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Flashcards in FL 1 Review Deck (44)
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31

What is the net number of ATP molecules synthesized by an obligate anaerobe per molecule of glucose?

This question cannot be answered from the passage so it is a "pseudo-discrete" question. An obligate anaerobe is an organism that must live WITHOUT oxygen in order to survive. Obligate anaerobes produce ATP via fermentation, which includes both glycolysis and the reactions necessary to regenerate the NAD+ necessary for glycolysis to continue. Fermentation leads to a net production of 2 ATP; this ATP is generated during glycolysis. Therefore, an obligate anaerobe will produce 2 ATP per molecule of glucose, which matches with choice (A).

32

Curve C on the graph below represents the normal hemoglobin dissociation curve at 38°C and physiological pH (7.4) . Which curve most likely corresponds to the hemoglobin dissociation curve for a patient suffering from acidosis (low blood pH)?

An increase in the concentration of hydrogen ions decreases hemoglobin's affinity for oxygen; that is, the binding of hydrogen ions to a molecule of oxyhemoglobin enhances the release of oxygen. According to the question, a patient suffering from acidosis has a decreased blood pH, which means that the concentration of hydrogen ions in the blood is higher than normal. And, as mentioned above, a high concentration of hydrogen ions means that hemoglobin will release oxygen more readily than it does under normal conditions. With reference to the hemoglobin dissociation curve, this means that at a given partial pressure of oxygen in the blood, the percent saturation of hemoglobin with oxygen in a patient with acidosis will be lower than it would be at physiological pH.

In terms of the graph, the hemoglobin dissociation curve corresponding to an acidotic patient would be shifted to the right of the curve for normal pH, and so curve D, choice (D), is correct.

33

Which of the following pieces of evidence would NOT support the hypothesis that mitochondria were once independent bacteria that eventually formed a symbiotic relationship with eukaryotic cells?

Many scientists believe that mitochondria were once independent unicellular entities, possibly prokaryotic in origin, which formed a symbiotic relationship with eukaryotic cells that was mutually beneficial to both parties. This theory is known as the endosymbiotic hypothesis. If mitochondria are believed to have been prokaryotic in origin, then any findings that reveal similarities between mitochondria and bacteria would support the hypothesis. The question asks which choice does NOT support the hypothesis. If choice (B) is true, and mitochondrial ribosomes more closely resemble those found in eukaryotes than those found in prokaryotes, then the hypothesis is not supported.

The other answer choices would all support the hypothesis:

Choice (A). The fact that mitochondrial DNA is circular and not enclosed by a nuclear membrane is a characteristic of bacteria. Bacteria have a single circular chromosome located in a region of the cell known as the nucleoid, which is not bound by a membrane. So (A) SUPPORTS the endosymbiotic hypothesis and is therefore incorrect.

Choice (C). The fact that there are many present-day bacteria that have symbiotic relationships with eukaryotic cells supports the concept that the mitochondrial ancestor could have lived within a eukaryotic cell in a mutualistic relationship because it proves that this idea is feasible and does in fact happen.

Choice (D). The fact that mitochondrial DNA codes for its own ribosomal RNA. provides evidence that at some point, mitochondria existed as free entities, capable of directing their own protein synthesis and cell division, and all the cellular activities associated with independently living organisms.

34

The L protein codes for a nucleic acid polymerase. Based on information in the passage, it most likely synthesizes:

The passage states that the virus does not integrate itself into the host genome, and it is not a retrovirus. Therefore, it does not need to synthesize DNA. Furthermore, it's stated that the rabies genome is RNA. Therefore, the only plausible answer is choice (D): it must synthesize RNA from RNA.

35

Which of the following is most likely to be true regarding cells in the muscles that spasm in a patient suffering from hydrophobia?

This question is asking for a true statement about the muscle cells that spasm in hydrophobia. The passage states that those cells are in the upper portion of the esophagus, which means that they are striated muscle cells. Striated muscle cells are voluntary, and therefore receive their innervation from the somatic division of the nervous system, thus Choice (D) is the correct answer.

Choice (A). Muscle contraction is dependent on release of calcium, not sodium.

Choice (B). Sarcomeres are a component of striated muscle, and so would be present.

Choice (C). The autonomic division of the nervous system innervates smooth muscle, which makes up the lower two thirds, not the upper portion, of the esophagus."

36

Recombination frequency

Recombination frequency is used to determine genetic distance, but cannot determine physical distance. If this is unclear, think about two alleles that are very far apart. The passage states that these alleles are likely to crossover multiple times; if a crossover event occurs an even number of times, the recombination frequency will appear to be zero. This thinking shows why choice (B) is correct: the recombination can make the alleles look closer together.

37

During meiosis II of spermatogenesis, nondisjunction of chromosome 4 occurs. The resultant gametes could contain:

Nondisjunction occurs when chromosomes fail to separate. Recall that during meiosis I, the maternal and paternal chromosomes separate; during meiosis II, the sister chromatids from one parent separate. If nondisjunction occurs during meiosis II of spermatogenesis, then you are likely to get two identical chromosomes of either maternal or paternal origin. Therefore, Roman numeral I is correct. However, if crossing over occurred during prophase I, then some of the maternal and paternal DNA was swapped, so two non-identical chromosomes with both maternal and paternal DNA would be found: Roman numeral II is correct. Now, we need to look at Roman numeral III. This is incorrect, since non-identical chromosomes must contain maternal and paternal information: in other words, crossing over between two paternal sister chromatids (if that were to happen) would still leave us with identical chromosomes

38

Which of the following does not derive from the neural crest?

Adrenal medulla
Schwann cells
Melanocyte cells
Erythrocyte cells


Since the neural crest is derived from the ectoderm, knowing all structure types that derive from ectoderm allow you rule out all choices except erythrocytes.

39

Based on the data in Table 1, what is the net charge on the five amino acids listed for S. cerevisiae tubulin at pH 7.4?

To answer this question, it's necessary to know the charges on the acids listed under S. cerevisiae in Table 1. The basic amino acids—which are positively charged at pH 7.4—are arginine and lysine. The acidic amino acids are aspartic acid and glutamic acid. Since none of these amino acids appear, the net charge on those five amino acids should be zero, which is choice (C).

40

The semi-permeable membrane of the dialysis machine functions in a manner most analogous to which part of the kidney?

The glomerulus, (A), functions like a sieve, allowing the filtration (movement from the circulation into the nephron tubule) of small molecules while blocking the filtration of the plasma proteins. The semi-permeable membrane serves an analogous function in the dialysis machine.

Choice (B) is wrong because the ureter is merely a tube connecting the kidney to the bladder.

Choice (C) is wrong because the descending loop of Henle does not serve a filtration function. The primary action of the descending loop is reabsorption of water.

Choice (D) is wrong because The vasa recta are the capillaries that supply nutrients to the nephron.

41

A patient with renal failure has nephrons which lack the ability to actively secrete or reabsorb any substances. Which of the following actions will the patient's kidney most likely still be able to perform?

Recall that the fluid in Bowman's capsule is isotonic to plasma. Without reabsorption or secretion, isotonic urine can still be produced. In other words, this patient's nephrons filter the blood at the glomerulus, but that initial filtrate then becomes urine without any further modification. This process will still allow excess salt to be removed from the body, because that salt diffuses through the glomerulus, which is still functioning in this patient. Therefore, choice (A) is correct.

42

Which of the following mitochondrial genome characteristics differs most from the characteristics of the nuclear genome?

Almost every base in mitochondrial DNA codes for a product.

43

Which of the following is a common trait of group I and group II introns that makes them different from introns that are not designated into a group number?

Group I and II introns are unique in that they are self-splicing, or do not involve protein enzymes in their splicing reactions. This definition is echoed by choice (D), the correct answer.

44

When action potential induces muscle contraction, which of the following occurs?

An action potential resulting in muscle contraction causes t-tubule depolarization, followed by SR release of Ca2+ in order for Ca2+ to bind to the troponin complex, thereby allowing tropomyosin to expose the myosin-binding sites on actin. This is described by choice (B).