Nitric oxide, NO, has recently been found to have widespread physiological effects, acting as a major regulator in the nervous, cardiovascular, and immune systems. The production of NO in the body is regulated by specific NOS enzymes which exist in at least three different isoforms bNOS, eNOS, and macNOS. Each of these isoforms differ in location and function and serve to mediate different physiological responses to NO. Some physiological roles of NO have been demonstrated as follows:I). In the central nervous system, NO production is regulated by bNOS. Calcium ion concentrations of 200-400 nM in the central nervous system activate bNOS to catalyze the formation of NO. NO exerts definite effects on brain function although its specific roles are not well established. bNOS inhibitors have been found to block the release of neurotransmitter from presynaptic neurons. Excess levels of NO are also thought to contribute to neurodegenerative disorders such as Alzheimer's disease.II). In the blood vessels, NO is produced by eNOS which is activated by Ca2+ concentrations of 200-400 nM. NO acts as the major endogenous vasodilator in blood vessels. It diffuses into smooth muscle cells and leads to muscle relaxation by stimulating cGMP formation through activation of guanylyl cyclase. In addition, NO regulates the vascular system by inhibiting platelet aggregation and adhesion.III). The role of NO in the immune system is regulated by macNOS through a pathway that is not Ca2+ dependent. Rather, exposure to cytokines, including interleukin-1 and interferon- , leads to synthesis of large amounts of NO by activation of macNOS in response to inflammatory stimulI). The NO produced plays a definitive role in the mediation of the activities of macrophages and neutrophils. NO also acts to inhibit the mechanism of viral replication.A patient has accidentally ingested a toxin which acts as an eNOS inhibitor. According to the passage, the effects of this toxin would most likely include:
Answer(s): D
eNOS produces NO in endothelial tissue, leading to vasodilation. This would tend to decrease blood pressure.An eNOS inhibitor would thus block production of NO, decreasing vasodilation and thereby increasing blood pressure.Choice A is incorrect because an eNOS inhibitor would produce an increase in blood pressure.Choice B is incorrect because a macNOS regulates the production of NO in the immune system. Also, inhibiting NO production would not increase immune response which is positively linked to NO concentration.Choice C is incorrect because increased blood pressure would tend to increase urine production.
Nitric oxide, NO, has recently been found to have widespread physiological effects, acting as a major regulator in the nervous, cardiovascular, and immune systems. The production of NO in the body is regulated by specific NOS enzymes which exist in at least three different isoforms bNOS, eNOS, and macNOS. Each of these isoforms differ in location and function and serve to mediate different physiological responses to NO. Some physiological roles of NO have been demonstrated as follows:I). In the central nervous system, NO production is regulated by bNOS. Calcium ion concentrations of 200-400 nM in the central nervous system activate bNOS to catalyze the formation of NO. NO exerts definite effects on brain function although its specific roles are not well established. bNOS inhibitors have been found to block the release of neurotransmitter from presynaptic neurons. Excess levels of NO are also thought to contribute to neurodegenerative disorders such as Alzheimer's disease.II). In the blood vessels, NO is produced by eNOS which is activated by Ca2+ concentrations of 200-400 nM. NO acts as the major endogenous vasodilator in blood vessels. It diffuses into smooth muscle cells and leads to muscle relaxation by stimulating cGMP formation through activation of guanylyl cyclase. In addition, NO regulates the vascular system by inhibiting platelet aggregation and adhesion.III). The role of NO in the immune system is regulated by macNOS through a pathway that is not Ca2+ dependent. Rather, exposure to cytokines, including interleukin-1 and interferon- , leads to synthesis of large amounts of NO by activation of macNOS in response to inflammatory stimulI). The NO produced plays a definitive role in the mediation of the activities of macrophages and neutrophils. NO also acts to inhibit the mechanism of viral replication.A patient with hypertension (high blood pressure) is treated with nitroglycerin, which spontaneously breaks down to give NO. This treatment will be:
Answer(s): B
The passage states that in blood vessels, NO acts as a major vasodilator. Thus, NO could be used to alleviate high blood pressure. Nitroglycerin, as stated in the question stem, breaks down spontaneously (i.e., without requiring catalyzation by an NOS enzyme). Thus, by administering nitroglycerin, NO will be generated (without eNOS) in the patient's body and its presence will lead to vasodilation, causing a drop in blood pressure and relieving the hypertension.Choice A is incorrect because NO will not activate eNOS. eNOS is activated by Ca2+ and functions normally to produce NO.Choice C is incorrect because NO will be spontaneously generated from the nitroglycerin without requiring catalyzation by eNOS. Thus, although eNOS will not be activated, the NO generated from the administered nitroglycerin will dilate the blood vessels and relieve hypertension.Choice D is incorrect because NO is very unstable and will not tend to build up. It is also not likely that NO would be capable of crossing the blood/brain barrier and affecting the nervous system.
Nitric oxide, NO, has recently been found to have widespread physiological effects, acting as a major regulator in the nervous, cardiovascular, and immune systems. The production of NO in the body is regulated by specific NOS enzymes which exist in at least three different isoforms bNOS, eNOS, and macNOS. Each of these isoforms differ in location and function and serve to mediate different physiological responses to NO. Some physiological roles of NO have been demonstrated as follows:I). In the central nervous system, NO production is regulated by bNOS. Calcium ion concentrations of 200-400 nM in the central nervous system activate bNOS to catalyze the formation of NO. NO exerts definite effects on brain function although its specific roles are not well established. bNOS inhibitors have been found to block the release of neurotransmitter from presynaptic neurons. Excess levels of NO are also thought to contribute to neurodegenerative disorders such as Alzheimer's disease.II). In the blood vessels, NO is produced by eNOS which is activated by Ca2+ concentrations of 200-400 nM. NO acts as the major endogenous vasodilator in blood vessels. It diffuses into smooth muscle cells and leads to muscle relaxation by stimulating cGMP formation through activation of guanylyl cyclase. In addition, NO regulates the vascular system by inhibiting platelet aggregation and adhesion.III). The role of NO in the immune system is regulated by macNOS through a pathway that is not Ca2+ dependent. Rather, exposure to cytokines, including interleukin-1 and interferon- , leads to synthesis of large amounts of NO by activation of macNOS in response to inflammatory stimulI). The NO produced plays a definitive role in the mediation of the activities of macrophages and neutrophils. NO also acts to inhibit the mechanism of viral replication.According to the passage, NO may counter viral infection by all of the following mechanisms EXCEPT:
Answer(s): C
The passage indicates that NO inhibits viral replication and mediates the activities of macrophages. It does not mention the denaturing of viral protein coats as an activity of NO.Choice A is incorrect because macrophages are white blood cells which engulf and destroy foreign agents and their activity is mediated by NO.Choice B is incorrect because NO inhibits viral replication and may do so by inhibiting the synthesis of viral RNA.Choice D is incorrect because NO may inhibit viral replication by inhibiting viral release from infected cells.
Synthetic dyes constitute a commercially significant area of organic chemistry. The color producing properties of these compounds are the result of highly delocalized electron systems giving rise to electronic transitions whose absorptions occur in the visible region. Most commercially useful dyes can be classified as one of three types anthraquinones, azo dyes, or triarylmethyl salts. Examples of each type are illustrated in Figure 1.Figure 1In order for a dye to be useful in the fabric industry, it must have sufficient affinity for the polymeric fibers of which the material is composed; the dye must not only impart a color to the fabric, but must also do so in a relatively permanent manner (color fastness). Proper design of synthetic polymers requires the placement of acidic or basic side chains along the polymer backbone such that binding sites are available for dying. Similarly, dyes must be produced not only with the appropriate color-producing structure, but also with an affinity for the fabric in question. The structural units of several common synthetic fibers are shown in Figure 2.Figure 2Certain natural protein fibers such as silk or wool can be treated with aqueous base, then with solutions containing cationic dyes such as malachite green to produce color fast yarns. The most likely explanation for the affinity of malachite green for silk or wool via this process is that:
Answer(s): A
Since malachite green, as depicted in figure 1, is cationic, it follows that it will have an affinity for anionic binding sites. Such anionic binding sites, alluded to in the passage, would be produced from acidic side chains upon treatment with aqueous base, and acidic side chains in natural proteins would most likely contain the COOH functionality.Choice B is incorrect since acidic side chains on natural amino acids often contain OH groups.Choice C is wrong since treatment with base is part of the process of producing color-fast yarns; this treatment makes the color stick, it does not break down the yarn into smaller polypeptide chains as choice C suggests.Choice D is incorrect because the base reacts with the fiber before the dye is added, and not with the dye.
Synthetic dyes constitute a commercially significant area of organic chemistry. The color producing properties of these compounds are the result of highly delocalized electron systems giving rise to electronic transitions whose absorptions occur in the visible region. Most commercially useful dyes can be classified as one of three types anthraquinones, azo dyes, or triarylmethyl salts. Examples of each type are illustrated in Figure 1.Figure 1In order for a dye to be useful in the fabric industry, it must have sufficient affinity for the polymeric fibers of which the material is composed; the dye must not only impart a color to the fabric, but must also do so in a relatively permanent manner (color fastness). Proper design of synthetic polymers requires the placement of acidic or basic side chains along the polymer backbone such that binding sites are available for dying. Similarly, dyes must be produced not only with the appropriate color-producing structure, but also with an affinity for the fabric in question. The structural units of several common synthetic fibers are shown in Figure 2. Figure 2Dacron belongs to which of the following general classifications?
Dacron, as shown in figure 2, is a polyester since it contains the COOR functionality in its monomer (subunit).Choice A is incorrect since polyamides would need to contain nitrogen in their monomers in order to contain an amide functional group, CONR2. Dacron does not. (However, nylon, also shown in figure 2, is a polyamide.) Choice C is wrong, like A, for lack of nitrogen, a necessary element to classify the monomeric compound as a urethane, ArNHCOOR.Choice D is wrong since the monomer structure is not a peptide.
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