Skip to main content
Sign in Create a free account
Varsity Tutors
Sign in Sign up

Practice Test 12 - MCAT Biological and Biochemical Foundations of Living Systems

20 questions. Answer them in any order, then submit to see your score and every explanation.

  1. During rational design, an enzyme pocket is made more hydrophobic to favor binding of a nonpolar drug-like ligand. Which residue side chain is most consistent with increasing local hydrophobicity without adding charge at pH 7.4?
  2. A pharmacologic agent prevents vesicle acidification but does not block vesicle formation or fusion. A receptor that normally releases its ligand in endosomes and recycles to the plasma membrane instead remains ligand-bound and is increasingly routed to lysosomes. Which prediction is most consistent with this change?
  3. A membrane channel is a trimer, and each subunit contributes one transmembrane αα-helix to form a central pore. A mutation introduces a proline in the middle of the transmembrane helix of one subunit; the channel still assembles as a trimer but shows reduced ion conductance. Based on secondary structure, what is the most likely consequence of the proline substitution?
  4. A human prenatal karyotype reveals 47,XX,+21. The parents have normal karyotypes. The mother is 40 years old. Which meiotic event is most consistent with the chromosomal finding in the fetus?
  5. In a study of spermatogenesis, researchers briefly exposed primary spermatocytes (2n) to a reversible microtubule inhibitor during meiosis I, then washed it out before meiosis II. They later isolated individual sperm and genotyped two genes located on different chromosomes. Compared with untreated cells, which outcome would be expected from the described meiotic event?
  6. A venous blood sample is analyzed before and after passage through the lungs. Without invoking disease, which transformation most directly accounts for the large increase in oxygen content across the pulmonary circulation?
  7. A cell line is engineered to constitutively express high levels of cyclin B throughout interphase. Despite this, most cells do not enter mitosis prematurely unless CDK1 inhibitory phosphorylation is also reduced. Which regulatory principle is best illustrated by this finding?
  8. A research group compared two differentiated cell types derived from the same donor: hepatocyte-like cells and neuron-like cells. Both expressed similar levels of a housekeeping gene. However, only neuron-like cells expressed high levels of a neuron-specific gene (Gene N). ChIP-qPCR showed strong enrichment of a repressive histone mark at the Gene N promoter in hepatocyte-like cells but not in neuron-like cells. Cellular principle assessed: histone modifications regulating lineage-specific gene expression. Which outcome would be expected if the repressive mark at the Gene N promoter were experimentally removed in hepatocyte-like cells?
  9. A laboratory colony of mice was established from a single pair heterozygous at many loci. Over multiple generations, investigators compared genetic diversity in offspring produced by (i) normal germline meiosis and (ii) clonal expansion of a single embryonic stem cell line followed by nuclear transfer to generate genetically matched animals. Whole-genome SNP analysis showed substantially higher within-litter genotype diversity in the meiosis-derived offspring than among animals derived from the stem-cell nuclear transfer protocol. Which feature of meiosis is most consistent with the increased within-litter diversity observed in the normal breeding group?
  10. A researcher compares growth of a facultative anaerobe at 37°C in identical medium containing 20 mM glucose, but with either vigorous aeration or an anoxic chamber (no O2). pH is maintained at 7.0. OD600 is measured after 4 hours. Table (OD600 at 4 h): Aerobic: 0.95 Anoxic: 0.45 Which conclusion is most supported by the experimental results?
  11. A patient with severe dehydration from gastroenteritis is placed in a warm room. Clinicians note reduced sweating compared with baseline, and skin temperature rises despite intact mental status. The thermoregulatory principle is sweat production supporting evaporative cooling. Which outcome is most consistent with thermoregulation under reduced body water availability?
  12. An epithelial sheet separates two chambers. The apical side contains 100 mM NaCl; the basolateral side contains 100 mM NaCl. A non-permeant solute (mannitol) is added to the apical side only, increasing apical osmolality by 100 mOsm/kg. The epithelium has high water permeability and low mannitol permeability. Principle tested: effective osmotic gradients (tonicity) drive water movement when solute cannot cross. Which outcome is most consistent with the process described?
  13. A research vignette describes a chick embryo during gastrulation: cells that move inward and replace the hypoblast form a continuous epithelial sheet that later becomes the lining of the digestive tract. The investigators emphasize that this layer is internal, forms a tube, and is specialized for absorption and secretion. Which structure is most likely derived from this layer?
  14. Researchers express a secreted cytokine in cultured mammalian cells. The wild-type cytokine is efficiently detected in the culture medium. A mutant cytokine lacking its N-terminal hydrophobic signal peptide is synthesized at similar levels (cell lysate immunoblot) but is not detected in the medium. Which process is most likely involved in the normal secretion of the wild-type cytokine? (Assume the mutant protein remains soluble and is not rapidly degraded.)
  15. In a cell-based assay, ligand L activated a GPCR and increased cAMP. After prolonged exposure to L, the cAMP response to a second L dose was diminished, but the response to a direct adenylyl cyclase activator was preserved. Which outcome would be expected if the receptor is blocked during the first L exposure?
  16. Investigators studied acute dehydration in healthy adults after 12 hours without fluid intake. Participants then received an IV infusion of hypertonic saline (3% NaCl) for 30 minutes while blood pressure was maintained within normal range (mean arterial pressure change <5 mmHg). Plasma osmolality increased from 290 to 305 mOsm/kg, and plasma Na+ increased from 140 to 148 mM. Despite stable renal perfusion pressure, urine volume fell over the next hour and urine osmolality rose. Which renal response would you expect given this scenario as the primary mechanism maintaining homeostasis of plasma osmolality?
  17. A study of antigen presentation compared two peptides of identical sequence but different backbone modifications: peptide X contains all standard peptide bonds; peptide Y contains one N-methylated amide bond. In a proteasome digestion assay, peptide Y was less efficiently cleaved near the modified position. Which statement best explains this result in terms of peptide bond chemistry and primary structure processing? (Assume the proteasome recognizes backbone features during catalysis.)
  18. In an experiment on calcium signaling, researchers inhibit the sarcoplasmic/endoplasmic reticulum Ca2+^{2+}-ATPase (SERCA), a pump that moves Ca2+^{2+} from the cytosol into the ER lumen. The ER is a membrane-bound organelle that stores Ca2+^{2+} and supports folding of secreted proteins. After SERCA inhibition, cytosolic Ca2+^{2+} rises transiently, then cells show increased markers of ER stress and reduced secretion of a reporter protein. What cellular change is most consistent with impaired ER Ca2+^{2+} homeostasis?
  19. A lab compared synaptic delays between two neuron pairs. Pair 1 showed a consistent delay of ~0.5 ms between presynaptic spike and postsynaptic response; Pair 2 showed a delay of ~2.0 ms and occasional failures. The concept being tested is the distinction between electrical and chemical synapses in signal transmission. Which interpretation is most consistent with these findings?
  20. Two ligands, X and Y, were tested on the same cell type. X causes receptor autophosphorylation on tyrosine residues and recruitment of adaptor proteins, followed by increased ERK phosphorylation. Y causes a rapid increase in cAMP without detectable receptor phosphorylation. Both ligands increase cell proliferation after 24 hours. Which cellular response is most consistent with the signal transduction pathway described for ligand X (but not Y)?

Practice tests