. One of only two surviving photographs of Johnson, the picture was taken in a professional studio. The museum even contains a life-size mannequin of Muddy Waters dressed in an immaculate white suit and holding an expensive Gibson electric guitar. Beyond these visual representations of the artists as well-dressed and successful musicians, brief narratives from blues experts acknowledge the musicians' important contributions to American popular culture. Upon closer examination, however, these symbols of success are overshadowed by the museum's concerted efforts to construct what many people perceive as more "authentic" images of blues musicians. This strategy takes various forms. First, examples of blues artists' material struggles abound in the collection. In a memorial to Big Joe Williams, the guitarist is pictured playing his guitar on his porch. Although Williams is the focal point of the picture, the deteriorating porch and exterior wall, along with what appears to be a dirt driveway, suggest the musician's limited means. There are also a number of tattered instruments on display. Many of the exhibit's acoustic guitars, for example, are disfigured, reflecting the difficult and uncompromising lives of their former owners. The wooden body of Big Joe Williams's guitar, for example, is filled with scratches and nicks, the frets are worn, and the finish on the guitar neck is missing in several places, revealing a black undercoat. Visitors will also find well-used harmonicas and percussion instruments protected in a glass display case. Although technically "silent," the instruments play a song of the artist's history, craft, struggle, and legacy. While one cannot deny that many of these musicians were forced to survive in a world of poverty and grueling, labor-intensive employment, it is also true that some blues musicians, including B.B. King, Buddy Guy, Robert Cray, and others, amassed considerable personal fortunes. The museum's exhibits are constructed to satisfy the expectations of tourists who seek out images of what they perceive as an authentic blues culture. This display strategy not only works to legitimize and reinforce the image of the authentic blues singer, it also embodies larger marketing and promotional strategies designed to perpetuate the romantic vision of the Mississippi Delta as the mythical birthplace of the blues. For many blues tourists, the Delta serves as the last bastion of an authentic blues culture apparently untainted by the more commercial aspects of marketing and tourism. Despite this perception, several Southern states are capitalizing on the popularity of the blues and the potential financial windfall generated from tourists. According to ethnomusicologist Jeff Todd Titon, recent efforts reflect the "new blues tourism," an organized attempt to create a mediated experience for tourists ironically seeking an "authentic" and "genuine" blues experience. The new blues tourism is an example of niche tourism that capitalizes on the efforts of communities to accentuate their cultural heritage in an effort to increase their revenue from tourism as an industry. Question Suppose that studies have shown that niche tourists are often very knowledgeable about the subjects of their tourism. How would this information most likely affect passage arguments? A. It would complicate the claim about what tourists expect to find when they visit the Delta region. B. It would support the claim about the effect of museum displays on the image of authentic blues culture. C. It would have no impact on the arguments presented in the passage. D. It would weaken the claim about the effort of communities to accentuate their cultural heritage.

Solution: The correct answer is A. The passage clearly suggests that the "truth" of blues history is more complex and multi-faceted than the dominant images that feature the economic hardship of musicians and communities would have it. The passage says that tourists are "ironically seeking the 'authentic' and 'genuine' blues experience," even as this is somewhat cynically constructed for them (final paragraph). But, if tourists were actually very knowledgeable about the blues, they would be less likely to be seeking this dominant image—so the scenario in the question would complicate passage claims about what tourists are seeking. If visitors were very well informed, as this question indicates, then they would be less likely to take the exhibits simply at face value. The statement in the question is relevant to passage arguments about what tourists expect to discover when they visit the Delta region. The statement in the question is irrelevant to the claim about community efforts to accentuate heritage.

Two open flasks I and II contain different volumes of the same liquid. Suppose that the pressure is measured at a point 10 cm below the surface of the liquid in each container. How will the pressures compare? A. The pressures will be equal. B. Pressure in flask I will be less. C. Pressure in flask II will be less. D. The pressures cannot be compared from the information given.

Solution: The correct answer is A. The pressure at a point 10 cm below the surface of the liquid is the same in both flasks because the pressure is equal to the liquid density multiplied by the gravitational acceleration multiplied by 10 cm. The shape of the flasks doesn't matter. If one has a narrow mouth and the other has a wide mouth, it will not affect pressure under the surface.

Based on the reported Hill coefficient of 2.56, in what way do the MCS oligomers affect inhibition? A. As one MCS oligomer binds to the ATPase, it makes it easier for the others to bind, leading to inhibition. B. As one MCS oligomer binds to the ATPase, it makes it more difficult for the others to bind, leading to inhibition. C. A single MCS oligomer binds to the ATPase, leading to inhibition. D. MCS oligomers randomly bind to the ATPase, leading to inhibition.

Solution: The correct answer is A. The reported Hill coefficient of 2.56 indicates positive cooperativity because the value is greater than 1.0. Therefore, when one MCS oligomer binds to the ATPase, it makes it easier for others to bind. When there are sufficient MCS oligomers bound, they lead to inhibition of the ATPase.

The NADH:quinone oxidoreductase (Na+-NQR) is a transmembrane protein that catalyzes the reaction between NADH and ubiquinone coupled to the pumping of Na+ across the plasma membrane, resulting in a Na+ concentration gradient. The electron transport pathway in Na+-NQR is composed of four flavins (FAD, FMNc, FMNb, and riboflavin) and a [2Fe-2S] center, with electrons flowing in the direction: NADH → FAD → [2Fe-2S] → FMNc → FMNb → riboflavin → ubiquinone. Two electrons are transferred from NADH to FAD in the first step of the cycle, but all subsequent steps are one-electron transfers. Researchers were interested in observing whether Na+ has a thermodynamic effect on electron transport. Working with purified Na+-NQR from Vibrio cholerae, the researchers used spectroelectrochemistry to investigate the chemical changes that take place during electron transfer and how these changes are impacted by the presence of various cations. Na+-NQR was diluted to a final concentration of 0.75 mM in 0.150 M LiCl, NaCl, KCl, RbCl, or NH4Cl (each solution also contained redox active mediators) and placed in a glass instrument cell with CaF2 windows. The cell was equipped with two gold "grids," which served as the working electrodes. The applied potential was varied from +200 mV to −400 mV in 20 mV increments, and a visible spectrum was recorded at each potential after waiting 40 minutes. A computer was necessary to simulate the data since the individual spectral transitions overlap. Redox transitions were assigned based on the spectroscopic changes that took place at each potential. Some of the results and assignments are presented in Table 1. What functional group transformation occurs in the product of the reaction catalyzed by Na+-NQR? A. RC(=O)R → RCH(OH)R B. ROPO32- → ROH + Pi C. RC(=O)NHR'→ RCOOH + R'NH2 D. RC(=O)OR'→ RCOOH + R'OH

Solution: The correct answer is A. This is two-electron reduction of a ketone to an alcohol, which is the reaction catalyzed by Na+-NQR.

Cholera is an acute, diarrheal disease caused by infection of the intestine with the gram-negative, motile bacterium Vibrio cholerae. After colonizing the small intestine, V. cholerae secretes cholera toxin (CTX), a protein that ribosylates the Gsα subunit of a G protein, thereby inhibiting its GTPase activity. This causes the dysregulation of a cellular chloride ion channel, resulting in efflux of ions and water from the infected enterocytes into the intestinal lumen. Studies have implicated sodium bioenergetics in the pathogenesis of V. cholerae in humans. An electrochemical gradient of Na+ known as the "sodium motive force" provides V. cholerae with the energy for key functions. The gradient is predominantly established by the Na+-pumping NADH:quinone oxidoreductase (Na+-NQR) enzyme. Na+-NQR is a multi-substrate enzyme comprised of six distinct subunits designated A-F (Table 1) that are encoded within the same operon. In a process similar to proton pumping by Complex I of the electron transport chain, Na+-NQR couples the movement of electrons from an NADH donor with ion transport. Researchers investigated the kinetic features of Na+-NQR. Figure 1 shows a double reciprocal plot of 1/V0 versus 1/concentration of one substrate, NADH, at three concentrations (1X, 2X, 3X) of the second substrate, quinone. Reactions were performed in conditions where NaCl was saturating. Figure 1 Double reciprocal plot of Na+-NQR activity at three concentrations (1X, 2X, 3X) of quinone Question What is the most likely effect of adding a sodium ionophore to a culture of V. cholerae? A. Decreased activity of Na+-NQR B. Decreased production of ATP C. Decreased pH of the periplasm D. Decreased consumption of O2

Solution: The correct answer is B. A sodium ionophore does not interfere with the function of Na+-NQR, but it degrades the sodium gradient (sodium motive force) that is established by the action of Na+-NQR. Ionophores are compounds that bind to ions and facilitate their movements across membranes. A sodium ionophore would collapse the sodium gradient (sodium motive force) that is established by the action of Na+-NQR, resulting in decreased production of ATP. V. cholerae uses an electrochemical gradient of Na+, not of protons, to generate ATP. Therefore the pH of the periplasm is not affected. Since sodium ionophores degrade the electrochemical gradient required for ATP synthesis, they cause a decrease in ATP levels. To compensate for this event, V. cholerae is likely to increase the flux of electrons to the respiratory chain, which results in increased, not decreased, oxygen consumption.

In which phase(s) will the MCS precursor be predominantly found after the extraction step? The MCS precursor will: A. be found in the aqueous layer. B. be found in the tert-butyl methyl ether layer. C. be distributed equally between the aqueous layer and the tert-butyl methyl ether layer. D. form a precipitate between the aqueous and tert-butyl methyl ether layers.

Solution: The correct answer is B. A. According to the passage, the MCS precursor is lipophilic, so it is not water soluble. B. The passage described the MCS precursor as being lipophilic, which means that it would not dissolve as readily in the aqueous layer. Therefore, it should be found in the tert-butyl methyl ether layer, which is hydrophobic. C. According to the passage, the MCS precursor is lipophilic, so it prefers to dissolve in organic solvents. D. The MCS precursor should dissolve in the organic layer.

A 2 kg mass and a 5 kg mass are connected by a massless cord suspended over a massless and frictionless pulley. If the acceleration due to gravity is g, what will be the acceleration of the masses after they are released from rest? A. 2g/7 B. 3g/7 C. 5g/7 D. g

Solution: The correct answer is B. According to Newton's second law, the net force acting on the 5-kg mass is given by the expression Fnet= 5 kg × a1 = 5 kg × g - T, where a1 is the acceleration after the release and T is the tension in the cord. The net force acting on the 2-kg mass is given by the expression Fnet= 2 kg × a2 = 2 kg × g - T. Because the two masses move simultaneously but in opposite directions after they are released, a1 = -a2 = a. Substituting the expression T = 5 kg × (g - a) into the equation of motion of the 2-kg mass yields -2 kg × a = 2 kg × g - 5 kg × (g - a) = -3 kg × g + 5 kg × a. Then 7 kg × a = 3 kg × g, hence a = 3g/7.

Weber's characteristics of an ideal bureaucracy suggest that most formal organizations will: A. train employees to conduct a variety of tasks. B. select employees based on technical qualifications. C. require employees to seek consensus in decisions. D. evaluate employees based on individualized criteria.

Solution: The correct answer is B. According to Weber's conceptualization of ideal bureaucracy, a formal organization requires specialization in a limited number of tasks, rather than completing a variety of tasks. Employment in a formal organization is based on technical qualifications; therefore, this option is consistent with the characteristics of an ideal bureaucracy. Decisions in ideal bureaucracies are based on an organizational hierarchy instead of consensus among employees. Evaluation of performance and skills in ideal bureaucracies are not based on individualized criteria, but on standardized rules and procedures.

The prevailing approach to improving population health emphasizes "shifting the mean" through prevention efforts that target large groups at high risk for particular conditions, or through mass interventions that encourage small but universal changes in individual behavior. This approach encourages the search for "blockbuster" public health interventions that can have the largest effects on determinants of population health and individual behavior. New business models, however, demonstrate that selling small quantities of many "niche" items can be more profitable than selling a few blockbuster items. In The Long Tail, Chris Anderson argues that niche markets—subsets of consumers interested in particular products—are more accessible today than ever, and that although the demand for any particular niche-focused product will be limited, there are so many niches that together these products make up a huge market. He mentions a large online bookstore, in which half of the top 10,000 books sold less than one copy per quarter. Understanding how and why businesses profit from this "long tail" of niche products (in other words, focusing on consumers at the ends of the distribution curve) has the potential to transform our thinking about strategies to improve public health. Health messages can be thought of as products targeted to specific subgroups of the population, many of which bear a disproportionate burden of disease because of heightened exposure to risk or unequal access to beneficial or health-promoting resources. Such population subgroups might include some racial and/or ethnic minorities, populations with low income, and those without health insurance. Focusing on vulnerable populations could work to complement, rather than replace, a population approach. The number and complexity of niche markets increase exponentially when we consider how certain illnesses and preventive services affect different population subgroups, with different constellations of demographic, geographic, and health status risk factors. Approaches might be targeted to groups as diverse as migrant farmworkers in rural communities, parents of children with asthma, and Alaskan natives aged 50 years and older. Creating effective, tailored health resources for this near-infinite number of combinations of subgroups and health issues is a daunting task. Traditionally, local organizations have created resources targeted to particular users, but they are unlikely to have the kind of funding, capacity, and infrastructure that larger organizations do. Furthermore, because there are few mechanisms for efficient sharing among niche-serving organizations, duplication is bound to occur. One study identified 116 different types of printed cancer education materials that targeted African Americans. The Internet has been invaluable in facilitating the distribution of niche products, making it easy for consumers to find niche products through the use of filters, recommendation systems, and ratings. The opportunity to sample an unfamiliar product before buying it—to read a chapter from a book, for instance—lowers the consumer risk. Finally, the ability to customize a product to a user's needs or preferences can increase its appeal. In order to create health communication materials targeted to specific populations, organizations can take advantage of Internet-based resources. The Make It Your Own (MIYO) system is an online tool that helps users create health communication materials for the specific populations they serve. Users "build" materials by choosing from a menu of evidence-based approaches recommended by the Guide to Community Preventive Services, then customize them by choosing from a library of images, messages, and graphic designs. MIYO renders their creations into electronic documents that can be printed, e-mailed, texted, used online, or distributed in other ways to target audiences. This approach might work as well for other evidence-based public health solutions, such as campaigns, social marketing, behavioral interventions, or worksite and/or school-based programs. Question Suppose that people who live in low-income neighborhoods are less likely than people in affluent neighborhoods to have access to community recreational facilities and lighted sidewalks. How would this affect passage claims? A. It would challenge claims about the "long tail" approach to public health. B. It would support passage claims about access to beneficial resources. C. It would undermine claims about the value of "blockbuster" interventions. D. It would reinforce claims about the funding, capacity, and infrastructure of local organizations.

Solution: The correct answer is B. If anything, the scenario described in the question would support the long tail approach, because the long tail approach targets groups with specific needs, for whom broadly targeted approaches may be ineffective or inappropriate. The passage refers to the fact that some population subgroups have "unequal access to beneficial or health-promoting resources" (paragraph 3), which is exactly what the question refers to. If anything, the scenario described in this question would support those claims, as the point of long-tail approaches is to reach groups who may "bear a disproportionate burden of disease because of heightened exposure to risk or unequal access to beneficial or health-promoting resources" (paragraph 3). The statement in the question is irrelevant to passage claims about the funding, capacity, and infrastructure of local organizations.

Cow's milk allergy (CMA) and lactose intolerance both result from dietary exposure to cow's milk and are often confused. CMA is caused by an abnormal inflammatory response to one or more proteins in cow's milk. Although more than one mechanism appears to be involved in generating this response, the antibody-mediated response is the best understood. Development of the antibody-mediated response occurs in two stages, the first being the generation of an abnormal immune response during initial exposure to milk proteins and the second being the generation of an inflammatory response upon subsequent exposure. Symptoms of antibody-mediated CMA may include hives and respiratory difficulty. Anaphylactic shock rarely occurs but can be fatal if not treated immediately. Lactose intolerance, also known as lactase deficiency, is a condition that results from insufficient synthesis of the enzyme lactase, which converts lactose into glucose and galactose. Although all healthy newborns produce sufficient levels of lactase, two distinct phenotypes exist in adults: lactase persistence (LP) (includes heterozygotes) and lactase non-persistence (LNP). LP adults continue to produce lactase into adulthood, whereas LNP individuals do not. It has been suggested that the LP phenotype is the result of a mutation event that coincided with the domestication of dairy animals thousands of years ago in areas such as northwestern Europe and within some Afro-Arabian nomadic populations. In Northwestern Europeans, sets of alleles located closely together on the same chromosome (haplotypes) associated with the LP phenotype contain several single nucleotide polymorphisms (SNPs). However, only one appears to be directly responsible for this phenotype; the others are silent. By comparison, several different SNPs appear to be directly responsible for the LP phenotype in Afro-Arabian LP-associated haplotypes. Question Lactase can be classified as which type of enzyme? A. Isomerase B. Hydrolase C. Transferase D. Oxidoreductase

Solution: The correct answer is B. Isomerases are Enzymes that restructure the chemical formula of a compound. They do not break down the chemical bound in a disaccharide such as lactose. The passage notes that lactase breaks down lactose to glucose and galactose. Glycosidic linkages in disaccharides are cleaved via a hydrolysis reaction; therefore, lactase is classified as a hydrolase. Transferases are Enzymes that transfer chemical groups between compounds. They do not break down the chemical bound in a disaccharide such as lactose. Oxidoreductases are Enzymes that catalyze the removal of electrons and hydrogen atoms. They do not break down the chemical bound in a disaccharide such as lactose.

Cholera is an acute, diarrheal disease caused by infection of the intestine with the gram-negative, motile bacterium Vibrio cholerae. After colonizing the small intestine, V. cholerae secretes cholera toxin (CTX), a protein that ribosylates the Gsα subunit of a G protein, thereby inhibiting its GTPase activity. This causes the dysregulation of a cellular chloride ion channel, resulting in efflux of ions and water from the infected enterocytes into the intestinal lumen. Studies have implicated sodium bioenergetics in the pathogenesis of V. cholerae in humans. An electrochemical gradient of Na+ known as the "sodium motive force" provides V. cholerae with the energy for key functions. The gradient is predominantly established by the Na+-pumping NADH:quinone oxidoreductase (Na+-NQR) enzyme. Na+-NQR is a multi-substrate enzyme comprised of six distinct subunits designated A-F (Table 1) that are encoded within the same operon. In a process similar to proton pumping by Complex I of the electron transport chain, Na+-NQR couples the movement of electrons from an NADH donor with ion transport. Which enzyme of the citric acid cycle is NOT directly involved in generation of the dinucleotide required for Na+-NQR activity? A. Malate dehydrogenase B. Succinate dehydrogenase C. Isocitrate dehydrogenase D. Α-Ketoglutarate dehydrogenase

Solution: The correct answer is B. The passage notes that Na+-NQR requires NAD+/NADH for its activity. Malate dehydrogenase does require NAD+/NADH. The passage notes that Na+-NQR requires NAD+/NADH for its activity. Among the options, only the conversion of succinate to fumarate by succinate dehydrogenase which generates FADH2, does not require NAD+/NADH. Malate dehydrogenase, isocitrate dehydrogenase and α-Ketoglutarate dehydrogenase all generate NADH within the citric acid cycle. The passage notes that Na+-NQR requires NAD+/NADH for its activity. Isocitrate dehydrogenase also requires NAD+/NADH. The passage notes that Na+-NQR requires NAD+/NADH for its activity. α-Ketoglutarate dehydrogenase also requires NAD+/NADH.

Research has implicated stress as a contributing factor to cognitive decline in aging. Stress-related hormones have been found to affect the hippocampus. Studies on animals have shown that chronic increases in stress-related hormones are associated with reduced dendritic spines, decreased long-term potentiation, and reduced neurogenesis in the hippocampus. Studies on humans show that people who have experienced posttraumatic stress disorder have reduced hippocampal volume. In contrast to stress, exercise has been shown to benefit learning and memory functioning in aged animals. A study was designed to investigate the relative effects of exercise and lifetime stress on hippocampal volume and cognitive functioning in humans. Participants were selected from older adults. To assess lifetime stress, participants were given a list of stressors and were asked to indicate the number of times they experienced each. To assess exercise engagement, they completed a questionnaire regarding their cardiovascular activity for the past ten years. To assess cognitive functioning, they were presented with a list of fifteen items categorizable as animals, clothing, and furniture. After participating in a 2-minute distraction task, they were asked to recall as many of the items as possible and categorize them. The volume of the hippocampus was also assessed for each participant. Based on the exercise assessment, participants were grouped into "high exercise" or "low exercise" categories. The results of the study showed that lifetime stress was negatively correlated with hippocampal volume and memory for low exercise participants, but no correlation was found between these variables for the high exercise participants. Question Based on the passage, participation in which study is most likely to be associated with a decrease in hippocampal volume in rats? A study on: A. the extinction of conditioned responses B. learned helplessness and avoidance learning C. the effectiveness of stimulants as reinforcers D. instinctive drift and classical conditioning

Solution: The correct answer is B. The passage states that, "Studies on animals have shown that chronic increases in stress-related hormones are associated with reduced dendritic spines, decreased long-term potentiation, and reduced neurogenesis in the hippocampus. Studies on humans show that people who have experienced posttraumatic stress disorder have reduced hippocampal volume." Extinction of conditioned responses does not require exposure to a stressor and thus is not relevant to the passage discussion of changes to hippocampal volume. Avoidance learning occurs when the individual responds to prevent the presentation of an aversive stimulus, while learned helplessness is a behavioral and physiological state that occurs as a result of exposure to uncontrollable aversive consequences. The inescapable aversive stimulus is a chronic stressor which would be predicted to be associated with decreased hippocampal volume. Stimulants are psychoactive substances which increase central nervous system activity. As they are not stressors, passage information does not support them being associated with a decrease in hippocampal volume. Instinctive drift refers to the interference of innate, species-specific behaviors with continued performance of a learned response. As this is not a stressor, it is not relevant to the passage discussion of decreased hippocampal volume.

The resting potential of a neuron is primarily a result of the: A. release of neurotransmitters from the axon. B. distribution of ions across the plasma cell membrane. C. action of neurotransmitters on the postsynaptic receptor. D. active transport of Ca2+ ions across the plasma cell membrane.

Solution: The correct answer is B. Release of neurotransmitters will most likely induce a local potential, which is a shift from the resting potential of a neuron. Membrane potential refers to the difference in charge distribution on opposing sides of a cell membrane. Within a neuron, the resting potential is determined by the normal, uneven distribution of ions between the outside and the inside of a cell. Neurotransmitters at the post-synaptic membrane often generate current that will produce a local potential. A local potential is a shift from the resting potential of a neuron. Ca2+ pumps actively transport Ca2+ out of a neuron. However, intracellular Ca2+ primarily controls neurotransmitter release, not the resting potential of a neuron.

When the covalent attachment to alliinase is broken, PLP is still held rigidly in the active site by a salt bridge and a π-stacking interaction. These interactions are most likely provided by the side chains of which amino acids? (Note: The salt bridging amino acid is listed first.) A. Asp and Tyr B. Glu and Ser C. Arg and Tyr D. Lys and Ser

Solution: The correct answer is C. A. Although Tyr can form a π-stacking interaction, Asp has a negatively charged side chain that will repel, not attract, the phosphate in PLP. B. Glu has a negatively charged side chain, which will repel, not attract, the negatively charged phosphate in PLP. Lacking an aromatic ring, Ser is not capable of a π-stacking interaction. C. PLP has a negatively charged phosphate that can make a salt bridge with the positively charged side chain of Arg, and the aromatic ring in the side chain of Tyr can form a π-stacking interaction. D. Although the positively charged side chain of Lys can form a salt bridge with the phosphate of PLP, Ser does not contain an aromatic ring for a π-stacking interaction.

The researchers purified the hMPRα with two successive rounds of chromatography that exploited each of the tags. hMPRα was then extracted from the membranes using n-decyl-β-D-maltopyranoside, Compound 2. What structural feature(s) is(are) most important to the functioning of this compound as described in the passage? A. Specific configuration of numerous chirality centers B. Multiple hydrolysable linkages C. Combination of large hydrophobic and hydrophilic regions D. Presence of a reducing sugar

Solution: The correct answer is C. A. Chirality is important for specific binding to other compounds. This is not a requirement of a detergent. B. Multiple hydrolysable linkages would facilitate metabolism. Compound 2 was a detergent used to help isolate membrane proteins. C. Compound 2 was used as a detergent. It liberated a protein from a membrane so that it might be isolated. The combination of large hydrophilic and hydrophobic regions allows Compound 2 to function in this capacity. D. The presence of a reducing sugar makes the compound susceptible to oxidation and imparts aqueous compatibility. It does not provide all the necessary components of a functioning detergent.

Enantiomers can exhibit a difference in which chemical or physical property? A. Density B. Boiling point C. Smell D. IR spectrum

Solution: The correct answer is C. A. Enantiomers will not display different densities. B. The boiling points of enantiomers are identical, and they cannot be separated by distillation. C. Enantiomers have the same physical and chemical properties. They differ only in their three dimensional arrangement of atoms and their interactions with other chiral molecules. They can differ in their smell due to interacting differently with chiral odorant receptors. D. The IR spectra of enantiomers are identical when a normal light source is used. Circularly polarized light will potentially illustrate differences.

Cow's milk allergy (CMA) and lactose intolerance both result from dietary exposure to cow's milk and are often confused. CMA is caused by an abnormal inflammatory response to one or more proteins in cow's milk. Although more than one mechanism appears to be involved in generating this response, the antibody-mediated response is the best understood. Development of the antibody-mediated response occurs in two stages, the first being the generation of an abnormal immune response during initial exposure to milk proteins and the second being the generation of an inflammatory response upon subsequent exposure. Symptoms of antibody-mediated CMA may include hives and respiratory difficulty. Anaphylactic shock rarely occurs but can be fatal if not treated immediately. Lactose intolerance, also known as lactase deficiency, is a condition that results from insufficient synthesis of the enzyme lactase, which converts lactose into glucose and galactose. Although all healthy newborns produce sufficient levels of lactase, two distinct phenotypes exist in adults: lactase persistence (LP) (includes heterozygotes) and lactase non-persistence (LNP). LP adults continue to produce lactase into adulthood, whereas LNP individuals do not. It has been suggested that the LP phenotype is the result of a mutation event that coincided with the domestication of dairy animals thousands of years ago in areas such as northwestern Europe and within some Afro-Arabian nomadic populations. In Northwestern Europeans, sets of alleles located closely together on the same chromosome (haplotypes) associated with the LP phenotype contain several single nucleotide polymorphisms (SNPs). However, only one appears to be directly responsible for this phenotype; the others are silent. By comparison, several different SNPs appear to be directly responsible for the LP phenotype in Afro-Arabian LP-associated haplotypes. Question Based on the information in the passage, the mutation that causes the LP phenotype is most likely located in: A. an intron within the lactase gene. B. the coding sequence of the lactase gene. C. an enhancer sequence of the lactase gene. D. the stop codon at the end of the lactase gene.

Solution: The correct answer is C. Although introns might have regulatory functions, mutations to promoter and enhancer regions most specifically alter gene expression. A mutation in the coding region is most likely associated with a mutated enzyme, which is not the case with the LP. Instead, lactase expression is altered during LP. The enhancer is a DNA region that is able to bind transcriptional activators in order to increase the expression of a particular gene. Since LP is caused by deficient lactase synthesis, this is the region most likely targeted by the mutation. Specifically, the mutation likely makes it more difficult for transcriptional activators to bind an enhancer sequence. A mutation affecting the STOP codon would result in a mutated enzyme, which is not the case in LP.

If only [I] is increased, then [ESI] or [EI] increases. This is an example of: A. the Bose-Einstein Principle. B. the Heisenberg Uncertainty Principle. C. the Le Châtelier's Principle. D. the Pauli Exclusion Principle.

Solution: The correct answer is C. Le Châtelier's Principle states that in a reversible process, the application of stress to the system will cause the system to respond in a way that will relieve this stress. In this case, the reversible process is E + I forming EI or ES + I forming ESI. In either case, increasing [I] induces stress of the system, and the system relieves that stress by converting I to either more EI or ESI.

Which biochemical technique requires a pH gradient? A. Limited proteolysis B. Southern blotting C. Isoelectric focusing D. SDS-PAGE

Solution: The correct answer is C. Proteolysis involves the cleavage of peptide bonds and does not require a pH gradient. Southern blotting is a technique to identify specific DNA fragments and does not require a pH gradient. Isoelectric focusing separates proteins based on their pIs. The technique uses an electric field and a pH gradient which causes proteins to stop moving at a pH equal to their pI. SDS-PAGE is a technique to separate proteins based on their size and does not require a pH gradient.

Which membrane transporter is electrogenic and translocates a net charge across the membrane? A. Na+− H+ exchanger B. Na+−C- cotransporter C. Na+−glucose cotransporter D. GLUT2 facilitative glucose transporter

Solution: The correct answer is C. The Na+-H+ exchanger is an antiporter in which the transport of one Na+ is coupled with the transport of one H+ in the opposite direction. This results in no net translocation of charge. The Na+-Cl- cotransporter transports one Na+ and one Cl- in the same direction. Therefore, there is no net movement of charge and this is an electroneutral process. The Na+-glucose cotransporter transports Na+ cations and glucose into the cell. This process is electrogenic, as it results in the net movement of positively charged molecules into the cell. As glucose is not a charged molecule, GLUT2 activity will not be associated with the net movement of charged molecules. Consequently, GLUT2 activity represents an electroneutral transport process.

Occupational stress has been recognized as one of the most significant workplace health hazards for employees in the United States and other developed countries. In the short term, stress can lead to emotional distress, stomach disorder, headaches, sleeplessness, and loss of energy; in the long term, it can contribute to serious illness and even premature death, most likely due to cardiovascular disease. Occupational stress costs U.S. businesses more than $150 billion per year because of absence, lost productivity, and health costs. Furthermore, occupational stress seems to be endemic to the modern workplace, as surveys have shown that a large proportion of workers report feeling highly stressed at work. There are a number of workplace factors, called job stressors, that make jobs stressful. Some stressors concern the nature of the job and job tasks. For example, jobs with heavy workloads requiring long periods of attention and jobs that are highly repetitive and boring will likely be perceived as stressful. Other stressors concern interpersonal relationships at work, such as conflicts with co-workers or abusive behavior by supervisors. Finally, there are stressors in the organizational context, such as having insufficient resources to do the job or unfair payment systems. One of the most important factors in determining the level of occupational stress experienced is the perception of control. Control can be over any aspect of work, including location, scheduling, and how tasks are done. Jobs differ tremendously in the amount and type of control they allow employees. At one extreme is factory work in which the employee must work at precisely determined times, performing specified tasks at intervals determined by a machine. At the other extreme are high-level management positions in which tasks can be done at any place, at any time, and in almost any manner employees see fit. Throughout the workday, employees experience and perceive conditions and events, most of which are typically benign and paid little attention. Certain events, however, are perceived and interpreted as somehow threatening to physical or psychological well-being—these are the perceived job stressors. The stressors result in negative emotional reactions, perhaps most commonly anger or anxiety. These emotions lead to strains, both behaviors and physical conditions associated with stress. Perceived control is an important element at all stages of this process. Job stressors can include anything that a person finds threatening, including the amount of work and work demands, constraints that interfere with work or prevent employees from getting their work done, interpersonal conflicts among employees, and uncertainty about tasks. Behavioral strains consist of actions people take to cope with stressors and the associated emotions. They can be constructive acts that successfully deal with stressors or acts that are destructive to the individual and the employer. Physical strains are related to both the fatigue of hard work and the physiology of negative emotion. Both kinds of physical strains can increase physiological arousal, resulting in elevated blood pressure and heart rate, as well as secretion of so-called stress hormones, such as adrenaline, into the bloodstream. In the short term, such physiological changes can result in minor physical symptoms, such as headache or upset stomach. Chronic elevation of heart rate and blood pressure can contribute to more serious health conditions and ultimately heart disease in some individuals. Compared with individuals who perceive they have low control, individuals who perceive they have high control will be less likely to interpret the environment as stressful, will have lower negative emotional responses, and will exhibit less strain. Question Based on the passage, an employee's heavy smoking could be considered to be: A. an occupational stressor for the smoker. B. a buffer between control and stress. C. a destructive behavioral strain. D. a constructive coping behavior.

Solution: The correct answer is C. The author defines occupational stressors, or job stressors as "anything that a person finds threatening, including the amount of work and work demands, constraints that interfere with work or prevent employees from getting their work done, interpersonal conflicts among employees, and uncertainty about tasks" (paragraph 5). The employee's heavy smoking would be a behavioral response to the occupational stressor, not a stressor of the job itself. The author explains that the employee's degree of "perceived control" over any aspect of work affects their level of stress (paragraph 3). But the author does not describe actions as "buffers between control and stress," nor is there any reason to believe that smoking would function in this way. The author explains that "Behavioral strains consist of actions people take to cope with stressors and the associated emotions. They can be constructive acts . . . or acts that are destructive to the individual and the employer" (paragraph 5). As heavy smoking is clearly harmful to the individual, and potentially to their employer, if they become sick, and is often used as a coping behavior," the smoking would be an example of a destructive behavioral strain. Because heavy smoking is very well-known to present serious health risks, calling this behavior a "constructive coping behavior" is highly implausible.

In the 1890s French artist Claude Monet devoted most of his time to painting the same subject, again and again, often from the exact same position—but in different kinds of light and in different seasons. These works were first exhibited together as each group was completed, and many of Monet's admirers at the time hoped—as Monet himself did—that some of the series could be kept together. Instead they were sold to collectors all over the world, a dispersion that evokes the breaking up and scattering of the panels of so many Renaissance altarpieces. Monet's series works were never exhibited together again in quantity until a 1990 exhibition at the Art Institute of Chicago. Hanging at right angles to each other in a corner of that exhibition were two paintings of Norway's Mount Kolsaas, one of which is unfinished. A comparison of the two helps us to see what makes these paintings magical. While the unfinished picture is immediately pleasing, one needs to turn to the finished picture to find a surface swarming with tiny details, each related to the others in a kind of organic interdependence. It is because this work lives in such details that the paintings' deepest beauty does not survive in reproductions; the work must be seen up close, slowly, canvas by canvas. Viewed this way, the surface of each painting suggests a wealth of inner movement, as the eye progresses from one tiny colored splotch or line to the next, as if viewing some mysterious microscopic living world. Yet there is much more than sensual pleasure here. As is the case with a number of other nineteenth- and early twentieth-century paintings, each work contains a knot of paradoxes. The physical world is present in these paintings with stunning immediacy. But at the same time, one cannot resist the feeling that each work is as carefully arranged, composed, and synthetically created as the gardens Monet cultivated at his home in Giverny. The overall compositions are often very simple, yet they seem carefully selected and perfectly balanced—too perfect to be an accident of nature. A related paradox can also be found not only in Monet's work, but in the work of a number of his contemporaries, particularly Cezanne. These artists apply paint in varying degrees of thickness to produce relief effects. This slight three-dimensionality heightens the viewer's sense of the physicality of the object depicted, while making it even more apparent that one is viewing pigment. We live in a culture cluttered with objects, with a surfeit of media noise and a glut of images that encourage only the most superficial visual impressions. If seen with care, Monet's work can help inspire a renewed vision. Rather than offering us wall decorations whose effects never change, he offers us pictures that have some of the completeness, complexity, and mutability of a living being. To those who perceive all else on our planet in hierarchical terms, Monet offers images that represent all parts of the world, from trees to rocks to the polluted smoke over London, as equally alive. To a civilization whose hypertrophied industrialization is steadily breaking down all the life-producing interconnections nature built up over millions of years, he offers an image of birds, boats, cliffs, sky, air, and light as all part of the same ecosystem. Indeed, it would not be going too far to say that these works offer a genuinely ecological vision. Question Which statement, if assumed to be true, most challenges the author's claim regarding reproductions of Monet's art? A. Many reproductions of Monet's art are indistinguishable from the originals to the casual viewer. B. Reproductions of paintings are not necessarily photographic reproductions. C. A good reproduction can heighten detail. D. Many reproductions of Monet's art sell for very high prices.

Solution: The correct answer is C. The author's comment: "It is because this work lives in such details that the paintings' deepest beauty does not survive in reproductions" (paragraph 3) suggests that reproductions lack detail, which challenges the option that claims that reproductions "heighten" detail. That reproductions may be indistinguishable from originals "to the casual viewer," who may not know very much about "details" of art does not directly challenge this comment. Whether or not the reproductions of which the author speaks are photographic reproductions is irrelevant to the author's claim about reproductions. "It is because this work lives in such details that the paintings' deepest beauty does not survive in reproductions" (paragraph 3) suggests that reproductions lack detail, which makes this option correct as it challenges this implication. Price is irrelevant to the author's claim that reproductions of Monet's art lack detail.

In the 1890s French artist Claude Monet devoted most of his time to painting the same subject, again and again, often from the exact same position—but in different kinds of light and in different seasons. These works were first exhibited together as each group was completed, and many of Monet's admirers at the time hoped—as Monet himself did—that some of the series could be kept together. Instead they were sold to collectors all over the world, a dispersion that evokes the breaking up and scattering of the panels of so many Renaissance altarpieces. Monet's series works were never exhibited together again in quantity until a 1990 exhibition at the Art Institute of Chicago. Hanging at right angles to each other in a corner of that exhibition were two paintings of Norway's Mount Kolsaas, one of which is unfinished. A comparison of the two helps us to see what makes these paintings magical. While the unfinished picture is immediately pleasing, one needs to turn to the finished picture to find a surface swarming with tiny details, each related to the others in a kind of organic interdependence. It is because this work lives in such details that the paintings' deepest beauty does not survive in reproductions; the work must be seen up close, slowly, canvas by canvas. Viewed this way, the surface of each painting suggests a wealth of inner movement, as the eye progresses from one tiny colored splotch or line to the next, as if viewing some mysterious microscopic living world. Yet there is much more than sensual pleasure here. As is the case with a number of other nineteenth- and early twentieth-century paintings, each work contains a knot of paradoxes. The physical world is present in these paintings with stunning immediacy. But at the same time, one cannot resist the feeling that each work is as carefully arranged, composed, and synthetically created as the gardens Monet cultivated at his home in Giverny. The overall compositions are often very simple, yet they seem carefully selected and perfectly balanced—too perfect to be an accident of nature. A related paradox can also be found not only in Monet's work, but in the work of a number of his contemporaries, particularly Cezanne. These artists apply paint in varying degrees of thickness to produce relief effects. This slight three-dimensionality heightens the viewer's sense of the physicality of the object depicted, while making it even more apparent that one is viewing pigment. We live in a culture cluttered with objects, with a surfeit of media noise and a glut of images that encourage only the most superficial visual impressions. If seen with care, Monet's work can help inspire a renewed vision. Rather than offering us wall decorations whose effects never change, he offers us pictures that have some of the completeness, complexity, and mutability of a living being. To those who perceive all else on our planet in hierarchical terms, Monet offers images that represent all parts of the world, from trees to rocks to the polluted smoke over London, as equally alive. To a civilization whose hypertrophied industrialization is steadily breaking down all the life-producing interconnections nature built up over millions of years, he offers an image of birds, boats, cliffs, sky, air, and light as all part of the same ecosystem. Indeed, it would not be going too far to say that these works offer a genuinely ecological vision. Question "The small streaks of color in Monet's paintings give one the feeling they were selected as much for their harmoniousness in relation to each other as for their fidelity to the actual scene." What is the relevance of this comment to the material about paradoxes presented in the passage? A. It challenges the first paradox. B. It challenges the second paradox. C. It provides a supporting example of the first paradox. D. It provides a supporting example of the second paradox.

Solution: The correct answer is C. The first paradox is about careful arrangement, which this comment doesn't address. The second paradox is about paint thickness, which this comment doesn't address. The author describes the first paradox: "The overall compositions are often very simple, yet they seem carefully selected and perfectly balanced—too perfect to be an accident of nature" (paragraph 4). This comment, about the "selection" of the color streaks in the paintings and the idea that they are both faithful to the reality of nature and yet ideally "harmonious" with each other supports the first paradox: a tension between "balance" and the messier reality of nature. The second paradox is about paint thickness, which this comment about the "harmonious" relation of the streaks of color in Monet's work does not provide a supporting example for.

Two theories of membrane structure are discussed below. Unit Membrane Model Phospholipid molecules are the most abundant type of lipids in cell membranes. Each consists of a nonpolar, hydrophobic tail, and a polar, hydrophilic head. The phospholipid chains orient themselves to form a bilayer with the tails pointed inward and the hydrophilic heads lined up on both sides of the bilayer. An extended monomolecular layer of protein coats both the outside of the membrane and the inside of the bilayer, but the protein does not penetrate the bilayer. When thin slices of membranes were examined with an electron microscope, three layers were seen: two electron-dense layers, with one wider layer between them. It was believed that the electron-dense layers represented proteins, and the lighter area represented lipids. Fluid Mosaic Model The structure of the fluid mosaic membrane is a bilayer of phospholipid molecules with proteins inserted into the bilayer. Hydrophilic regions of both the lipids and proteins are found on the outside surface, while the hydrophobic regions of both types of molecules are found on the inside surface. Because lipids are not fixed rigidly in the membrane, the membrane is capable of fluid movement. The theory that the proteins penetrate the lipid layer is supported when membranes are split along the middle of the lipid layer. When the top half is peeled back, small bumps can be seen on the remaining surface. These are assumed to be proteins. Question Which of the following observations would invalidate the Unit Membrane Model? A. When a thin section of membrane is observed using a microscope at high magnification, two layers of phospholipid heads are observed. B. Thermodynamic measurements indicate that the phospholipid heads are exposed to water. C. When a membrane is frozen and then split from surface to surface, proteins are observed within the hydrocarbon chains. D. Thermodynamic measurements indicate that the phospholipid tails are hidden inside the membrane, away from exposure to water.

Solution: The correct answer is C. This should be seen as proof of the presence of the phospholipid bilayer. The Unit Membrane Model indicates the presence of a phospholipid bilayer. Based on the description of the Unit Membrane Model, the phospholipid heads are hydrophilic, and are therefore expected to face water. According to the Unit Membrane Model, the proteins form a monolayer on the outer and inner surfaces of the phospholipid bilayer. Thus, when this bilayer is split, there should not be proteins observed within hydrocarbon chains. Instead, the proteins should be equally separated by the split. The presence of the hydrophobic tails buried within the phospholipid bilayer is described in the Unit Membrane Model.

Consider an experiment that consists of two ionic solutions separated by a membrane that contains a ligand-gated potassium channel. The lack of current generation in response to addition of ligand is explained by: lack of potassium in either solution. the presence of potassium in only one solution. equal concentrations of potassium in the two solutions. A. I only B. I and II only C. I and III only D. II and III only

Solution: The correct answer is C. If there are equal concentrations of potassium in the two ionic solutions, it follows that there is no net movement of ions across the channel and thus no current generation. The presence of potassium in only one solution results in its movement to the other side, thus generating a current. Lack of current means no net movement of ions, which only happens when the concentration of ions is the same on both sides of the membrane or there are no ions present that the channel is specific for (K+). If only one of the solutions contains potassium, the ion will move to the other solution to create a concentration equilibrium, thus generating a current.

The microbiome has been investigated for its possible link to non-hereditary diseases. Crohn's disease (CD) is a non-hereditary chronic inflammatory condition that may affect any part of the gastrointestinal (GI) tract. Causes for CD have not been defined to date; however, research has shown that the profile of the GI tract microbiome is different in healthy versus CD‑affected individuals. Therefore, researchers hypothesized that differences in bacterial distribution and the host immune response to GI tract bacteria might play a role in the establishment and progression of the disease. GI tract bacteria digest dietary fibers and convert them into butyrate, propionate, and acetate. These three molecules modulate the innate immune system response by attenuating the inflammatory response to GI tract commensal bacteria. Furthermore, butyrate is a major source of energy for colonocytes. The GI tract microbiome of healthy individuals exhibits a predominance of gram-positive bacteria Firmicutes and Bacteroidetes and a reduced amount of Proteobacteria and Actinobacteria. This is in contrast to the microbiome of individuals with CD who have an increase in the number of the gram-negative Proteobacteria, whereas the number of Firmicutes bacteria is highly reduced. Treatment with 5‑aminosalicylic acid reduced Proteobacteria without affecting the number of other bacteria in CD‑affected individuals. Bacterial characteristics and variations in microbiome between healthy and CD‑affected individuals are summarized in Table 1. Based on the passage, to which phylum does Enterobacter most likely belong? A. Actinobacteria B. Firmiculate C. Bacteroidete D. Proteobacteria

Solution: The correct answer is D. The passage indicates that both Actinobacteria and Proteobacteria are decreased in individuals not affected by CD. By contrast, the passage specifically indicates that Proteobacteria are increased in CD-affected individuals, while there is no information regarding changes in Actinobacteria. Consequently, one cannot definitively conclude whether Enterobacter is an Actinobacterium. The passage indicates that Firmiculates decrease in CD-affected individuals, whereas Table 1 indicates that Enterobacter increase. Thus, Enterobacter cannot be a Firmiculate. The passage indicates that Bacteroidete are enriched in individuals not affected by CD, however there is no information regarding how such bacteria are altered during CD. Consequently, data in Table 1 cannot be used to determine whether Enterobacter is a Bacteroidete. The passage indicates that gram-negative Proteobacteria are increased in CD-affected individuals at the expense of Firmiculates. The table shows that Enterobacter is a gram-negative bacterium that is increased during CD, suggesting that is it a Proteobacterium.

The reaction between NADH and ubiquinone is exergonic, but the reaction, when catalyzed by Na+-NQR, does not generate much heat in vivo. What factor accounts for this difference? The reaction catalyzed by Na+-NQR in vivo: A. is more exothermic as a result of the lower activation energy. B. occurs sequentially in several small steps. C. maintains a large separation between the reacting centers. D. is coupled to the movement of a charged particle against a concentration gradient.

Solution: The correct answer is D. A. This is impossible. Even if it were true, this would make the heat generation larger, not smaller, for the catalyzed reaction. Catalysis does not change thermodynamics. B. By Hess's Law, the heat of reaction will sum and be the same. The fact that the reaction can be broken down into steps will not change the overall thermodynamics. C. This is also impossible. The reactants ultimately must be close together to react. D. The movement of a charged particle against its concentration gradient is energetically costly. Coupling the two processes: the redox reaction between NADH and ubiquinone and the movement of Na+ up a concentration gradient makes the overall process less exothermic.

In contrast to chemical messengers in classical endocrine signaling systems, chemical messengers in paracrine and autocrine signaling systems are: A. secreted by neurons only. B. not likely to bind cell receptors. C. usually transported by ducts. D. not transported by blood vessels.

Solution: The correct answer is D. Endocrine signals are released into the blood in order to impact tissues scattered throughout the body. By contrast, paracrine and autocrine chemical messengers act locally. Paracrine chemical messengers act on cells near the cell that secretes the messenger, and autocrine chemical messengers act on the same cell that secretes the messenger. Therefore, paracrine and autocrine factors do not need to be taken up in the blood to act on distant tissues.

In subsequent research, the study is expanded to examine how high-SES African American adolescents adapt to predominantly white neighborhoods. Which concept would be LEAST applicable to this follow-up study? A. Front stage self B. Intersectionality C. Social role conflict D. Demographic transition

Solution: The correct answer is D. Front stage self refers to an individual's impression management that is consistent with the expectations of a particular social role. This concept would be applicable to how an individual adapts to their social environment when they interact with others in that environment. Intersectionality (Intersectional approach) indicates that the different aspects of someone's social background (e.g., race, ethnicity, age, gender, and class) might concomitantly bestow privileges or disadvantages on an individual. The question describes the intersection of racial and class backgrounds; therefore, intersectionality would apply to the study. Social role conflict indicates the conflicting demands of two different social roles an individual carries. Role conflict would be applicable to the study if the study found that an individual experienced a role conflict between their social role associated with their family background and their role as a member of the community. Demographic transition refers to the association between the level of socioeconomic development and the balance between fertility and mortality rates in a society. Because this approach focuses on the changes at the societal level, it would be least applicable to the follow-up study which requires a micro-level approach.

The steroid progesterone has an important role in the female reproductive system. Researchers interested in studying membrane progestin receptors (MPRs) developed a method to produce and purify the protein in active form. First, the researchers devised a way to prepare a specific MPR known as hMPRα using the machinery of yeast cells. The ligand of hMPRα is derived from which compound? A. Glucose B. Phenylalanine C. Glycerol D. Cholesterol

Solution: The correct answer is D. Glucose is a simple sugar, which are not precursors to steroids. Phenylalanine is an amino acid, which are the components of proteins. Glycerol is a the trihydroxyl backbone for triacyl glycerols, which are fats. The ligand for hMPRα is the steroid progesterone. Steroids are a class of lipids that are derived from cholesterol.

In an enzyme-catalyzed reaction where enzyme concentration is held constant and substrate concentration is relatively low, which kinetic parameter will increase with the addition of more substrate? (Note: Other than substrate concentration, assume no other changes to reaction conditions.) A. KM B. kcat C. Vmax D. V0

Solution: The correct answer is D. KM, the rate constant of a reaction, does not change with changes in substrate concentration. Kcat is the reaction turnover number and does not change with changes in substrate concentration. Vmax is the maximum velocity of a reaction and is a constant property which does not change with the addition of more substrate. V0 is the initial velocity of an enzymatic reaction. At low concentrations of substrate and constant enzyme concentration, adding more substrate will increase V0 until the maximal velocity is reached.

Two theories of membrane structure are discussed below. Unit Membrane Model Phospholipid molecules are the most abundant type of lipids in cell membranes. Each consists of a nonpolar, hydrophobic tail, and a polar, hydrophilic head. The phospholipid chains orient themselves to form a bilayer with the tails pointed inward and the hydrophilic heads lined up on both sides of the bilayer. An extended monomolecular layer of protein coats both the outside of the membrane and the inside of the bilayer, but the protein does not penetrate the bilayer. When thin slices of membranes were examined with an electron microscope, three layers were seen: two electron-dense layers, with one wider layer between them. It was believed that the electron-dense layers represented proteins, and the lighter area represented lipids. Fluid Mosaic Model The structure of the fluid mosaic membrane is a bilayer of phospholipid molecules with proteins inserted into the bilayer. Hydrophilic regions of both the lipids and proteins are found on the outside surface, while the hydrophobic regions of both types of molecules are found on the inside surface. Because lipids are not fixed rigidly in the membrane, the membrane is capable of fluid movement. The theory that the proteins penetrate the lipid layer is supported when membranes are split along the middle of the lipid layer. When the top half is peeled back, small bumps can be seen on the remaining surface. These are assumed to be proteins. Question If the small bumps seen when half of the membrane is peeled away were chemically shown to consist of the lipid cholesterol, how would the Fluid Mosaic Model have to be modified? A. The proteins would have to be embedded less than halfway through the membrane. B. There could be no proteins in the membrane. C. The lipids would have to be embedded in the proteins. D. It would not necessarily have to be altered, but there would be less evidence supporting it.

Solution: The correct answer is D. Not necessarily, as transmembrane proteins could remain embedded within the membrane leaflet that was removed. Even if the small bumps were identified as cholesterol, proteins could still be positioned within the membrane leaflet that was removed. Because the middle of the bilayer is hydrophobic, the lipids do not need to be embedded in the proteins. The Fluid Mosaic Model indicates that the hydrophilic regions of proteins are found on the membrane surfaces, while the hydrophobic regions are buried among phospholipid tails. This arrangement allows proteins to span the membrane. Consistently, the passage mentions that, upon peeling back the top membrane layer, small bumps are observed. This is consistent with the idea that proteins span the membrane. If these bumps were identified as cholesterol, this does not necessarily disprove the model. Instead, it is possible that membrane-spanning proteins remain adhered to the leaflet that has been peeled back.

Although intense media coverage of the rising rates of drug dependence in the United States has increased public awareness, many individuals continue to engage in the recreational use of psychoactive drugs. The three major categories of recreational drugs are depressants, stimulants, and hallucinogens. Although these categories encompass a diverse group of chemicals with different structures, most of them increase the activity of dopamine circuits in the brain's mesolimbic system. The factors that motivate recreational drug use change as an individual gains experience with a particular drug. With continued use of alcohol and some other drugs, the user requires larger and larger doses to experience the same effect. At this point, an individual continues to use the substance in order to maintain a basic level of functionality. For instance, a chronic cigarette smoker might immediately light a cigarette upon awakening to clear a foggy head and eliminate irritability. Chronic users are also increasingly likely to experience toxicity and medical complications. Ever increasing doses of most psychoactive drugs may lead to a condition in which the person craves and uses the substance despite its adverse consequences. Given the adverse consequences of chronic drug use, research has focused on determining the factors responsible for the onset of the behavior. Novice users are typically adolescents or young adults who view drug use as a means of gaining social acceptance from a peer group. The novelty of the sensory, motor, or emotional experiences produced by the drug high is another important factor for new users. Certain personality traits, such as impulse control and sensation seeking, have been found to be associated with drug use in adolescents. In a study designed to determine whether specific traits could predict drug use, high school seniors completed a questionnaire regarding their past use of tobacco, alcohol, and illicit drugs. To assess personality, the researchers developed a brief inventory (the HP5) based on the Five-Factor Model of personality. Participants responded to 20 self-statements on a four-point response scale, where higher scores indicate that the individual has the trait being assessed. The researchers found that scores on the HP5 "antagonism" and "impulsivity" scales were the most closely associated with initial drug experimentation. Question Participants' responses to the self-statements on the inventory described in the passage could be affected by each of the following confounds EXCEPT: A. Hawthorne effect. B. demand characteristics. C. self-serving bias. D. confirmation bias.

Solution: The correct answer is D. The Hawthorne effect refers to the change in the participants' behavior when they know their behavior is being observed, including via self-report. This may affect participants' responses to the self-statements on the inventory. Demand characteristics occur if the research design provides cues to the participants regarding the study hypothesis and causes them to respond in a specific manner. This may affect participants' responses to the self-statements on the inventory. Self-serving bias refers to the tendency to attribute one's successes to internal, stable traits, and failures to situational factors. This may affect participants' responses to the self-statements on the inventory. Confirmation bias refers to the tendency to put more weight on information that confirms one's preexisting attitudes. This would not affect participants' responses to the self-statements on the inventory.

The buffers used to elute the protein contained 300 mM NaCl, 50 mM NaH2PO4 (pKa = 7.2), and various amounts of NaOH (MM = 40 g/mol). How many moles of NaCl were contained in 500 mL of the buffer solution used to elute hMPRα? A. 7.5 x 10-3 B. 3.0 x 10-3 C. 3.0 x 10-2 D. 1.5 x10-1

Solution: The correct answer is D. The concentration of NaCl in the buffer solutions was 300 mM. The amount of NaCl contained in 500 mL can be calculated as: 300 mmol/L × 500 mL × 1L/1000 mL = 150 mmol = 150 × 10-3 mol = 1.5 × 10-1 mol.

Blood flows with a speed of 30 cm/s along a horizontal tube with a cross-section diameter of 1.6 cm. What is the blood flow speed in the part of the same tube that has a diameter of 0.8 cm? A. 7.5 cm/s B. 15 cm/s C. 60 cm/s D. 120 cm/s

Solution: The correct answer is D. The flow is characterized by the continuity equation because no amount of blood is lost between the two locations. The continuity equation is 30 cm/s × π × ((1.6 cm)/2)2 = v × π × ((0.8 cm)/2)2. Solving for v yields v = 4 × 30 cm/s = 120 cm/s.

Recent studies have shown that SSRIs can also mediate their antidepressant effects by increasing brain levels of certain cytokines, including interferon gamma (IFNγ). IFNγ directly induces the expression of the protein p11 in neighboring neurons, which then interacts with 5-HTR4, a 5-HT transmembrane receptor. Figures 1 and 2 provide information about this interaction. cell stimulation with 5-HT increases cAMP levels when its cell receptor, 5-HTR4, is present According to the data presented in the passage, 5-HTR4 is a: A. protein kinase. B. tyrosine kinase receptor. C. ligand-gated ion channel. D. G protein-coupled receptor.

Solution: The correct answer is D. The passage notes that 5-HTR4 is a transmembrane protein that binds 5-HT. Figure 2 shows that cell stimulation with 5-HT increases cAMP levels when its cell receptor, 5-HTR4, is present. This suggests that 5-HTR4 is a G protein-coupled receptor because cAMP is known to be produced during G protein-coupled receptor-triggered signaling.

The migration of Vietnam-era American draft and military resisters to Canada began as a trickle in the mid-1960s and grew into a fast-flowing stream by the end of the decade. Just over 100 resisters, known more commonly as "draft dodgers" and "deserters," came to Canada in 1964. By 1965, the number was more than ten times that. Over 3,000 resisters came in 1967; from 5,000 to 8,000 came yearly through 1973. These were just the men. More women than men came, most as partners and spouses, and some on their own. This was the largest politically motivated migration from the United States since the Loyalists moved north to oppose the American Revolution. Americans formed about 20 percent of all immigrants to Canada during the period of the Vietnam War—more than any other immigrant group. Altogether more than an estimated 50,000 young Americans migrated to Canada in opposition to U.S. draft and military laws. If Americans of all ages are counted, the number is closer to 100,000. It will never be known exactly how many came or eventually stayed. Neither government kept count. By the end of the war, Senator Edward Kennedy chaired Justice Committee hearings in the U.S. Senate and instructed Justice Department officials to come forward with lists of who they were pursuing for war-related infractions. This list included 4,500 names. The American government preferred to ignore the rest. The Canadian government required no information as to why individuals came to Canada, and this enforced ignorance helped keep some hostile immigration officials honest in their treatment of war resisters seeking to enter the country. These officials were the gatekeepers to Canada, and they used interpretations of immigration law and regulations to control entry, sometimes to the disadvantage of draft resisters and, in the early stages, usually to the disadvantage of military resisters. The border was the point where resistance to American selective service and military law intersected with Canadian immigration law. This migration had serious social and political consequences for the arriving Americans as well as for Canada as a whole. Most American resisters initially came to Vancouver, Montreal, and Toronto. Many who entered elsewhere wound up in Toronto. Vancouver's labor force was tightly unionized, making jobs hard to find, and Montreal presented language problems. English-speaking and increasingly cosmopolitan Toronto became the place of settlement for the largest number of American resisters. The American resisters arrived in Canada with greater certainty about their reasons for coming than about the directions they expected their lives would take in Canada. More than three decades later, with the resisters having lived more than half of their years in Canada, it is possible to assess how the move affected their lives. Americans tend to be patriotic, and are apt to be unsympathetic to citizens who leave the country during wartime in acts of legal and political defiance against their government. Perhaps this is why neither Americans in general nor American social scientists in particular have given much attention to the exiles of the Vietnam generation. Also, like much else that happens outside of America's borders, exiles tend to be ignored and forgotten. Those both inside and outside the war resistance movement often saw the American war exiles as either making a self-serving "end run" around American law or withdrawing from the war resistance by going to Canada. To those in the U.S., the exiles remain a largely unknown and marginalized group. Yet exile was the end neither of the expatriates' life stories nor of their significance. Question For which of the following assertions does the author provide an explanation in the passage? A. "More women than men came..." B. "The American government preferred to ignore the rest." C. "This migration had serious social and political consequences..." D. "Many [resisters] who entered elsewhere wound up in Toronto"

Solution: The correct answer is D. While the author implies a reason why some women migrated (to be with partners), there is no explanation as to why more women than men migrated-only that "most [women migrated] as partners and spouses, and some on their own" (first paragraph). Explanation is not provided for the wide discrepancy between the estimated numbers of resisters who migrated to Canada and the much smaller number of those the American government "pursu[ed] for war-related infractions" (paragraph 2). "The American government preferred to ignore the rest" (paragraph 2) refers to this wide discrepancy, but there is no explanation as to why the American government did not pursue "the rest" (i.e., most of the migrants). Paragraph 3 ends with this statement that "This migration had serious social and political consequences for the arriving Americans as well as for Canada as a whole." Explanation of these social and political consequences is not provided and the next paragraph shifts to a different topic (the cities in Canada to which the migrants primarily moved). The author gives several reasons as to why many of the resisters/migrants eventually moved to Toronto: "Vancouver's labor force was tightly unionized, making jobs hard to find, and Montreal presented language problems. English-speaking and increasingly cosmopolitan Toronto became the place of settlement for the largest number of American resisters" (paragraph 4).

Look on back Solution: The correct answer is D. None of the bacteria analyzed produce glucose. Of the bacteria assessed, only Enterobacter produces lactate. Since Enterobacter is increased in CD-affected individuals, lactate production most likely increases, not decreases. Enterobacter is the only LPS producer assessed and Enterobacter is increased during CD. Thus, LPS production is increased, not decreased, in CD-affected individuals. Three of the producers of butyrate (Roseburia, Odoribacter, and Faecalibacteria) are reduced in CD-affected individuals.

The GI tract microbiome of healthy individuals exhibits a predominance of gram-positive bacteria Firmicutes and Bacteroidetes and a reduced amount of Proteobacteria and Actinobacteria. This is in contrast to the microbiome of individuals with CD who have an increase in the number of the gram-negative Proteobacteria, whereas the number of Firmicutes bacteria is highly reduced. Treatment with 5‑aminosalicylic acid reduced Proteobacteria without affecting the number of other bacteria in CD‑affected individuals. Bacterial characteristics and variations in microbiome between healthy and CD‑affected individuals are summarized in Table 1. Which product is particularly reduced in CD-affected individuals? A. Glucose B. Lactate C. LPS D. Butyrate

Look on back Solution: The correct answer is D. There is no information indicating that any of the bacteria listed in Table 1 impact polypeptide digestion. Dietary fibers are not absorbed by the human intestine. Based on Table 1, the two bacteria that produce propionate, Phascolactobacteria and Odoribacter, are decreased in CD-affected individuals. Thus, the levels of propionate are most likely decreased, rather than increased, in CD-affected individuals. As explained in the passage, molecules such as butyrate, acetate, and propionate inhibit the inflammatory response against commensal bacteria of the GI tract. CD is an inflammatory condition, in which Table 1 indicates that many bacteria producing these anti-inflammatory molecules are reduced during CD. This is consistent with the interpretation that inflammation observed during CD is caused by decreased production of propionate, butyrate, and acetate, which decreases immune tolerance of commensal bacteria.

The microbiome has been investigated for its possible link to non-hereditary diseases. Crohn's disease (CD) is a non-hereditary chronic inflammatory condition that may affect any part of the gastrointestinal (GI) tract. Causes for CD have not been defined to date; however, research has shown that the profile of the GI tract microbiome is different in healthy versus CD‑affected individuals. Therefore, researchers hypothesized that differences in bacterial distribution and the host immune response to GI tract bacteria might play a role in the establishment and progression of the disease. GI tract bacteria digest dietary fibers and convert them into butyrate, propionate, and acetate. These three molecules modulate the innate immune system response by attenuating the inflammatory response to GI tract commensal bacteria. Furthermore, butyrate is a major source of energy for colonocytes. The GI tract microbiome of healthy individuals exhibits a predominance of gram-positive bacteria Firmicutes and Bacteroidetes and a reduced amount of Proteobacteria and Actinobacteria. This is in contrast to the microbiome of individuals with CD who have an increase in the number of the gram-negative Proteobacteria, whereas the number of Firmicutes bacteria is highly reduced. Treatment with 5‑aminosalicylic acid reduced Proteobacteria without affecting the number of other bacteria in CD‑affected individuals. Bacterial characteristics and variations in microbiome between healthy and CD‑affected individuals are summarized in Table 1. Based on the passage, the microbiome of CD-affected individuals will result in which physiological change? A. Increased polypeptide digestion B. Slower dietary fiber absorption C. Increased amount of propionate D. Decreased immune tolerance

Look on back Solution: The correct answer is B. The information in the passage indicates that exercise correlates with increased FNDC5 expression. Additionally, mice overexpressing FNDC5 exhibit lower nonfasting glucose levels, most likely because of higher, not lower, cellular glucose uptake. According to the pathway suggested by the information in the passage, exercise ultimately increases UCP1 levels which in turn degrades the proton gradient that drives oxidative phosphorylation. More energy is dissipated as heat and less is used to synthesize ATP. The passage notes that irisin is secreted into blood and therefore it would be an endocrine, not an exocrine, secretion of skeletal muscle. The passage notes that irisin is a protein formed by cleaving the extracellular domain of FNDC5 which is expressed in skeletal muscles, not adipose tissues.

The number of calories used during physical exercise is greater than the number of calories used for the movements themselves. This may be caused in part by exercise-induced expression of uncoupling protein 1 (UCP1) in subcutaneous fat. Subcutaneous fat is mostly white fat cells but can also contain brown fat cells in mice and humans. As part of a thermogenesis program, UCP1 directly reduces the proton gradient driving oxidative phosphorylation. UCP1 expression is a characteristic of brown fat cells only and is induced by the protein irisin. The data in Table 1 address the relationship between exercise and: expression of UCP1 in subcutaneous fat cells, expression of FNDC5 (a transmembrane protein in skeletal muscle plasma membranes), blood levels of irisin (a soluble protein formed by cleaving the extracellular domain of FNDC5), and expression of adiponectin (a hormone produced by white fat cells) in both wild-type mice and mice with overexpression of skeletal muscle PGC-1α (a transcription factor whose expression in skeletal muscle is induced by exercise). The information in the passage best supports which hypothesis? A. Exercise prevents glucose uptake. B. Exercise promotes less effective cellular respiration. C. Exocrine secretions of skeletal muscle act on adipose tissue. D. Endocrine secretions of adipose tissue act on skeletal muscle.

Look at definition side for the question Solution: The correct answer is D. A. This is 1/4 of the actual pressure. Pressure is the ratio of the force applied perpendicular to a surface and the area of the surface. Because the normal component of the force is 100 N and the area is 10 cm × 5 cm = 50 cm2 = 0.005 m2, the pressure is (100 N)/(0.005 m2)=20 kPa. B. This is 1/2 of the actual pressure. Pressure is the ratio of the force applied perpendicular to a surface and the area of the surface. Because the normal component of the force is 100 N and the area is 10 cm × 5 cm = 50 cm2 = 0.005 m2, the pressure is (100 N)/(0.005 m2) = 20 kPa. C. This is 3/4 of the actual pressure. Pressure is the ratio of the force applied perpendicular to a surface and the area of the surface. Because the normal component of the force is 100 N and the area is 10 cm × 5 cm = 50 cm2 = 0.005 m2, the pressure is (100 N)/(0.005 m2) = 20 kPa. D. Pressure is the ratio of the force applied perpendicular to a surface and the area of the surface. Because the normal component of the force is 100 N and the area is 10 cm × 5 cm = 50 cm2 = 0.005 m2, the pressure is (100 N)/(0.005 m2) = 20 kPa.

The principal component of a defibrillator is a capacitor. It is charged by placing the switch in Position C in Figure 1. Figure 1 Schematic of a defibrillator The capacitor consists of a pair of metal plates separated by a dielectric. During defibrillation the switch is placed in Position D, discharging the capacitor through paddles pressed against the chest of the patient. Firm force (~100 N) and a conductive gel pad are used to improve the electrical contact between each paddle and the patient's chest. Based on the passage, which of the following is closest to the pressure exerted on the chest by a 10 × 5 cm rectangular paddle during defibrillation? (Note: 1 Pa = 1 N/m2.) A. 5 kPa B. 10 kPa C. 15 kPa D. 20 kPa

Biases can influence how we process new information and update our beliefs. In Study 1, researchers examined the conditions under which individuals are willing to update their beliefs about the frequency of various negative life events, such as Alzheimer's disease or robbery. In the first phase of the experiment, the participants were asked about their preconceived notions of the frequency of negative events. The researchers found a tendency to underestimate the frequency of negative events. The participants also believed that they were at a lower risk of experiencing negative events compared to other individuals. In the second phase of the experiment, the participants were given new information about the frequency of various negative events. Sometimes the new information was better than what the participant expected (for example, they were told that negative events occur less frequently than they had thought). Other times, the new information was worse than expected. The results showed that people were more likely to update their beliefs when the new information suggested that negative events were less likely than they expected. In Study 2, another group of participants watched a short clip depicting a car accident. A week later, the participants were presented with a written summary of the clip they viewed previously. For Group A, the written summary contained small errors that made the car accident in the video appear more serious than it really was. For Group B, the written summary contained small errors that made the car accident appear less serious than it really was. For the control group, the written summary contained no errors. After a delay of one more week, the participants were asked to retrieve their memory of the original video as accurately as they could. The researchers were interested in the participants' likelihood of creating false memories for the car accident. Based on the findings from Study 1, will Group A have a higher incidence of constructing false memories than the control? Will Group B have a higher or lower incidence of constructing false memories compared to Group B?

higher; higher

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