[求助]请问各位G友,那篇咖啡因的分析在哪?明天就考试了,急,谢谢大家

millermrtt

[求助]请问各位G友,那篇咖啡因的分析在哪?明天就考试了,急,谢谢大家

nedelon

结论解释

describe an alternative hypothesis and provide evidence and arguments that support it

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 brain of 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（permits release of neurotransmitters when it is bound to adenosine receptors，whereas adenosine inhibits such release），chemicals that carry nerve impulses from one neuron to the next．

1. 引出要介绍的对象 2。Caffeine如何stimulate 3。无 4。Snyder, daly, Bruns; Caffeine affect by couter ade (barin chemical); ade à inhibit release of neurotransmitters to depress neuron firing 5。引出对象，等待下文解释

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 a1．propose that caffeine，which is structurally similar to adenosine，is able to bind to both types of receptors】（Snyder et al suggest that caffeine’s ability to bind to A1 and A2 receptors can be at least partially attributed to The structural relationship between caffeine and adenosine），which prevents adenosine from attaching there and allows the neurons to fire more readily than they otherwise would．
            

1．cafeine如何stimulate 2.caffeine具体的做法 3。无 4。Caffeine bind A1&A2 (avoid ade to bind them) à neurons fire more 5. 上文的解释

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（phosphodiesterase is unable to bind to specific receptors in the brain）. A number of neurotransmitters exert their effects by first increasing cyclic AM P 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 aI 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．
            

1．介绍以前的一种看法 2。以前认为caffeine是阻挡phospho 3。－ 4。BUT, concentration to inhibit > to produce stimulation; other compounds to block phosph not stimulate 5.提出一种不同看法，但是被反驳

 

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（the passage quoted Snyder here in order to summarize a major finding of their experiment） i. e., the higher their capacity to bind at the receptors，the higher their ability to stimulate locomotion．"Theophylline，a close structural relative of the most effective compounds in both regards．

1．举例来证明 2。做的试验证明synder的说法正确 3。＋ 4。Compared a series of caffeine derivatives; The higher capacity to bind receptors, the higher to stimulate locomotion; theoph most 5.例证第一段论点

 

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（In response to experimental results concerning IBMX，Snyder et a l contended that it is not uncommon for psychoactive drugs to have mixed effects in the brain）．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。

1．介绍一些不符合的 2。尽管理论大方向对，总是有特殊情况 3。小－ 4。IBMXàbound and depress; snyder suggest à mixed effects, not unusaual 5.举出反例，但是不ruin全文论点。
Questions 64-69 refer to the passage a hove．

64．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

 

65. According to Snyder et al, caffeine differs from adenosine in that caffeine

(A)  stimulates behavior in the mice 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

66． In response to experimental results concerning IBMX，Snyder et a l contended that it is not uncommon for psychoactive drugs to have

(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

67． According to Snyder et al，all of the following compounds can bind to specific receptors in the brain EXCEPT

(A)  IBMX

(B)  caffeine

(C)  adenosine

(D)  theophylline

(E)  phosphodiesterase

68. Snyder et al suggest that caffeine’s ability to bind to A1 and A2 receptors can be at least partially attributed to表示有可能因为 which of the following?

(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

69. The author quotes Snyder et al. in lines 43—48 most probably in order to

(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 mice

(D)  indicate that their experiments resulted only in genera l correlations

(E)  refute the objections made by supporters of the older theory