MCA T Biological Sciences Review MCAT Bioloqy Chapter Title
Corresponding MCA T Science Workbook Passage Numbers
Molecular Biology Microbiology Generalized Eukaryotic Cells Genetics and Evolution Nervous and Endocrine Systems Circulatory, Lymphatic, and Immune Systems Digestive and Excretory Systems Muscle and Skeletal Systems Respiratory and Skin Systems Reproductive Systems and Development
PHYSICS
Chapter Number
MCAT Physical Sciences Review MCAT Physics Chapter Title
Kinematics Mechanics i Mechanics I I Mechanics I II Fluids and Elasticity of Solids Electrostatics Electricity and Magnetism Oscillations and Waves Sound Light and Geometrical Optics
GENERAL CHEMISTRY
Chapter Number
MCA T Physical Sciences Review MCAT General Chemistry Chapter Title
Corresponding MCA T Science Workbook Passage Numbers
Atomic Structure Periodic Trends and Bonding Phases Gases Solutions Kinetics Equilibrium Acids and Bases Thermodynamics Redox and Electrochemistry
Structure and Bonding Substitution and Elimination Reactions Electrophilic Addition Reactions Nucleophilic Addition/Cycloaddition Reactions Lab Techniques and Spectroscopy Biologically-Important Organic Chemistry
PERIODIC TABLE OF THE ELEMENTS
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MCAT BIOLOGY
Passage 1 (Questions 1-9)
Many membrane transport processes are not driven directly by the hydrolysis of ATP. Instead, they are coupled to the flow of an ion down its electrochemical gradient. For example, glucose is transported into some animal cells by the simultaneous entry of Na+. Sodium ions and glucose bind to a specific transport protein and enter together. A protein responsible for the concerted movement of two such species is called a symport. An antiport carries two species in opposite directions. The rate and extent of glucose transport depends on the Na+ gradient across the plasma membrane. Sodium ions entering the cell in the company of glucose are pumped out again by the Na+/K+ ATPase pump,
A group of researchers wished to gain information about a type of bacteria that was known to take in glucose across its cell membrane by use of a sodium-glucose cotransport mechanism. The researchers conducted two experiments in which bacterial cells were placed in glucose-containing media that differed with respect to relative ion concentration and ATP content. Glycolysis was inhibited in the cells during these experiments.
Experiment 1:
Bacterial cells with relatively low intracellular sodium concentration were placed in a glucose-rich medium that had a relatively high sodium concentration but no ATP. At regular time intervals, the medium was analyzed for glucose concentration and sodium concentration. See Figure 1.
x time - x
time - Figure 1 Glucose and Na+ concentrations in medium
(no ATP in medium)
Experiment 2:
Bacterial cells with relatively low intracellular sodium concentration were placed in a glucose-rich medium that had a relatively high sodium concentration and that was also rich in ATP. At regular time intervals, the medium was analyzed for glucose, sodium, and ATP concentration. See Figure 2. If radiolabeled ATP is used in this experiment, the majority of the radiolabel at the end of the experiment is found as ADP inside the cells.
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Graph III
ÑÑÑÑÑÑÑ JC
time -
Graph IV
IÑÑÑÑÑà x
time -
x time -
Figure 2 Glucose, Na*, and ATP concentrations in medium
1. Within animal cells, the transport of Na+out of the cell by the Na+/K+ ATPase pump involves:
A. symport. B. antiport. C. facilitated diffusion. D. active transport.
2. The results of Experiments 1 and 2 suggest that the cells take up glucose:
A. in exchange for ATP, as long as extracellular sodium concentration remains constant.
B. in exchange for sodium, as long as ATP concentration is zero.
C. together with sodium, as long as a favorable sodium concentration gradient is maintained.
D. together with sodium, as long as extracellular ATP concentration is increasing.
3. On the basis of Experiments 1 and 2, a researcher hypothesized that all of the cells under study ultimately depend on energy to operate the sodium-glucose cotransport mechanism. Is this hypothesis reasonable?
A. No; Figure 1 indicates that glucose can cross the cell membrane indefinitely in the absence of exogenous energy.
B. No; Figure 2 indicates that extracellular glucose and ATP concentrations are independent.
C. Yes; Figure 1 indicates that a sodium gradient drives glucose transport, and Figure 2 indicates that ATP maintains the sodium gradient.
D. Yes; Figures 1 and 2 indicate that glucose crosses the cell membrane in exchange for phosphate.
4. The results of Experiments 1 and 2 indicate that ATP promotes the cellular uptake of glucose by serving as a source of:
A. enzymes. B. metabolic energy. C, inorganic phosphate. D. carbohydrate.
5. If, in Experiment 1. ATP had been added to the medium at time x, which of the following would represent the appearance of Graphs I and II?
Graph I
L time -
Graph I L ÑÑÑÑÃ
x time -
x time -
1 Graph I
Graph I1
b I x
time -
x time -
x time -
x time - x
time -
6. A student postulated that the glucose transport protein must be located exclusively on the outer surface of the cell membrane. Is this hypothesis necessarily true?
A. Yes; transport proteins only occur on the outer surface of membranes.
B. Yes; the hydrophobic tails of the lipid bilayer repel protein molecules.
C. No; transport proteins are located exclusively on the inner surface of the lipid bilayer.
D. No; transport proteins may span the entire width of the lipid bilayer.
7. According to Figure 1, as sodium concentration in the medium approaches the same concentration found in the cells, glucose concentration in the medium would:
A. remain at its original level, because sodium concentra t ion does not af fec t glucose concentration.
B. increase, because less glucose is transported into the bacterial cells.
C. level off, because a sodium gradient is not available to drive cotransport.
D. approach zero, because glucose and sodium are transported together.
8. In Figure 1, if the initial Na+ concentration in the medium were doubled, which graph below would best depict the glucose concentration in the medium?
x t ime .
time -
x tune -
x time -
9. Based on the information in the passage, the first step in the transport of sodium and glucose into a cell is:
A. binding of specific secreted proteins to sodium in the surrounding medium.
B. direct hydrolysis of ATP in the cytoplasm by the sodium-glucose cotransporter.
C. direct hydrolysis of ATP on the extracellular surface by the sodium-glucose cotransporter.
D. binding of specific proteins in the membrane to sodium and glucose in the surrounding medium.
Passage 2 (Questions 1-7)
Protein synthesis occurs either on free ribosomes o r ribosomes bound to the endoplasmic reticulum (ER). According to the signal hypothesis, it is the growing polypeptide that cues the ribosomes to remain free or attach to the ER. Proteins targetted to the ER, Golgi, lysosomes, plasma membrane, or to be secreted contain a signal peptide of 15 or more continuous amino acids. These N-terminus signal peptides are responsible for the co-translational insertion of the growing polypeptide into the membrane of the ER. After the leading end of the protein is inserted into the ER lumen, the signal peptide is cleaved by an enzyme.
Proteins destined for the secretory pathway are packaged into vesicles that pinch off from the membrane of the ER and fuse with the cis face of the Golgi apparatus. Often the packaging of a protein into a transport vesicle requires the presence of a region on the protein that is recognized by a receptor in the Golgi membrane. This receptor-protein complex will localize to a vesicle and target the vesicle to its destination.
One of the best-characterized pathways of vesicular transport involves proteins destined to become lysosomal enzymes. These proteins carry a unique mannose-6-phosphate (M6P) marker that is recognized by the specific M6P receptor in the membrane of the Golgi apparatus. M6P receptors bind proteins and sequester them along one region of the Golgi membrane, facilitating their packaging into vesicles. Once the vesicle has budded from the Golgi apparatus, it travels to the lysosome, where it fuses with the lysosomal membrane. The M6P receptor releases its bound protein when it encounters the acidic pH of the interior of the lysosome. The acidity of the lysosome also activates lysosomal enzymes.
1. Proteins that are to be secreted pass through what series of organelles?
A. ER Ñ Golgi Ñ lysosomes Ñ plasma membrane B. ER 4 Golgi -+ secretory vesicles C. cytoplasm -+ Golgi 4 ER Ñ .secretory vesicles D. ER Ñ secretory vesicles Ñ lysosomes
2. Where in the cell would the M6P receptor be transcribed?
A. In the nucleus B. In the cytoplasm C. In the rough ER D. In the Golgi
3. The transport of proteins to the lysosomes requires which of the following?
A. Acidic pH in the ER B. Vesicle movement from the rough ER to the Golgi C. Endocytosis D. Inhibition of signal peptidase
4. Which of the following enzymes would be expected to function well within an acidic environment?
A. Signal peptidase B. Trypsin C. Pepsin D. Pancreatic lipase
5. Which of the following processes would be disrupted in a cell that failed to label proteins with the M6P marker?
A. Intracellular digestion of macromolecules B. Protein synthesis C. Oxidative phosphorylation D. Golgi formation
6. If a protein that is destined to become a lysosomal enzyme were synthesized without a signal peptide, in which of the following cellular regions would it ultimately reside?
A. The cytosol B. The cell surface C. The mitochondria D. The peroxisomes
7. The ER lumen corresponds most closely to which of the following compartments?
A. The interior of the nucleus B. The cytoplasm C. The extracellular environment D. The intermembrane space in mitochondria
Passage 3 (Questions 1 - 6 )
The circulation of a fetus differs from that of a newborn infant in several important aspects.
First, unlike an infant's anatomy, fetal anatomy does not provide direct contact between the fetus and the external environment. The lungs of the fetus are collapsed and fluid- filled, and do not function in respiration. Fetal respiration, nutritional and excretory functions are all performed by the placenta, which is essentially composed of interwoven fetal and maternal capillaries. Maternal blood, however, does not normally mix with fetal blood.
Second, both sides of the fetal heart supply blood to the systemic circulation; hence, they work largely in parallel, rather than in series as in an infant. While the lungs are fluid- filled, the pulmonary vascular resistance is higher than the- systemic vascular resistance. Shunts between the left and right atria and between the great arteries permit most of the blood to bypass the lungs.
Third, the fetus exists in hypoxic conditions relative to those that exist after birth. To reach the fetal blood, oxygen must diffuse through the placenta from the maternal blood which has already oxygenated a substantial portion of . maternal body tissue. The blood that perfuses the fetus is about 67% saturated with oxygen. In the normal person, this is the approximate saturation of mixed venous blood returning to the lungs to be oxygenated. Blood that leaves the lungs of the normal adult is about 95% to 98% saturated with oxygen. The lowest oxygen saturation of blood in the fetal circulation occurs in blood in the lower inferior vena cava. In the fetal lamb, which furnishes a good model for the study of human fetal circulation, oxygen saturation of blood in the lower inferior vena cava is 26%. Blood in the superior vena cava, which comes mostly from the head, is only 3 1% saturated in the human fetus,
The fetus has two adaptations for surviving relative hypoxia: its cellular enzymes can function at low oxygen tensions, and fetal hemoglobin can deliver oxygen to the tissues despite low levels of oxygen saturation. These special properties are lost within a few days after birth, when normal respiratory activities begin.
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The brain of the human fetus is large relative to the rest of the body, and its supply of oxygen is very important. The fetal brain is perfused with highly-saturated blood from the left ventricle. The output of the right ventricle, which is less saturated, supplies the limbs and internal organs of the fetus.
1. At the placenta, C O should normally:
A. diffuse from the fetal side to the maternal side. B. diffuse from the maternal side to the fetal side. C. be of equal concentration on both the maternal and
fetal sides. D. be of higher concentration on the maternal side
with no net diffusion between the maternal and fetal sides.
2. Some children persist in forming fetal hemoglobin for months or even years after birth. Such children would likely:
A. be able to withstand environments having low oxygen content.
B. be able to shunt blood from the right to the left side of the heart.
C. be unable to survive in the absence of an artificial oxygen supply.
D. be unable to bear children.
3. A newborn infant is able to survive the loss of fetal hemoglobin within a few days after birth because the infant's:
A. blood continues to bypass the fluid-filled lungs. B. circulatory system is independent of the mother's. C. lungs have direct contact with oxygen in the
environment. D. digestive and excretory systems become active.
4. In a pregnant woman with healthy lungs but impaired circulation, her fetus may be at risk of suffering birth defects because:
A. the placenta will show increased material perfusion. 3. the fetus cannot tolerate any compromising of the
blood supply to its internal organs. C. the maternal alveoli may be deficient in oxygen
partial pressure. D. fetal oxygen supply depends on maternal
circulation.
5. Blood delivered to the fetus has a lower oxygen concentration than does blood leaving the adult lung because, before it reaches the placenta, maternal blood:
A. mixes with fe ta l blood of lower oxygen concentration.
B. releases oxygen to the mother's own tissues. C. gives up nutrients to the fetal circulation. D. must pass through the right atrium and ventricle.
6. Which of the following chambers of the fetal heart supply blood to the systemic circulatory system?
A. Right atrium and right ventricle B. Right atrium and left atrium C. Left ventricle and right ventricle D. Left ventricle and right atrium
Passage 4 (Questions 1-6)
The selective permeability of cell membranes plays an important role in regulating the intracellular environment. Ions can be transported across cell membranes by passive, active, or facilitated processes.
Ionophores are small hydrophobic molecules that dissolve in the lipid bilayer and increase its ion permeability. Most are synthesized by microorganisms, presumably as biological weapons, and some have been used as antibiotics. They have been widely employed by cell biologists to increase membrane permeability to specific ions in studies on synthetic bilayers, cells, and cell organelles.
It is known that ionophores may be substance-specific. That is, a given ionophore may promote cell membrane permeability to one substance, but not to another.
An investigator sought to learn more about the charac- teristics of a particular ionophore termed lonophore A.
Experiment 1 :
Cells with relatively high internal calcium concentration and low internal magnesium concentration were placed in an aqueous medium of relatively low calcium concentration and high magnesium concentration.
After several seconds had elapsed, the cells' internal ion concentrations were evaluated, and it was found that internal concentrations of calcium and magnesium had remained the same.
Experiment 2 :
Experiment 2 was identical to Experiment 1 except that the cell medium was infused, also, with Ionophore A.
The cells' internal ion concentrations were evaluated, and it was found that the internal concentration of calcium had remained the same but that the internal concentration of magnesium had increased subs tantially.
1. Across which of the following cell types would the inward diffusion of water be most pronounced under normal conditions?
A. Epithelial cells of the stomach B. Epithelial cells of the large intestine C . Endothelial cells of the alveolar capillaries D. Cornified cells of the skin
2. If, in Experiment 1, the cells were placed in a hypotonic medium, and if the cells were permeable to water and magnesium, then the cells would most likely have:
A. increased in calcium concentration to compensate for a deficit in positive charge.
B. decreased in calcium concentration by intake of water.
C. decreased in size by losing both calcium and magnesium ions.
D. decreased in size by losing water passively along a concentration gradient.
3. A graduate student suggested that a neuron at resting potential might be induced to undergo an action potential by exposure to a sodium-specific ionophore. Is this a reasonable hypothesis?
A. Yes, the ionophore would excite a threshold reaction i n the neuron's Schwann cells.
B. Yes, an action potential occurs when threshold depolarization causes voltage-gated channels to open.
C. No, an action potential requires a reduced permeability to sodium ions.
D. No, an action potential is triggered by active transport of sodium along the myelin sheath.
4. If, in either Experiment 1 or Experiment 2, the cells had decreased their internal concentration of magnesium, it would indicate that they had undergone a process in which:
A. ATP had been converted to ADP. B. Ca2+ entered the cell. C. carbohydrates had been synthesized. D. ~ol tage~ga ted ion channels had opened.
5. The results of Experiments 1 and 2 would most justify the researcher's conclusion that:
A. Ionophore A would not be a useful antibiotic. B. Ionophore A is specific to positively-charged ions,
since it altered sodium permeability but not magnesium permeability.
C. ionophores facilitate movement only in accordance with existing concentration gradients.
D. in order to be effective, ionophores require the active assistance of the cell's sodium-potassium
pump.
6. If a given cell were persistently engaged in active transport, its cytoplasm would most likely be rich in:
A. smooth endoplasmic reticulum. B. lysosomes. C. centrioles. D. mitochondria.
Questions 1 through 1 1 are NOT based on a descriptive passage.
1. All of the following are key processes in the production of energy in the mitochondrion EXCEPT:
A. glycolysis. B. the citric acid cycle. C. electron transport. D. oxidative phosphorylation.
2. When it is time to breed, salmon travel from saltwater, in which they are hypotonic, to freshwater, in which they are hypertonic. They maintain solute balance by reversing their osmoregulatory machinery when moving between the two environments. Failure to reverse this machinery when moving to their breeding grounds would most likely result in:
A. death, as cells became too concentrated to carry out normal metabolism.
B. death, as cells underwent lysis due to water influx. C. improved metabolic activity, as enzyme
concentrations increased. D. no change, because movement from a hypertonic
to a hypotonic medium does not present osmotic challenges.
3. A hormone is discovered that rapidly accumulates inside renal cells in the absence of endocytosis when administered to mice intravenously. The hormone is most likely a:
A. polypeptide. B. steroid. C. second messenger. D. neurotransmitter.
4. The ratio of guanine-cytosine (G-C) pairs to adenine- thymine (A-T) pairs is useful in laboratory manipulation of double-stranded DNA. If a segment of DNA has a low G-C : A-T ratio, it would be reasonable to assume that this segment would:
A. contain more guanine than cytosine. B. contain more adenine than thymine. C. require more energy to separate the two DNA
strands than would a comparable segment of DNA having a high G-C : A-T ratio.
D. require less energy to separate the two DNA strands than would a comparable segment of DNA having a high G-C : A-T ratio.
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5. What organelle would be most closely associated with exocytosis of newly synthesized secretory protein?
A. Lysosomes B. Golgi apparatus C. Perbxisomes D. Ribosomes
6. It is known that the developing frog embryo requires greater protein production than the adult organism. If cells from a developing frog embryo and from a mature frog were examined, would the investigator find the greater rate of translation in cells of the embryo or of the adult?
A. Embryo, because a developing organism requires a higher rate of translation than does an adult
B. Embryo, because ribosomal production is not yet under regulatory control by DNA
C. Adult, because ribosomal productio.n is more efficient in a mature organism
D. Adult, because a mature organism has more complex metabolic requirements
7. Colchicine is a compound which interferes with the formation of microtubules. Which of the following would be affected LEAST by the administration of colchicine?
A. Mitotic spindles B. Flagellae C . Organelle movement D. Amoeboid motility of cells
8. Clathrin, a substance that aggregates on the cytoplasmic side of cell membranes, is responsible for the coordinated pinching off of membrane in receptor- mediated endocytosis. A lipid-soluble toxin that inactivates clathrin would be associated with:
A. reduced delivery of polypeptide hormones to endosomes.
3. increased secretion of hormone into t.he extracellular fluid.
C. increased protein production on the rough endoplasmic reticulum.
D. an increase in ATP consumption.
9. In Kartagener's syndrome, defective dynein is produced causing a paralysis of microtubule-based movement of flagellae and cilia. One could expect to find all of the following outcomes EXCEPT:
A. male infertility. B. ectopic pregnancy in women. C. chronic lung infections. D. failure to ovulate in women.
10. If erythrocytes are placed into a hypertonic solution, they will:
A. hemolyze. B. remain the same. C . swell up. D. shrivel.
11. A codon is a segment of an mRNA molecule that codes for one amino acid in a polypeptide chain formed during protein synthesis. Which of the following correctly describes the chain of events that occurs in the synthesis of a polypeptide?
A. Specific RNA codons cause amino acids to line up in a specific order; tRNA anticodons attach to mRNA codons; rRNA codons cause protein molecules to cleave into specific amino acids.
B. DNA generates mRNA in the nucleus; mRNA moves to the cytoplasm and attaches to a tRNA anticodon; an operon regulates the sequence of events that causes amino acids to line up in their appropriate order.
C. DNA generates tRNA; the tRNA anticodon attaches to the mRNA codon in the cytoplasm; tRNA is carried by mRNA to the ribosomes, causing amino acids to join together in a specific order.
D. DNA generates mRNA; mRNA moves to the ribosomes, where a tRNA anticodon binds to an mRNA codon, causing amino acids to join together in their appropriate order.
