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03 Oct 2020, 13:17
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GMATNinja VeritasKarishma ChiranjeevSingh
Snyder et al. propose that caffeine, which is structurally similar to adenosine, is able to bind to both types of receptors, which prevents adenosine from attaching there and allows the neurons to fire more readily than they otherwise would
can you please explain here which refers to either receptor or caffeine.
according to meaning it should refer to caffeine but according to grammer rule it refers to receptors.
if it refers to caffeine how it can refer to very far away noun please give your insights
Snyder et al. propose that caffeine, which is structurally similar to adenosine, is able to bind to both types of receptors, which prevents adenosine from attaching there and allows the neurons to fire more readily than they otherwise would
can you please explain here which refers to either receptor or caffeine.
according to meaning it should refer to caffeine but according to grammer rule it refers to receptors.
if it refers to caffeine how it can refer to very far away noun please give your insights
palaknayyar
16 May 2021, 01:12
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Quote:
Part of New RC Series- Please check this link for more questions
Caffeine, the stimulant in coffee, has been called “the most widely used psychoactive substance on Earth.” Snyder, Daly, and Bruns have recently proposed that caffeine affects behavior by countering the activity in the human brain of a naturally occurring chemical called adenosine. Adenosine normally depresses neuron firing in many areas of the brain. It apparently does this by inhibiting the release of neurotransmitters, chemicals that carry nerve impulses from one neuron to the next.
Like many other agents that affect neuron firing, adenosine must first bind to specific receptors on neuronal membranes. There are at least two classes of these receptors, which have been designated A1 and A2. Snyder et al. propose that caffeine, which is structurally similar to adenosine, is able to bind to both types of receptors, which prevents adenosine from attaching there and allows the neurons to fire more readily than they otherwise would.
For many years, caffeine’s effects have been attributed to its inhibition of the production of phosphodiesterase, an enzyme that breaks down the chemical called cyclic AMP. A number of neurotransmitters exert their effects by first increasing cyclic AMP concentrations in target neurons. Therefore, prolonged periods at the elevated concentrations, as might be brought about by a phosphodiesterase inhibitor, could lead to a greater amount of neuron firing and, consequently, to behavioral stimulation. But Snyder et al. point out that the caffeine concentrations needed to inhibit the production of phosphodiesterase in the brain are much higher than those that produce stimulation. Moreover, other compounds that block phosphodiesterase’s activity are not stimulants.
To buttress their case that caffeine acts instead by preventing adenosine binding, Snyder et al. compared the stimulatory effects of a series of caffeine derivatives with their ability to dislodge adenosine from its receptors in the brains of mice. “In general,” they reported, “the ability of the compounds to compete at the receptors correlates with their ability to stimulate locomotion in the mouse; i.e., the higher their capacity to bind at the receptors, the higher their ability to stimulate locomotion.” Theophylline, a close structural relative of caffeine and the major stimulant in tea, was one of the most effective compounds in both regards.
There were some apparent exceptions to the general correlation observed between adenosine receptor binding and stimulation. One of these was a compound called 3-isobutyl-1-methylxanthine (IBMX), which bound very well but actually depressed mouse locomotion. Snyder et al. suggest that this is not a major stumbling block to their hypothesis. The problem is that the compound has mixed effects in the brain, a not unusual occurrence with psychoactive drugs. Even caffeine, which is generally known only for its stimulatory effects, displays this property, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.
Like many other agents that affect neuron firing, adenosine must first bind to specific receptors on neuronal membranes. There are at least two classes of these receptors, which have been designated A1 and A2. Snyder et al. propose that caffeine, which is structurally similar to adenosine, is able to bind to both types of receptors, which prevents adenosine from attaching there and allows the neurons to fire more readily than they otherwise would.
For many years, caffeine’s effects have been attributed to its inhibition of the production of phosphodiesterase, an enzyme that breaks down the chemical called cyclic AMP. A number of neurotransmitters exert their effects by first increasing cyclic AMP concentrations in target neurons. Therefore, prolonged periods at the elevated concentrations, as might be brought about by a phosphodiesterase inhibitor, could lead to a greater amount of neuron firing and, consequently, to behavioral stimulation. But Snyder et al. point out that the caffeine concentrations needed to inhibit the production of phosphodiesterase in the brain are much higher than those that produce stimulation. Moreover, other compounds that block phosphodiesterase’s activity are not stimulants.
To buttress their case that caffeine acts instead by preventing adenosine binding, Snyder et al. compared the stimulatory effects of a series of caffeine derivatives with their ability to dislodge adenosine from its receptors in the brains of mice. “In general,” they reported, “the ability of the compounds to compete at the receptors correlates with their ability to stimulate locomotion in the mouse; i.e., the higher their capacity to bind at the receptors, the higher their ability to stimulate locomotion.” Theophylline, a close structural relative of caffeine and the major stimulant in tea, was one of the most effective compounds in both regards.
There were some apparent exceptions to the general correlation observed between adenosine receptor binding and stimulation. One of these was a compound called 3-isobutyl-1-methylxanthine (IBMX), which bound very well but actually depressed mouse locomotion. Snyder et al. suggest that this is not a major stumbling block to their hypothesis. The problem is that the compound has mixed effects in the brain, a not unusual occurrence with psychoactive drugs. Even caffeine, which is generally known only for its stimulatory effects, displays this property, depressing mouse locomotion at very low concentrations and stimulating it at higher ones.
D
71. A. The passage discusses a current investigation, not one planned for the future.
B. The passage examines two explanations, but the earlier theory is discussed only to expose its weakness and the diff erences between the explanations are not reconciled. Most of the passage is devoted to the more recent hypothesis.
C. Only two theories are presented in the passage.
D. Correct. Th e recent hypothesis provides an alternative to an earlier one and is supported by evidence and arguments.
E. Lines 32–37 do pose such a challenge to the earlier theory; however, the challenge is a small part of the whole passage. Similarly, in the final paragraph, an exception to the more recent theory is introduced, only to be dismissed as an unimportant concern.
The correct answer is D.
B. The passage examines two explanations, but the earlier theory is discussed only to expose its weakness and the diff erences between the explanations are not reconciled. Most of the passage is devoted to the more recent hypothesis.
C. Only two theories are presented in the passage.
D. Correct. Th e recent hypothesis provides an alternative to an earlier one and is supported by evidence and arguments.
E. Lines 32–37 do pose such a challenge to the earlier theory; however, the challenge is a small part of the whole passage. Similarly, in the final paragraph, an exception to the more recent theory is introduced, only to be dismissed as an unimportant concern.
The correct answer is D.
1. The primary purpose of the passage is to
(A) discuss a plan for investigation of a phenomenon that is not yet fully understood
(B) present two explanations of a phenomenon and reconcile the differences between them
(C) summarize two theories and suggest a third theory that overcomes the problems encountered in the first two
(D) describe an alternative hypothesis and provide evidence and arguments that support it
(E) challenge the validity of a theory by exposing the inconsistencies and contradictions in it
D
72. A. The passage does not suggest that adenosine stimulates behavior.
B. While the final paragraph reveals that caffeine displays mixed eff ects, the passage does not state that adenosine has a stimulatory effect.
C. Increasing cyclic AMP concentrations is part of the earlier theory, not that of Snyder et al.
D. Correct. Lines 17–21 explain that caffeine binds to the receptors, releasing neurotransmitters, whereas adenosine hinders that release.
E. Inhibiting the production of phosphodiesterase is discussed in the earlier theory, not in the work of Snyder et al.
The correct answer is D.
B. While the final paragraph reveals that caffeine displays mixed eff ects, the passage does not state that adenosine has a stimulatory effect.
C. Increasing cyclic AMP concentrations is part of the earlier theory, not that of Snyder et al.
D. Correct. Lines 17–21 explain that caffeine binds to the receptors, releasing neurotransmitters, whereas adenosine hinders that release.
E. Inhibiting the production of phosphodiesterase is discussed in the earlier theory, not in the work of Snyder et al.
The correct answer is D.
(A) stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans only
(B) has mixed effects in the brain, whereas adenosine has only a stimulatory effect
(C) increases cyclic AMP concentrations in target neurons, whereas adenosine decreases such concentrations
(D) permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits such release
(E) inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration in the brain, whereas adenosine inhibits only neuron firing
A
73. A. Correct. The results of one experiment can be explained by mixed eff ects in the brain, which Snyder et al. say may occur with psychoactive drugs.
B. This response refers back to the earlier theory, not to Snyder et al.’s response concerning IBMX experiment results.
C. Caffeine is only included within the broad category of psychoactive drugs.
D. This effect is attributed to one compound,IBMX, not to all psychoactive drugs.
E. This ability is not discussed in the passage.
The correct answer is A.
B. This response refers back to the earlier theory, not to Snyder et al.’s response concerning IBMX experiment results.
C. Caffeine is only included within the broad category of psychoactive drugs.
D. This effect is attributed to one compound,IBMX, not to all psychoactive drugs.
E. This ability is not discussed in the passage.
The correct answer is A.
(A) mixed effects in the brain
(B) inhibitory effects on enzymes in the brain
(C) close structural relationships with caffeine
(D) depressive effects on mouse locomotion
(E) the ability to dislodge caffeine from receptors in the brain
E
74. A. Lines 54–55 state that IBMX binds to receptors.
B. Lines 17–19 state that caff eine binds to receptors.
C. Lines 13–14 state that adenosine binds to receptors.
D. Lines 46–50 state that theophylline binds to receptors.
E. Correct. The passage includes no evidence that phosphodiesterase binds to receptors.
The correct answer is E.
B. Lines 17–19 state that caff eine binds to receptors.
C. Lines 13–14 state that adenosine binds to receptors.
D. Lines 46–50 state that theophylline binds to receptors.
E. Correct. The passage includes no evidence that phosphodiesterase binds to receptors.
The correct answer is E.
(A) IBMX
(B) caffeine
(C) adenosine
(D) theophylline
(E) phosphodiesterase
B
75. A. Phosphodiesterase is discussed in an entirely diff erent context in lines 22–25.
B. Correct. Lines 17–19 suggest that caffeine’s structural similarity to adenosine may be responsible for its ability to bind to A1 and A2 receptors.
C. Caff eine acts on neurotransmitters; it is not structurally similar to them.
D. Caffeine’s ability to stimulate behavior results from, rather than causes, this process.
E. The passage does not discuss the natural occurrence of these compounds.
The correct answer is B.
B. Correct. Lines 17–19 suggest that caffeine’s structural similarity to adenosine may be responsible for its ability to bind to A1 and A2 receptors.
C. Caff eine acts on neurotransmitters; it is not structurally similar to them.
D. Caffeine’s ability to stimulate behavior results from, rather than causes, this process.
E. The passage does not discuss the natural occurrence of these compounds.
The correct answer is B.
(A) The chemical relationship between caffeine and phosphodiesterase
(B) The structural relationship between caffeine and adenosine
(C) The structural similarity between caffeine and neurotransmitters
(D) The ability of caffeine to stimulate behavior
(E) The natural occurrence of caffeine and adenosine in the brain
B
76. A. The quotation explains results of an experiment, not assumptions about a theory.
B. Correct. The quotation summarizes the experiment with mice and reports a major finding in support of the hypothesis.
C. The quotation generalizes on the basis of the experiment; it does not limit the finding to mice.
D. Specific, not general, correlations were made between the ability to bind to receptors and to stimulate locomotion.
E. The passage includes no such objections; therefore no refutations are needed.
The correct answer is B.
B. Correct. The quotation summarizes the experiment with mice and reports a major finding in support of the hypothesis.
C. The quotation generalizes on the basis of the experiment; it does not limit the finding to mice.
D. Specific, not general, correlations were made between the ability to bind to receptors and to stimulate locomotion.
E. The passage includes no such objections; therefore no refutations are needed.
The correct answer is B.
(A) reveal some of the assumptions underlying their theory
(B) summarize a major finding of their experiments
(C) point out that their experiments were limited to the mouse
(D) indicate that their experiments resulted only in general correlations
(E) refute the objections made by supporters of the older theory
Does this question only have 6 questions? I remember seeing this in an OG and recall 8 or 9 questions.. can someone confirm please?
