GMAT OG第一篇分析示例.doc

Caffeine, the stimulant in coffee, has been called “the most widely used psychoactive substance on Earth .” Synder, Daly and Bruns have recently proposed that caffeine affects behavior by countering the activity in (5) 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. (10) 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 struc- (15) turally 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. 读完第一段，要回头来回顾一下，本段讲了些什么内容？ 根据刚才我们的分析，可以很容易的用两秒钟在脑子里过一遍第一段的逻辑简图：S人物认为Caffeine是通过counter于小A起作用的(小A的作用原理是绑定在A1A2上(S认为Caffeine在结构上与小A类似，从而代替了小A绑定而起作用。 看，这样一来，复杂的原理解释的第一段就简化成了一个简单的逻辑简图，只有三块内容。再精简一点，不难发现，其实这三句话可以合并为一句话，那就是：Caffeine是通过反作用于小A来作用的。本段要记住的是：小A和Caffeine的关系：结构类似。本段我划线的那句话，在GMAT阅读中经常能够见到类似的表达：出题的人也知道考生不是专家，因此，在给出一个专有名词的时候，一般会在后面做出解释。如果时间充裕，你可以去读一下这个解释，有助于理解文章意思。如果时间紧张，这个同位语解释的部分就不用去读了，因为它的内容一定是解释那个名词。在下面一段中，我也有一个划线句子，作用和本段的划线是一模一样的：解释专业术语。 For many years, caffeine’s effects have been attri- (20) buted to its inhibition of the production of phosphodi- esterase, an enzyme that breaks down the chemical called cyclic AMP.A number of neurotransmitters exert their effects by first increasing cyclic AMP concentra- tions in target neurons. Therefore, prolonged periods at (25) the elevated concentrations, as might be brought about by a phosphodiesterase inhibitor, could lead to a greater amount of neuron firing and, consequently, to behav- ioral stimulation. But Snyder et al point out that the caffeine concentrations needed to inhib