When humans are submerged in water, the mammalian dive reflex acts to alter circulation. Heart rate decreases, blood flow to the extremities is reduced, and mean arterial blood pressure is increased. These accommodations lead to:
Answer(s): B
The question stem describes the effects of the mammalian dive reflex, indicating that blood flow to the extremities is reduced. This would increase heat retention of the body.Choice A is incorrect because oxygen demand by the tissues depends on the metabolic rate of the tissues, which is not affected by changes in blood pressure, heart rate, or blood flow to the extermities.Choice C is incorrect because the dive reflex will not lead to a decrease in oxygen partial pressure. The partial pressure of oxygen will decrease during a dive because the individual is holding their breath, not because of the accommodations of the dive reflex.Choice D is incorrect because venous return, the amount of blood returned to the heart by the venous circulation, will not be increased. If stroke volume (the volume of blood pumped with each beat) remains constant, the decrease in heart rate caused by the dive reflex would lead to a decrease in venous return.
In 1972, Georges Ungar reported the discovery of a peptide that appeared to transfer learning. Ungar's claim was based on experiments in which rats placed in a chamber with specially designed dark and light regions were trained to avoid the dark regions of the chamber. Following their training, the rats were killed and brain extracts were prepared. These brain extracts were injected into naive rats which were then observed to acquire the fear of darkness without training. Two hypotheses were proposed to explain these remarkable results:Hypothesis 1Ungar concluded that the extracts contained some chemical that transmitted the learned fear of darkness to the naive rats. A fifteen amino-acid polypeptide was isolated from the brain extracts and sequenced. Ungar claimed that this peptide, called scotophobin, was a chemical transmitter of learning. The peptide had the primary structure shown below:C-ser-asp-asn-arg-gln-gln-gly-lys-ser-ala-arg-gln-glygly-tyr-NscotophobinHypothesis 2Other researchers, who tested scotophobin but could not reproduce Ungar's results, argued that scotophobin did not transfer the learned fear of darkness. Instead, they suggested that scotophobin, which is structurally similar to ACTH and vasopressin, acted to increase stress in the rats. Since stress increases sympathetic nervous activity, rats injected with scotophobin would become hyperactive and tend to spend less time in the dark regions of the experimental chamber. They argued that such stress responses in the rats could be misinterpreted as a fear of darkness. Ungar's claim was further weakened by chemical analysis in which both the scotophobin extracts which Ungar had injected into the naive rats and a sample of synthesized scotophobin peptide were subjected to SDS polyacrylamide gel electrophoresis, as shown in Figure 1. Figure 1Hydrolytic enzymes cleave polypeptides at specific amino acid residues. Which of the following hydrolytic enzymes could be used to cleave scotophobin into three fragments?
Answer(s): D
In order to cleave scotophobin into three fragments, the protein must be cleaved at two sites. Clositripain will cleave scotophobin at both Arg residues, while pepsin will cleave scotophobin at the Asp residue and at the Tyr residue. Note that the enzymes cleave at the carboxy end of the residue. Thus, according to the direction in which the sequence of the protein is written in the text (carboxy to amino end), the enzymes will cleave before,E. e., to the left of, the specified amino acid residue.Choice A and B are incorrect because trypsin will cleave the peptide at two Arg location and one Lys location, creating 4 fragments.Choice C is incorrect because chymotrypsin will cleave the peptide at a single point (Tyr), creating 2 fragments.
In 1972, Georges Ungar reported the discovery of a peptide that appeared to transfer learning. Ungar's claim was based on experiments in which rats placed in a chamber with specially designed dark and light regions were trained to avoid the dark regions of the chamber. Following their training, the rats were killed and brain extracts were prepared. These brain extracts were injected into naive rats which were then observed to acquire the fear of darkness without training. Two hypotheses were proposed to explain these remarkable results:Hypothesis 1Ungar concluded that the extracts contained some chemical that transmitted the learned fear of darkness to the naive rats. A fifteen amino-acid polypeptide was isolated from the brain extracts and sequenced. Ungar claimed that this peptide, called scotophobin, was a chemical transmitter of learning. The peptide had the primary structure shown below:C-ser-asp-asn-arg-gln-gln-gly-lys-ser-ala-arg-gln-glygly-tyr-NscotophobinHypothesis 2Other researchers, who tested scotophobin but could not reproduce Ungar's results, argued that scotophobin did not transfer the learned fear of darkness. Instead, they suggested that scotophobin, which is structurally similar to ACTH and vasopressin, acted to increase stress in the rats. Since stress increases sympathetic nervous activity, rats injected with scotophobin would become hyperactive and tend to spend less time in the dark regions of the experimental chamber. They argued that such stress responses in the rats could be misinterpreted as a fear of darkness. Ungar's claim was further weakened by chemical analysis in which both the scotophobin extracts which Ungar had injected into the naive rats and a sample of synthesized scotophobin peptide were subjected to SDS polyacrylamide gel electrophoresis, as shown in Figure 1.Figure 1In a follow-up experiment, researchers administered scotophobin to rats in order to examine its physiological effects. Which of the following observations of physiological effects in the rat would provide the best support for Hypothesis 2?
Answer(s): C
Hypothesis 2 states that scotophobin, which is similar to ACTH and ADH, increases sympathetic activity. Thus, any observation of ACTH or ADH-like effects, or of increased sympathetic activity (fight-or-flight) would support Hypothesis 2. Only Choice C, increased heart rate, is a result of increased sympathetic activity.Choice A is incorrect because ADH-like activity would tend to decrease urine volume by increasing water reabsorption in the collecting duct of the nephron.Choice B is incorrect because, although sympathetic activity will lead to pupil dilation, if this causes the rats to prefer darkness then it does not support Hypothesis 2 which tries to explain why an increase in sympathetic activity would cause the rats to avoid darkness.Choice D is incorrect because sympathetic activity will tend to decrease blood flow to the digestive tract.Dilating arterioles would increase blood flow. Also, vasopressin acts to constrict blood vessels and increase blood pressure.
In 1972, Georges Ungar reported the discovery of a peptide that appeared to transfer learning. Ungar's claim was based on experiments in which rats placed in a chamber with specially designed dark and light regions were trained to avoid the dark regions of the chamber. Following their training, the rats were killed and brain extracts were prepared. These brain extracts were injected into naive rats which were then observed to acquire the fear of darkness without training. Two hypotheses were proposed to explain these remarkable results:Hypothesis 1Ungar concluded that the extracts contained some chemical that transmitted the learned fear of darkness to the naive rats. A fifteen amino-acid polypeptide was isolated from the brain extracts and sequenced. Ungar claimed that this peptide, called scotophobin, was a chemical transmitter of learning. The peptide had the primary structure shown below:C-ser-asp-asn-arg-gln-gln-gly-lys-ser-ala-arg-gln-glygly-tyr-NScotophobinHypothesis 2Other researchers, who tested scotophobin but could not reproduce Ungar's results, argued that scotophobin did not transfer the learned fear of darkness. Instead, they suggested that scotophobin, which is structurally similar to ACTH and vasopressin, acted to increase stress in the rats. Since stress increases sympathetic nervous activity, rats injected with scotophobin would become hyperactive and tend to spend less time in the dark regions of the experimental chamber. They argued that such stress responses in the rats could be misinterpreted as a fear of darkness. Ungar's claim was further weakened by chemical analysis in which both the scotophobin extracts which Ungar had injected into the naive rats and a sample of synthesized scotophobin peptide were subjected to SDS polyacrylamide gel electrophoresis, as shown in Figure 1.Figure 1Researchers isolated a polypeptide from the brains of goldfish trained to avoid darkness. This goldfish scotophobin was 15 amino acids long and differed from rat scotophobin by one amino acid. The gene for goldfish scotophobin must differ from that of rat scotophobin by:
A codon, which codes for a single amino acid in the final protein, consists of three nucleotides. At least one nucleotide must be changed to code for a different amino acid. Note that changing three nucleotides can also lead to a change in a single amino acid, but only if these nucleotides are in the same codon.Choice A is incorrect because the gene consists of DNA, not amino acids.Choice B is incorrect because a change in three codons will lead to a change in three amino acids, not one.Choice D is incorrect because a change in a single nucleotide can cause a codon to code for a different amino acid.
In 1972, Georges Ungar reported the discovery of a peptide that appeared to transfer learning. Ungar's claim was based on experiments in which rats placed in a chamber with specially designed dark and light regions were trained to avoid the dark regions of the chamber. Following their training, the rats were killed and brain extracts were prepared. These brain extracts were injected into naive rats which were then observed to acquire the fear of darkness without training. Two hypotheses were proposed to explain these remarkable results:Hypothesis 1Ungar concluded that the extracts contained some chemical that transmitted the learned fear of darkness to the naive rats. A fifteen amino-acid polypeptide was isolated from the brain extracts and sequenced. Ungar claimed that this peptide, called scotophobin, was a chemical transmitter of learning. The peptide had the primary structure shown below:C-ser-asp-asn-arg-gln-gln-gly-lys-ser-ala-arg-gln-glygly-tyr-NScotophobinHypothesis 2Other researchers, who tested scotophobin but could not reproduce Ungar's results, argued that scotophobin did not transfer the learned fear of darkness. Instead, they suggested that scotophobin, which is structurally similar to ACTH and vasopressin, acted to increase stress in the rats. Since stress increases sympathetic nervous activity, rats injected with scotophobin would become hyperactive and tend to spend less time in the dark regions of the experimental chamber. They argued that such stress responses in the rats could be misinterpreted as a fear of darkness. Ungar's claim was further weakened by chemical analysis in which both the scotophobin extracts which Ungar had injected into the naive rats and a sample of synthesized scotophobin peptide were subjected to SDS polyacrylamide gel electrophoresis, as shown in Figure 1. Figure 1Researchers were interested in purifying a second protein (protein X) from Ungar's extract. The gene segment encoding protein X was believed to consist of thirty nucleotides. According to Figure 1, which band could represent protein X?
If the amino acid sequence encoding for Protein X is thirty nucleotides long, then Protein X consists of 10 amino acids. Protein X is thus smaller than scotophobin. The technique of electrophoresis uses an electrical field to separate proteins based on size. Larger proteins subjected to the same electric field will move more slowly than smaller proteins. Band C on Figure 1 which is common to the extract and to the purified protein represents scotophobin. Bands A and B which are closer to the top of the gel would represent proteins larger than scotophobin. Band D, which is below band C, represents a protein that has migrated further and is thus smaller than scotophobin. Of the choices, only band D could potentially represent Protein X.Choices A and B are incorrect because bands A and B, which have migrated less than band C, represent proteins that are larger than scotophobin.Choice C is incorrect because band C is common to both the extract and the purified protein, and must therefore represent scotophobin itself.
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