mcat science 9

  1. Klinefelter syndrome is thought to derive from a nondisjunction event during either paternal or maternal meiosis I. If the event occurs during oogenesis, what is the expected ploidy of the four resulting gametes, prior to fertilization? 

    n + 1, n + 1, n – 1, and n – 1 

    We must know for test day that Klinefelter is a sex chromosome trisomy where a male embryo receives and extra X chromosome, becoming 47XXY. Diploid cells are the normal product of meiosis I.

    Failure of homologous sex chromosomes to separate properly in meiosis I would, at the conclusion of meiosis II, produce two gametes with an extra sex chromosome and two that are missing a sex chromosome.
  2. ______ is the process by which long chain hydrocarbons are oxidized to acetyl-CoA by enzymes in the mitochondria.
    Beta oxidation
  3. an important effect of glucocorticoids such as cortisol is immunosuppression.
  4. Besides desmosomes, which other cell structures connect cells? 


    I. Hemidesmosome

    II. Tight junctions

    III. Gap junctions
    II and III only 

    Tight junctions connect cells in a waterproof manner, and gap junctions connect cells in a way that allows the cytoplasm of one cell to be continuous with the cytoplasm of another.

     Hemi-desmosomes connect a cell to the extracellular matrix, and therefore do not provide cell-cell connections
  5. N-C

    5`- 3`

    Extracellular space - cytoplasm
  6. keratin = intermediate filament

    actin - microfilament
  7. These are the cells that produce the fibers comprising connective tissues such as collagen. So they synthesize collagen
  8. the basement membrane connects to epithelial layer and endothelial capillaries through
  9. Cadherins form cell-cell junctions, not junctions between the cell and the extracellular matrix.

     Occludin comprises tight cell-cell junctions.
  10. Which of the structures below is NOT an exocrine gland? 

    A. The liver 

    B. The pancreas 

    C. A gastric chief cell 

    D. The adrenal gland
    D (adrenal gland) is correct. Of the options listed, only D has no exocrine function. The liver and pancreas secrete many hormones into the bloodstream, but also release digestive enzymes into the lumen of GI tract, an exocrine function. Gastric chief cells are purely exocrine and secrete pepsinogen into the stomach.

    • ex·o·crine:
    • relating to or denoting glands that secrete their products through ducts opening onto an epithelium rather than directly into the bloodstream.

    im gassy cuz of pepsi

    gastric chief cells --> pepsinogen
  11. Cloudin and occludin are the proteins that form tight junctions between epithelial cells. Therefore, any organ that relies on tight junctions will be negatively affected if their synthesis is impaired. If the intestinal lining is to properly absorb nutrients while leaving behind undesired materials, free diffusion cannot be permitted between the digestive ECM and the lumen of the digestive tract. Tight junctions seal the gaps between epithelial cells in the intestine, allowing cells to selectively control what passes through the epithelium through the use of transmembrane transport proteins. Without tight junctions, nutrient concentrations would equalize due to diffusion through the epithelium, vastly decreasing the efficiency of the GI tract.

    so defect in synthesis of occludin and cloudin would impair intestinal lining
  12. Sensory, or afferent, tracts lie toward the rear (dorsal) side of the spinal cord. In contrast, motor, or efferent, tracts are positioned near the front (ventral) and lateral sides. If only the ventral nerves are severed, the worker should retain sensation in body parts below the injury, but will likely suffer problems with the mobility of both voluntary and involuntary muscles.
  13. what color matter?

    myelinated vs unmyeliminated
    myelinated = white matter

    unmyelinated = gray matter
  14. ______ cells perform maintenance in the brain, (immune)

    while ______ help support the blood-brain barrier.

  15. ______ neurons like #3 predominate in the CNS and the cerebrum specifically; their many dendrites allow them to integrate into a complex neural network capable of complicated responses.

    _____ neuron. Such simple neuron structures are rare in humans, though common in some insects.

    ______ neuron; these cells are common in special sensory organs, and are most commonly remembered as components of the retina.

    ______ neurons like #4 typically transmit sensory information from the periphery to the central nervous system.



  16. Myelination has no effect on neuron excitability. It only affects conduction velocity.

    so it would be more likely a neuron fires an action potential if multiple EPSP summate temporally than a single EPSP regardless of which is myelinated
  17. During most of the duration of an action potential, another stimulus, regardless of its strength, cannot cause the neuron to fire again. This is termed the absolute refractory period, and it can be attributed to: 

    A. the fact that sodium channels are closed. 

    B. the fact that sodium channels are inactivated.
    B. the fact that sodium channels are inactivated.
  18. action potential occurs at
  19. At +35mV, voltage-gated sodium channels inactivates QUICKLY while voltage-gated potassium channel SLOWLY opens and the deflux of K+ ions start to leave the cell.
  20. Oxytocin, like ADH, is produced in the hypothalamus, then stored in and secreted by the posterior pituitary.

     Remember that the posterior pituitary does not produce or synthesize the hormones it secretes! ADH is produced in the hypothalamus, then stored and released from the posterior pituitary.

    TSH is produced and secreted from the anterior pituitary.
  21. subcutaneous layer also known as

    The name given in the question stem provides a major hint. Remember, the prefix “sub” means “below,” so we are looking for a lower, or more interior, layer of the skin. The hypodermis is the most interior layer and consists mostly of fat deposits.
  22. The human epidermis can be described as a stratified squamous epithelium. The term “stratified” denotes the multi-layered nature of this tissue, which is vital for protective purposes.
  23. _______ connect bones to other bones, while ______ attach bone to muscle.

  24. Irregular bones, as their name implies, are those that do not fit the classification for either short, long, or flat bones. Examples include the vertebrae and mandible.

     The femur is a long bone, not an irregular bone.

     The sternum is an example of a flat bone.

     The metatarsals, which are small bones in the foot, exemplify short bones.
  25. When action potentials occur at a high frequency within motor neurons, their effects accumulate in a process termed wave summation. Here, the muscle does not have enough time between stimulations to fully relax; this ramps up motor unit recruitment and total exerted force until tetanus is reached.
  26. For skeletal muscle to relax, the conformation of myosin must change as ATP binds the myosin head, decreasing its affinity for actin, and breaking the cross-bridge between thick and thin filaments. Additionally, the free Ca2+ concentration in the sarcomere itself must go down, returning tropomyosin and troponin to their resting positions. This requires use of the Ca2+ ATPase in the sarcoplasmic reticulum.

    thin = actin
    thick = myosin
  27. Upon downregulation of acetylcholinesterase, the concentration of acetylcholine will increase. Remember, in the parasympathetic nervous system, acetylcholine lowers heart rate and blood pressure by acting upon muscarinic channels in cardiac muscle. However, ACh also causes muscle contraction at the neuromuscular junction.
  28. The Z line is the name given to the junction, or “border,” at either end of the sarcomere. These structures are orthogonal to the direction of contraction and do not expand or become smaller during muscle movement.

    A: The H zone, which refers to the unoverlapping area between thin filaments in the center of the sarcomere, does decrease in size upon contraction. Remember, the thin and thick filaments do not contract themselves, but instead slide relative to one another. For this reason, the area of both thin and thick filaments that do not overlap must shorten.

    C: The I band also shortens during contraction. This term describes the area between the ends of the myosin thick filaments and the Z line.
  29. Slow oxidative fibers, in addition to the characteristics mentioned in the question stem, are slow to contract. These fibers have a high concentration of myoglobin to supply the oxygen needed for aerobic respiration.

    A: Fast glycolytic fibers are low in myoglobin and whitish in appearance. As their name suggests, these cells depend heavily on anaerobic respiration; for this reason, they require relatively little oxygen.

    B: Fast oxidative fibers do contain abundant myoglobin. However, they contract very rapidly and, while resistant to fatigue, are less so than slow oxidative fibers.
  30. Oxytocin perpetuates labor by increasing uterine elasticity, which leads to stimulation of uterine stretch receptors. These positively feed back to the pituitary to increase oxytocin production. However, increasing uterine elasticity has no effect if the uterus is not already in the process of contracting. Interestingly, the initial signal for the induction of labor is still unknown.

    II: The oxytocin circuit during parturition is a positive feedback loop. Exogenous oxytocin leads to further release of oxytocin.

    what kind of hormone oxytocin peptide or steroid?
  31. hCG is required to permit embryonic implantation and continued embryonic growth. If hCG levels are too low, the embryo is attacked by maternal lymphocytes at the site of attachment and ultimately expelled from the uterus.
  32. When the oocyte is released from the follicle, it is surrounded by a layer of maternal follicular cells known as the cumulus oophorus. Which of the choices below is a plausible function of the cumulus oophorus? 

    It produces vital amino acids and other molecules to support the fragile oocyte. This is the true function of the cumulus oophorus. Since metabolic processes generate free radicals and other toxic byproducts, the oocyte must remain as metabolically inactive as possible to protect its haploid genome. The cells described conduct most necessary metabolic processes and export the products to the oocyte.
  33. The glomerulus is a bundle of capillaries adjacent to the Bowman’s capsule, or entrance to the nephron. It begins the process of urine formation by pushing (or filtering) blood into the Bowman’s capsule. Both platelets and red blood cells are too large to exit the glomerulus and are prevented from entering the filtrate.

    II: Sodium is a major component of the filtrate and certainly exists within the nephron.

    III: Glucose is small enough to enter the filtrate; it is just quickly reabsorbed in healthy individuals.
  34. The loop of Henle functions to:

    form a solute gradient in the medulla of the kidney, allowing for the later movement of water through channels in the collecting duct.

    The loop of Henle is likely one of the most confusing aspects of MCAT-level human physiology. While many students think that the loop actually concentrates urine itself, it simply prepares the medulla of the kidney for the later absorption of water. Specifically, the antiparallel nature of the loop establishes a countercurrent multiplier system that makes the inner medulla very solute-rich. Interestingly, the collecting duct also runs parallel to this long structure. When ADH is present, as in periods of dehydration, the collecting duct is made water-permeable through the introduction of aquaporin channels. Since the medulla is now so salty, water can passively exit the nephron and remain in the body.
  35. proximal convoluted tubule

    Simple cuboidal epithelia are well-suited for solute transport and absorption. In addition, the presence of microvilli should remind you of the small intestine, where nutrient absorption is a main function. Of the choices given, the only region of the nephron that is heavily involved in absorption is the PCT. Cells lining this structure must reabsorb glucose, sodium, amino acids, and other vital solutes while also permitting the secretion of ions and toxins.
  36. Filtration refers to the original movement of fluid and solute (platlets and RBC) into the Bowman’s capsule from glomerulus

    , while secretion relates to the transport of specific toxins and protons into later regions of the nephron.
  37. G cells, release gastrin. Additionally, gastrin promotes the secretion of hydrochloric acid.

    pepsinogen is produced by chief cells in the stomach, then stimulated by the low pH to be cleaved into pepsin.

    Pepsinogen is a zymogen, or inactive enzyme precursor, that is released by chief cells. This prevents pepsin, a protease, from degrading stomach cells while it is stored. Once released into the stomach, the low pH denatures the pepsinogen protein and reveals cleavage points that neighboring pepsinogen molecules attack to produce pepsin.

     Bicarbonate is produced by the pancreas
  38. zymogens

    Trypsin is formed in the small intestine when its proenzyme form, the trypsinogen produced by the pancreas, is activated. Trypsin cleaves peptide chains mainly at the carboxyl side of the amino acids lysine or arginine

    chymotrypsin selectively cleaves peptide bonds formed by aromatic residues (tyrosine, phenylalanine, and tryptophan) prefers to cleave next to bulky, hydrophobic amino acids (its zymogen precoursor is chymotrypsinogen)

    Pepsinogen is a zymogen, or inactive enzyme precursor, that is released by chief cells. This prevents pepsin, a protease, from degrading stomach cells while it is stored. Once released into the stomach, the low pH denatures the pepsinogen protein and reveals cleavage points that neighboring pepsinogen molecules attack to produce pepsin.
  39. hydrolysis of an ester, a reaction that is sometimes known as saponification. In humans, this process is catalyzed by pancreatic lipase. Fatty acids, which are produced along with glycerol, are assembled into small spheres known as micelles in the lumen of the small intestine. Finally, these micelles are converted to chylomicrons inside intestinal cells.
  40. ____ attach epidermal cells to demal cells or epithelial cells to basement membranes or underlying structures
  41. which bonds are easier to break and harder to break when denaturing a protein and causing it to lose 3` structure 

    acid base
    h bonds
    covalent bonds
    peptide bonds
    hydrophobic bonds
    hard to break - covalent and peptide

    easier - h bonds, hydrophobic, and acid base
  42. failure of cell division as a result of multiple molecular and metabolic processes

    ___ is ability of one group of cells to influence to fate of other nearby cells

  43. a capillary has:

    higher hydrostatic pressure at arteriole end and lower hydrostatic pressure at venule end

    - higher osmotic pressure in blood plasma than interstitial fluid

    - hydrostatic pressure results from beating of heart
  44. exothermic = increase temp shift ___

    endothermic = increase temp = shift ___

    increase pressure goes to ____ moles gas

    Carbonation refers to reactions of carbon dioxide to give carbonates, bicarbonates, and carbonic acid.


  45. diploid number is 24 then number of chromosomes in each egg cell is
  46. polysaccharides from exclusively from glucose monomers:

    what type of linkage?


    glycogen mostly has alpha 1-4 but some alpha 1-6
    • cellulose: beta 1-4
    • amylose: alpha 1-4
    • amylopectin: alpha 1-4 and alpha 1-6

    glycogen mostly has alpha 1-4 but some alpha 1-6
  47. SN2 reactions favor different nucleophiles using different polar protic and polar aprotic solvents, using a nonpolar solvent would make it so that reactants cant mix well together and would halt enzymatic activity and denature proteins
  48. adjacent DNA basepairs experience stabilized stacking interactions which are ______
    van der waal non-covalent interactions
  49. respiratory alkalosis - decreased CO2

    metabolic alkalosis - increased HCO3-
  50. Ksp won't change if temperature doesn't change.

    add sodium urate crystal to NACl AND molar solubility decrease
  51. for endothermic, increasing temp (shift right) cause keq to increase or decrease?
  52. ribosomes are made in the ____

    cell membrane

    are made in sER
    nucleolus (part of nucleus)
  53. 10:1 vs 10:0

    beta oxidation between the two is the saturated fatty acid would produce two more ATP as FAD+ being reduced to FADH2 is already done in unsaturated so difference is between 1 FADH2
  54. tautomers are what kind of isomers?
    constitutional because they differ in placement of H atom and double bond
  55. pyruvate decarboxylation: pyruvate dehydrogenase to form acetyl Coa (for CAC)

    pyruvate decarboxylase converts pyruvate to acetaldehyde in anaerobic fermentation
  56. estrogen in mestrual cycle:

    in follicular phase it negatively feedbacks to hypo and anter pit to inhibit release of GnRH , FSH, and LH but at end of follicular phase it positive feedbacks to hypothalamus and anterior pitutary to trigger ovulation 

    A spike in LH and FSH (“LH surge”) causes ovulation, following a suppression of GnRH. Estrogen levels continue to rise following ovulation and the corpus luteum forms, which secretes progesterone in significant levels and causes decreases in LH and FSH levels.

    -estrogen peaks b4 day 14
    -LH/FSH peak at day 14
    -Progesterone peak after day 14
  57. insulin release has appetite supression effect

    acute stress = appetite supression to focus on more immediate dangers

    chronic stress = appetite increase
  58. buffer use weak acid or base and its conjugate salt

    so strong acids (HCl) and bases can't be used
  59. H2C2O4 = 90 MW

    Normality = 2

    gram equivalent = 45
  60. NaBH4 reduces aldehydes and ketones to alcohols / diols, not H2O2
  61. nipple suckling stimulates hypothalamus to synthesize oxytocin to be released by posterior pituitary so smooth muscle in breast contract to release milk 

    also hypothalamus stops releasing dopamine onto anterior pituitary so prolactin can be secreted by anterior pituitary
  62. in order to reduce lactic acid production glucose intake should be limited so a diet in purely ketogentic amino acids (lysine / leucine) is used
  63. growth hormone raises blood glucose by:

    - stimulate lipolysis
    - gluconeogensis
    - inhibit glycogenesis
  64. chalcogens - group 16 to the left of halogens
  65. thin layer chromatography is best to separate amino acids based off polarity like between tyrosine, tyrptophan, histidine, glycine
  66. mean to the right of median = skewed right

    median lower than mean
  67. gel electrophoresis can separate molecules based off charge and size

    *** southern blot probes for specific DNA sequences AFTER they have been separated.
  68. _____ activates trypsinogen to trypsin, procarboxypeptidase A and B to carboxypeptidase A and B and trypsin activates chymotrypsinogen to trypsinogen
  69. cholecycstokinin is a _____ hormone that stimulates digestion of _____ and ______

    fats  and proteins
  70. proofreading occurs in BOTH prokaryotes and eukaryotes but is more effective in eukaryotes and it occurs during S phase
  71. Boron is a metalloid that can act as a lewis acid (metal) or anion (non metal)
  72. keq = 1     same as    deltaG = 0

    keq > Q or keq > 1 =spontaneous
  73. when is the first meiotic division of oogenesis completed forming the secondary oocyte?
    shortly before ovulation
  74. malate dehydrogenase makes oxaloacetate and does not lead to loss of CO2 or carbon
  75. in dehydration urine will be created that is hypertonic to blood

    in overhydration urine will be created that is hypotonic to blood
  76. ketone + alcohol =

    aldehyde + alcohol =

  77. hair follicles , sweat glands , blood vessels originate from the ______
  78. ketones enter CAC as acetyl CoA and therefore cannot be used by RBCs cuz they lack _____
  79. alpha vs beta linkage

    • maltose - alpha
    • sucrose - alpha
    • cellulose - beta
    • lactose - beta
    • starch - alpha
  80. IR better at identifying precise molecules than UV

    UV light has more energy than IR, and better at determining extent of conjugation
  81. aldol condensation:

    base is needed to remove hydrogen from ketone or aldehyde forming an ______ which can then be used to nucleophilic attack the electrophillic carbon on carbonyl group
  82. hydrogen bonds are an unusually strong form of dipole dipole interaction
  83. ________ have two alcohol groups on the same carbon. When made from reactions involving carbonyl groups nucleophillic oxygen (usually made from water) will attack electrophillic carbonyl carbon.

    They do not have to be on terminal carbon.
    geminal diols
  84. _________ reactions involve BOTH oxidation and reduction.
  85. KMnO4 and (CrO3, H2SO4) can oxidize primary alcohols to _______ .

    PCC oxidize primary alcohols to _____ .
    carboxylic acids cuz they strong oxidizing agents.

  86. cDNA libraries feature only coding regions of DNA while genomic libraries include both coding and noncoding regions.

    cDNA - Generated by reverse transcribing mRNA.

    Genomic DNA library - generated from cloned DNA fragments that have been digested by restriction enzymes.

    Since cDNA library represent reflect genes after their mRNA transcripts have undergone post-transcriptional processing they can more reliably be used to synthesize recombinant proteins
  87. Once egg fertilized - secretes hCG in small amounts.

    After implantation - Placenta secretes hCG in large amounts to maintain corpus luteum in 1st trimester.

    Corpus luteum - produce progesterone during first trimester and menstrual cycle.

    Ovaries - Produce estrogen.
  88. Ovulation is indicated by ______
    a surge in LH and FSH
  89. fastest rate for SN1 is one that is most stable carbocation formed.
  90. DNA Pol gamma replicates mitochondrial DNA only in eukaryotes 

    single strand binding proteins stabilize unwound template strands in both euk and prokaryotes

    which one utilizes only one origin or replication and which utilizes multiple between eukaryotes and prokaryotes?
    eukaryotes - multiple

    prokaryotes - one
  91. phosphatidylcholine:

    2 fatty acids , 1 glycerol , 1 phosphate , 1 choline
  92. 3 oxopentanoic acid + heat =
    3 oxopentanoic acid + heat = butanone
  93. In a daniell cell once salt bridge becomes depleted the cell will stop running due to increasing counter-voltage
  94. double the amount of enzyme will affect _____ but not affect ______

    km - it is independent of concentration
  95. LiAlH4 will reduce carbonyls to alcohols
  96. starvation 

    since body would rather use lipids as food source because proteins aren't meant to be used that way the body makes ketone bodies from lipids
  97. which has greater affinity for oxygen, maternal or fetal hemoglobin?

    which side of heart has higher pressure in adults and in fetus?

    in fetus umbilical arteries carry deoxygenated blood towards placenta and umbilical veins carry oxygenated blood away from placenta

    • right - fetus
    • left - adult
  98. 1 Pa . L = 1  J

    P = Change in energy / change in time
  99. ATP Hydrolysis 

    coupled: - deltaG
    Uncoupled: + delta G
  100. ATP hydrolysis release around -30 to -35 kJ/mol
  101. absorption of light by molecule requires a lot of conjugation
  102. as pressure increases solubility of gas increases

    solubility of gas higher at low temps
  103. cysteine is slightly acidic so PI more on that side
  104. lipoic acid deficiency could cause loss of pyruvate dehydrogenase activity which would lead to build up of pyruvate which would be converted to lactic acid instead of acetyl coa and then lactic acidosis
  105. neural crest - shwann cells peripheral nervous system
  106. Aromatic compounds are those that contain planar, conjugated rings and follow Hückel’s rule, which stipulates that the system must possess 4n + 2 π electrons. (To simplify this rule, remember that “n” denotes any integer, meaning that aromatic systems may contain 6, 10, or 14 π electrons, and so on.) Tyrosine, a classic example of an aromatic amino acid, fits all of these qualifications.
  107. free energy change of approximately zero. For this reason, this must be fairly easy to reverse. Thus, at equilibrium, an enzyme can easily catalyze both the forward and reverse reactions to keep the system in flux.
  108. Which of these scenarios constitutes a demonstration of the second law of thermodynamics? 

    A. A catabolic process may be coupled with an anabolic reaction, yielding a net increase in entropy. 

    The second law of thermodynamics states that a spontaneous reaction or cyclic process must yield a net entropy increase. In other words, the entropy of the universe should be continually rising.
  109. The goal of coupling is to make the total of the two reactions exergonic in nature.
  110. The synaptonemal complex is a protein-based linkage that appears during meiosis and connects homologous chromosomes. As these chromosomes must be closely situated to facilitate crossing over, issues could arise involving genetic recombination or synapsis.
  111. Sympatric speciation is that which occurs without a physical barrier. A population that diverges into two separate species in a single cave certainly falls under this form of speciation.

    A: Parapatric speciation occurs when segments of two distinct populations overlap. Due to environmental differences, these segments may develop into two species, but individuals in the overlapping areas can typically still interbreed.

    B, D: Allopatric speciation occurs when populations, or parts of the same population, are separated by a physical barrier. Peripatric speciation is a subtype of this concept that occurs specifically when one of the two populations is much smaller than the other.
  112. To proceed, gluconeogenesis must overcome the three irreversible steps that occur during glycolysis. Step 10 indicates the conversion of phosphoenolpyruvate to pyruvate. In gluconeogenesis, the reverse of this process requires catalysis by both PEP carboxykinase and pyruvate carboxylase.

    A: Step 1 involves the conversion of glucose to glucose 6-phosphate; during gluconeogenesis, this step is bypassed by glucose 6-phosphatase.

    B: In glycolysis, Step 3 is the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate. Gluconeogenesis involves the opposite transition, which is facilitated by fructose 1,6-bisphosphatase.
  113. B is correct. According to the Beer-Lambert law, absorbance = εCL. Here, ε represents the extinction coefficient, C denotes the concentration of the solution, and L stands for the path length in centimeters. Solving for ε gives a value closest to 0.8.
  114. All microtubules originate from microtubule-organizing centers, or MTOCs. These structures anchor the minus end of the microtubule to prevent its depolymerization. They also form the origin of the spindle apparatus during cell division.
Card Set
mcat science 9