An enzyme catalyst is kept in a solution buffered to the pH that maximizes activity for those enzymes found in the blood. The enzyme catalyzes a reaction that produces an acid whose pKa is 4.5. In this buffer solution, the acid product will be:
Answer(s): A
The blood has a pH around 7.4, making it somewhat basic. If this enzyme is in a solution buffered to a point to maximize enzymes found in the blood, then the buffer solution will have a pH of 7.35 to 7.45. When an acid is in a solution whose pH is higher than its pKa, the acid is deprotonated, making choice (A) the correct answer.B: The acid would be protonated if the buffer solution had a pH that was below 4.5.C: The acid would have equal concentrations of the acid and conjugate base form if the buffer had a pH of around 4.5.D: There's no reason for us to assume the product wouldn't form.
Noncompetitive inhibition differs from uncompetitive inhibition in that a noncompetitive inhibitor binds to an allosteric site on the enzyme and prevents it from catalyzing a reaction, whereas uncompetitive inhibitors bind to the enzyme-substrate complex and prevent catalysis. Increasing the substrate concentration would have which of the following effects?
Answer(s): C
As substrate concentration increases, there will be more binding between the substrate and the enzyme. More enzyme-substrate complex in solution means more opportunity for an uncompetitive inhibitor to bind. Thus, as substrate concentration increases, the impact of an uncompetitive inhibitor would be expected to increase.A: The concentration of a noncompetitive inhibitor isn't changed by changing the substrate concentration.B, D: As discussed above, the impact of an uncompetitive inhibitor would be increased.
A certain molecule acts by cytochrome oxidase A3, the final enzyme in the electron transport chain. Administration of a large dose of this substance to a human would likely:
The electron transport chain works by taking high-energy electrons from molecules like NADH and passing them through a series of enzymes, ultimately ending with oxygen as the final electron acceptor. If this chain is blocked, aerobic respiration would cease, killing the cell. Eukaryotic cells in humans cannot survive using only anaerobic respiration. Thus (A) is the right answer. Several poisons work in the manner described, most notably cyanide.B: ADP is produced when cells use up ATP to carry out cell functions. Blocking the electron transport chain would have no effect on ADP's immediate availability.C: As discussed above, this poison would kill the person.D: As discussed above, this poison would kill the person.
Myoclonic epilepsy and ragged-red fiber (MERRF) is an extremely rare disorder that affects neuromuscular systems. MERRF results from a mutation in mitochondrial DNA (mtDNA) that impairs protein synthesis, oxygen consumption, and energy production. When an affected male and a normal female reproduce, which of the following best predicts the expected phenotypic ratios of the offspring?
This question is asking the examinee to determine offspring phenotypes for a gene that is located on mitochondrial DNA. Since mtDNA follows maternal inheritance, all the offspring receive their mitochondrial DNA from the mother. In this case, the MERRF-causing mutation is located on the father's mtDNA. Therefore, the mutations are not passed on to the offspring. Since all of the offspring will receive functioning mtDNA from the mother, none of the offspring will inherit mutated genes causing MERRF. Thus, answer choice A correct.
A person suffering from severe dehydration and starvation would NOT be expected to have elevated plasma concentrations for which of the following hormones?
Answer(s): D
This question asks you to determine the body's physiological response to the extreme conditions of dehydration and starvation. In such cases, the person would be expected to have low blood pressure and low nutrients (i.e.proteins, carbohydrates, and lipids). As a result, the body will respond by producing hormones that increase blood pressure and mobilize stored nutrients (glycogen, fat, etc.). ADH and aldosterone both increase blood pressure so they would be expected to appear in high plasma concentrations in response to the low blood pressure, eliminating choices A and C. Cortisol would be expected in high plasma to increase carbohydrate, protein, and fat availability, making B false. That leaves answer choice D. Insulin lowers blood glucose levels, which is expected to appear in the blood after a sugary meal. In the case of starvation, the body would respond by increasing blood glucose levels via the production of glucagon.
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