MCAT - Chemical and Physical Foundations of Biological
Systems || with 100% Correct Answers.
Cytochrome c oxidase correct answers An enzyme responsible for electron transfer in the ETC,
so inhibiting it would slow or stop the ETC.
Dosing of Blast Phase Chronic Myeloid Leukemia (BP-CML) cells with cyanide would result in:
correct answers Reduced intercellular ATP and apoptosis or necrosis.
Cyanide binds to cytochrome c oxidase and prevents electron transfer. Inhibiting cytochrome C
oxidase would decrease ATP production. thus, large dose would also cause cell death (apoptosis
or necrosis).
Researchers also measure oxygen consumption and intercellular NADH levels in BP-CML cells
after exposure to pyrivinium. What did they most likely observe? correct answers An increase in
NADH levels and a decrease in O2 consumption.
According to the study, pyrivinium inhibits intracellular signaling, is effective against cancer
cells and involves heavily in the inhibition of mitochondrial respiration. Because MR consumes
oxygen, pyrivinium should reduce oxygen consumption.
NADH supplies electrons to the ETC, so if the ETC is not functioning properly, the NADH
produced by the citric acid cycle would not be OXIDIZED to NAD+ and H+.
NADH correct answers Its oxidized form is (NAD+) and reduced for is (NADH).
Compounds that decouple the proton gradient across the inner mitochondrial membrane would:
correct answers Not have a strong effect on cells exposed to pyrivinium.
Decoupling the proton gradient across the inner mitochondrial membrane would be redundant in
pyruvinium-exposed cells, since MR is already functioning poorly.
Which of the following would best explain the observation that pyrivinium is more effective
against BP-CML than colon cancer? correct answers Colon cancers rely less on glycolysis for
energy production than BP-CML.
According to the study, pyrivinium is effective against cancers in glucose-starvation conditions.
Therefore, if colon cancers rely less on glycolysis then we would expect pyrivinium to be less
effective against colon cancers and thus more effective against BP-CML.
Which of the following best describe why hyperventilation would lead to a decreased blood CO2
concentration? correct answers The rate of CO2 exhalation exceeds the rate of CO2 production
in the cells.
,The main source of CO2 in the human body is cellular production during the Krebs cycle. If an
individual breathes very rapidly, he will exhale CO2 more quickly than his cells produce it.
pH correct answers The pH of a buffer solution can be calculated by pH= pKa + log [conjugated
base]/ [acid]
Which of the following best describes how a shift to the right in the dissociation curve results in
more oxygen delivered to tissue? correct answers (Question #6) The distance between the curves
at 100mmHg is less than the distance between the curves at 40mmHg.
When the curve is shifted to the right, the oxygen affinity of hemoglobin at high partial pressure
is less affected than it is at lower pressures.
At a PO2 of 100mmHg, the difference in % saturation between a normal and a right shifted curve
is minimal, but at 40 mmHg, the difference is more profound. As a result, the amount of oxygen
that each red blood cell picks up in the alveoli of the lungs is not significantly decreased, but the
amount of oxygen release in the tissues increases markedly.
Note: in the lungs, hemoglobin picks up O2 from the alveoli, but in the tissue, the affinity for
oxygen must be lowered so that it can diffuse into the tissues.
Relationship between pH and Oxygen Affinity correct answers When pH increases, hemoglobin
binds oxygen more readily and vice versa.
In RBC, bicarbonate can be exchanged for chloride in plasma. Why do RBC in venous
circulation have a higher concentration of chloride ions? correct answers Answer: Higher
concentration of CO2 in venous erythrocytes produce bicarbonate and drive the exchange of Cl-
from the plasma into the cell.
The question stem tell us the RBC can exchange chloride from the plasma with bicarbonate
anions. When more bicarbonate is available, there should thus be a higher concentration of
chloride ions in the cells.
Know that an increase in CO2 corresponds to an increase in bicarbonate concentration in
erythrocytes, more chloride should take its place.
Most CO2 is not found in the plasma.
Also, know that hyperventilation results in CO2 being expelled from the blood causing the pH to
rise. In response, the buffer needs to release more H+ to lower the pH back to physiological
norms.
Which of the following cannot explain a patient who present with a blood pH of 7.0
A. Anaerobic respiration leading to lactic acid buildup
, B. Hypoventilation
C. Carbonic anhydrase working only in the reverse direction
D. Underproduction of bicarbonate correct answers Answer: C
A blood pH of 7.0 is very low (normally 7.4). Thus, it must be attributed to a mechanism that
will increase hydrogen ion concentration. Therefore, the correct answer will be one that would
have an opposite effect on pH or no effect.
We know that carbonic anhydrase catalyzes the reaction in H20 + CO2 <->H2CO3 <->H+ +
HCO3-
Thus, if carbonic anhydrase only worked in the reverse direction, there would be more CO2 and
H20 and less H+ in the blood. Therefore, blood pH would increase. (Not a decrease in pH).
It's not A, because lactic acid is acidic.
It's not B, because hypoventilation result in respiratory acidosis, which would lower the pH.
It's not D, because bicarbonate is a weak base, so decrease bicarbonate production would be
expected to make the blood less basic.
A medical student assisting with the research is interested in applying the results of the
experiment to spinal cord injury in humans. The principal investigator responds that this study
does not apply to such injury, why? correct answers (Question #9) the study only examined the
behavior of macrophages in response to uninjured nerve cells and astrocytes.
According to the passage, macrophages are responsive to cues in their microenvironments. the
site of an injury produces a very different microenvironment from resting tissues. The study
looked only at macrophage migration in response to conditioned media from resting nerve cells
or astrocytes.
Multiple Sclerosis (MS) is an autoimmune disease in which the myelin sheath is attacked. Based
on this study, which of the following approaches will provide the best treatment for this disease?
correct answers Treat classically activated (CA) macrophage with anti-CR-3 to block
phagocytosis.
According to the passage, CA macrophages phagocytose (or damage) myelin. Thus, blocking the
phagocytosis of myelin using the anti-CR3 antibodies would reduce the harm done by
inappropriately activated CA macrophages to the myelin sheath.
Myelin correct answers A substance that coats the axons of some neurons. Myelin acts to
increase the conduction velocity.
Which additional control experiment would allow the researcher to conclude that the
macrophage migration difference in NCM and ACM are due primarily to chemoattractant in the
medium? correct answers The migration of both CA and AA phenotypes towards MCP-1, a
potent chemoattractant of macrophages, should be measured.
