OG12-16 即 OG11-15 (生物题材)文章结构分析 - 食物对血清素的影响

lisalee

这是我在OG-RC上首次碰到的生物科学题材的文章, 难就难在:
1) 原文专业术语多, 指代及相互关系比较复杂;
2) 题目多为细节题, 涉及的点在原文反复出现, 不便定位;
4min读完原文, 一头雾水啊~平均2min做一道题, 9个还是错了5个...
所以我只好认真仔细, 不计时间的把原文又读了一遍, 总算大致理解了其中的关系和文章结构,
把文章理解透了, 细节题和推断题就可以迎刃而解了
在此跟同学们分享一下, 希望能对此题迷茫的战友们提供一个比较清晰的思路~
备注: 黄色高亮是主题句定位, 灰色高亮是细节题定位, 蓝色高亮是推断题定位,蓝色字体是逻辑题定位
先将原文帖一个~ It was once believed that the brain was
independent of metabolic processes occurring
elsewhere in the body. In recent studies, however,
we have discovered that the production and release
(5)in brain neurons of the neurotransmitter serotonin
(neurotransmitters are compounds that neurons use
to transmit signals to other cells) depend directly on
the food that the body processes.
Our first studies sought to determine whether
(10) the increase in serotonin observed in rats given
a large injection of the amino acid tryptophan
might also occur after rats ate meals that change
tryptophan levels in the blood. We found that,
immediately after the rats began to eat, parallel
(15) elevations occurred in blood tryptophan, brain
tryptophan, and brain serotonin levels. These
findings suggested that the production and release
of serotonin in brain neurons were normally coupled
with blood-tryptophan increases. In later studies we
(20) found that injecting insulin into a rat's bloodstream
also caused parallel elevations in blood and brain
tryptophan levels and in serotonin levels.We then
decided to see whether the secretion of the animal's
own insulin similarly affected serotonin production.
(25) We gave the rats a carbohydrate-containing meal
that we knew would elicit insulin secretion. As we
had hypothesized, the blood tryptophan level and
the concentrations of tryptophan and of serotonin
in the brain increased after the meal.
(30)Surprisingly, however, when we added a large
amount of protein to the meal, brain tryptophan
and serotonin levels fell. Since protein contains
tryptophan, why should it depress brain tryptophan
levels? The answer lies in the mechanism that
(35) provides blood tryptophan to the brain cells. This
same mechanism also provides the brain cells with
other amino acids found in protein, such as tyrosine
and leucine. The consumption of protein increases
blood concentration of the other amino acids much
(40) more, proportionately, than it does that of tryptophan.
The more protein is in a meal, the lower is the ratio
of the resulting blood-tryptophan concentration to
the concentration of competing amino acids, and
the more slowly is tryptophan provided to the brain.
(45) Thus the more protein in a meal, the less serotonin
subsequently produced and released.

lisalee

全文分为三段:
第一段引出主题句, 说明全文的主旨:摄入食物对血清素的产生和释放的影响
第二段引用一些研究结果来验证上述研究发现, 其中包括3个试验:
    1) 注入amino acid tryptophan 并让小鼠进食, 可以使blood tryptophan, brain tryptophan, and brain serotonin 水平上升;
    2) 注入insulin, 也可以获得上述结果;
    3) 给予可以诱导小鼠自行产生insulin的食物, 也可以获得上述结果;
第三段提出一个与假设相悖的试验现象, 增加protein摄入反而会导致 brain tryptophan and serotonin 水平下降;
进而对此现象进行解释, 这是因为:
protein包括blood typtophan和其他amino acid trptophan (比如 tyrosine 和 leucine) ,二者都有向脑细胞提供blood tryptophan的机制, 但是消耗protein的比例不同, 后者消耗较大使得brain tryptophan的供应变慢, 进而影响到brain serotonin的产生和释放相对较少.