新SAT阅读真题二

新SAT阅读真题二
新SAT阅读真题二

新SAT阅读真题二

Exercise 2

This passage is excerpted from L.M. Montgomery, “The Gossip of Valley View,” originally published in 1910.

It was the ?rst of April, and Julius Barrett, aged fourteen, perched on his father's gatepost, watched ruefully the low descending sun, and counted that day lost. He had not succeeded in "fooling" a single person, although he had tried repeatedly. One and all, old and young, of his intended victims had been too wary for Julius. Hence, Julius was disgusted and ready for anything in the way of a stratagem or a spoil.

The Barrett gatepost topped the highest hill in Valley View. Julius could see the entire settlement, from "Young" Thomas Everett's farm, a mile to the west, to Adelia Williams's weather-grey little house on a moonrise slope to the east. He was gazing moodily down the muddy road when Dan

Chester, homeward bound from the post of?ce, came riding sloppily along on his grey mare and pulled up by the Barrett gate to hand a paper to Julius. Dan was a young man who took life and himself very seriously. He seldom smiled, never joked, and had a Washingtonian reputation for veracity. Dan had never told a conscious falsehood in his life; he never even exaggerated.

Julius, beholding Dan's solemn face, was seized with a perfectly irresistible desire to "fool" him. At the same moment his eye caught the dazzling re?ection of the setting sun on the windows of Adelia Williams's house, and he had an inspiration little short of diabolical. "Have you heard the news, Dan?" he asked.

"No, what is it?" asked Dan.

"I dunno's I ought to tell it," said Julius re?ectively. "It's kind of a family affair, but then Adelia didn't say not to, and anyway it'll be all over the place soon. So I'll tell you, Dan, if you'll promise never to tell who told you. Adelia Williams and Young Thomas Everett are going to be married."Julius delivered himself of this tremendous lie with a transparently earnest countenance. Yet Dan, credulous as he was, could not believe it all at once."Git out," he said.

"It's true, 'pon my word," protested Julius. "Adelia was up last night and told Ma all about it. Ma's her cousin, you know. The wedding is to be in June, and Adelia asked Ma to help her get her quilts and things ready."

Julius reeled all this off so glibly that Dan ?nally believed the story, despite the fact that the people thus coupled together in prospective matrimony were the very last people in Valley View who could have been expected to marry each other. Young Thomas was a con?rmed bachelor of ?fty, and Adelia Williams was forty; they were not supposed to be even well acquainted, as the Everetts and the Williamses had never been very friendly, although no open feud existed between them.

Nevertheless, in view of Julius's circumstantial statements, the amazing news must be true, and Dan was instantly agog to carry it further. Julius watched Dan and the grey mare out of sight, fairly writhing with ecstasy. Oh, but Dan had been easy! The story would be all over Valley View in twenty-four hours. Julius laughed until he came near to falling off the gatepost.

At this point Julius and Danny drop out of our story, and Young Thomas enters.

It was two days later when Young Thomas heard that he was to be married to Adelia Williams in June. Eben Clark, the blacksmith, told him when he went to the forge to get his horse shod. Young Thomas laughed his big jolly laugh. Valley View gossip had been marrying him off for the last thirty years, although never before to Adelia Williams."It's news to me," he said tolerantly.

Eben grinned broadly. "Ah, you can't bluff it off like that, Tom," he said. "The news came too straight this time. Well, I was glad to hear it, although I was mighty surprised. I never thought of you and Adelia. But she's a ?ne little woman and will make you a capital wife."

Young Thomas grunted and drove away. He had a good deal of business to do that day, involving calls at various places—the store for molasses, the mill for ?our, Jim Bentley's for seed grain, the doctor's for toothache drops for his housekeeper, the post of?ce for mail—and at each and every place he was joked about his approaching marriage. In the end it rather annoyed Young Thomas. He drove home at last in what was for him something of a temper. How on earth had that fool story started? With such detailed circumstantiality of rugs and quilts, too? Adelia Williams must be going to marry somebody, and the Valley View gossips, unable to locate the man, had guessed Young Thomas.

Over the course of the passage, the main focus shifts from

A a character’s attempt at a practical joke to the effect felt by another character.

B a depiction of a small town to the relationships among the characters in the town.

C a character’s humorous behavior to the evolution of a story passed around the town.

D a description of a friendship to a discussion of a prank perpetuated by the town.

QUESTION 2 OF 11

Which statement best characterizes the relationship between Julius and Dan?

A Dan is trusting of Julius and does not question his story about Thomas.

B Dan is skeptical by nature but trusts Julius to always tell him the truth.

C Dan's disposition makes him an attractive target for Julius' plan.

D Dan’s attitude towards Julius illustrates an imbalanced friendship. QUESTION 3 OF 11

As used in line 2 (“ruefully”) , the phrase “ruefully” most nearly means

A mournfully.

B apologetically.

C repentantly.

D angrily.

QUESTION 4 OF 11

As used in line 18 (“veracity.”), “veracity” most nearly means

A candor.

B truthfulness.

C verisimilitude.

D impartiality.

QUESTION 5 OF 11

The conversation between Julius and Dan serves mainly to

A show how bored Julius is with the inhabitants of Valley View.

B provide a context for the relationships in the community.

C demonstrate Dan’s gullibility when it comes to rumors.

D establish why Julius’ story was so widely accepted.

QUESTION 6 OF 11

Which choice provides the best evidence for the answer to the previous question?

A lines 3–5 (“He . . . repeatedly”)(“He had not succeeded in "fooling" a single person, although he had tried repeatedly.”)

B lines 33–34 (“Julius . . . countenance”)(“Julius delivered himself of this tremendous lie with a transparently earnest countenance.”)

C lines 45–49 (“Young Thomas . . . them”)(“Young Thomas was a con?rmed bachelor of ?fty, and Adelia Williams was forty; they were not supposed to be even well acquainted, as the Everetts and the Williamses had never been very friendly, although no open feud existed between them.”)

D lines 50–52 (“Nevertheless . . . further”)(“Nevertheless, in view of Julius's circumstantial statements, the amazing news must be true, and Dan was instantly agog to carry it further.”)

QUESTION 7 OF 11

In the passage, Dan is characterized as someone who is

A honest.

B foolish.

C stubborn.

D distrustful.

QUESTION 8 OF 11

Which choice provides the best evidence for the answer to the previous question?

A lines 16–20 (“Dan . . . exaggerated”)(“Dan was a young man who took life and himself very seriously. He seldom smiled, never joked, and had a Washingtonian reputation for veracity. Dan had never told a conscious falsehood in his life; he never even exaggerated.”)

B lines 21–22 (“Julius . . . him”)(“Julius, beholding Dan's solemn face, was seized with a perfectly irresistible desire to "fool" him.”)

C lines 34–35 (“Yet . . . once”)(“Yet Dan, credulous as he was, could not believe it all at once.”)

D lines 53–54 (“Oh . . . easy”)(“Oh, but Dan had been easy!”) QUESTION 9 OF 11

lines 57–58 (“At . . .enters”) (“At this point Julius and Danny drop out of our story, and Young Thomas enters.”) serves mainly to

A introduce a new character and setting to the story.

B show the resulting impact of the rumor Julius started.

C add a surprising twist to the story.

D create a sense of suspense for the outcome of the prank.

QUESTION 10 OF 11

Eben’s comments in lines 66–70 (“Ah . . . wife”) (“"Ah, you can't bluff it off like that, Tom," he said. "The news came too straight this time. Well, I was glad to hear it, although I was mighty surprised. I never thought of you and Adelia. But she's a ?ne little woman and will make you a capital wife.””) primarily indicate that he A disagrees strongly with Thomas. B ?nds the rumor to be funny. C believes that Thomas is lying.

D feels unsurprised by the match.

QUESTION 11 OF 11

It can be inferred that Tom is "in something of a temper" because he

A feels exasperated by Julius’ tendency to gossip.

B believes Adelia doesn’t want to marry him.

C is agitated that he is the subject of a rumor.

D has too many errands to run in Valley View.

参考答案:ACABDDAADCC

新SAT阅读真题四

新SAT阅读真题四 Exercise 4 This passage is excerpted from Louisa May Alcott, Rose in Bloom, originally published in 1876. Three young men stood together on a wharf one bright October day awaiting the arrival of an ocean steamer with an impatience which found a vent in lively skirmishes with a small lad, who pervaded the premises like a will-o'-the-wisp and afforded much amusement to the other groups assembled there. "They are the Campbells, waiting for their cousin, who has been abroad several years with her uncle, the doctor," whispered one lady to another as the handsomest of the young men touched his hat to her as he passed, lugging the boy, whom he had just rescued from a little expedition down among the piles."Which is that?" asked the stranger. "Prince Charlie, as he's called a ?ne fellow, the most promising of the seven, but a little fast, people say," answered the ?rst speaker with a shake of the head. "Are the others his brothers?""No, cousins. The elder is Archie, a most exemplary young man. He has just gone into business with the merchant uncle and bids fair to be an honor to his family. The other, with the eyeglasses and no gloves, is Mac, the odd one, just out of college." "And the boy?" "Oh, he is Jamie, the youngest brother of Archibald, and the pet of the whole family. Mercy on us he'll be in if they don't hold on to him!"

新SAT阅读真题一

新SAT阅读真题一 如今同学们参加SAT考试,都是SAT改革之后的新SAT考试。在改革之后,SAT阅读部分也有了相应的变化。同学们要想充分的备考新SAT阅读考试,还是需要更多的来练习真题。 Exercise 1 This passage is excerpted from Jane Austen, Northanger Abbey, originally published in 1803. Mrs. Allen was so long in dressing that they did not enter the ballroom till late. As for Mr. Allen, he repaired directly to the card-room. With more care for the safety of her new gown than for the comfort of her protegee, Mrs. Allen made her way through the throng of men by the door, as swiftly as the necessary caution would allow; Catherine, however, kept close at her side, and linked her arm too ?rmly within her friend's to be torn asunder by any common effort of a struggling assembly. Still they moved on—something better was yet in view; and by a continued exertion of strength and ingenuity they found themselves at last in the passage behind the highest bench. It was a splendid sight, and she began, for the ?rst time that evening, to feel herself at a ball: she longed to dance, but she had not an acquaintance in the room. Catherine began to feel something of disappointment—she was tired of being continually pressed against by people, the generality of whose faces possessed nothing to interest, and with all of whom she was so wholly unacquainted that she could not relieve the irksomeness of

(完整版)SATog5阅读真题解析

SAT test 5 1.For a long time, most doctors maintained that taking massive doses of vitamins was relatively harmless; now, however, some are warning that excessive dosages can be _________. (A) healthy adj. 健康的 (B) expensive adj. 昂贵的 (C) wasteful adj. 浪费的 (D) toxic adj. 有毒的 (E) inane adj. 愚蠢的 解析:D,在很长的一段时间里,大多数医生认为用大量的维他命是无害的;不过现在有些人警告过量食用会----。这里however表示转折与前面的harmless是相反的意思。 2. In Jamaica Kincaid's novel Lucy, the west Indian heroine _________ her employers' world, critically examining its assumptions and values. (A) idealizes v. 理想化 (B) avoids v. 避开 (C) beautifies v. 美化 (D) scrutinizes v. 仔细检查 (E) excludes v. 排除, 解析:E,在牙买加金彩的小说露西,这个西印度群岛英雄----她的雇主的世界,精细的审视他的猜测和价值。这个句子中前后两句意思是一致的,没有转折词,所以空格所需的东西与examining是同义词,所以D。 3.The frequent name changes that the country has undergone _________ the political turbulence that has attended its recent history. (A) argue against v. 真钞,辩论 (B) contrast with v. 对比,差异 (C) testify to v. 证明 (D) jeopardize v. 危及

SAT og 5阅读真题解析

SAT test 5 1. For a long time, most doctors maintained that taking massive doses of vitamins was relatively harmless; now, however, some are warning that excessive dosages can be _________. (A) healthy adj. 健康的 (B) expensive adj. 昂贵的 (C) wasteful adj. 浪费的 (D) toxic adj. 有毒的 (E) inane adj. 愚蠢的 解析:D,在很长的一段时间里,大多数医生认为用大量的维他命是无害的;不过现在有些人警告过量食用会----。这里however表示转折与前面的harmless是相反的意思。 2. In Jamaica Kincaid's novel Lucy, the west Indian heroine _________ her employers' world, critically examining its assumptions and values. (A) idealizes v. 理想化 (B) avoids v. 避开 (C) beautifies v. 美化 (D) scrutinizes v. 仔细检查 (E) excludes v. 排除,

解析:E,在牙买加金彩的小说露西,这个西印度群岛英雄----她的雇主的世界,精细的审视他的猜测和价值。这个句子中前后两句意思是一致的,没有转折词,所以空格所需的东西与examining是同义词,所以D。 frequent name changes that the country has undergone _________ the political turbulence that has attended its recent history. (A) argue against v. 真钞,辩论 (B) contrast with v. 对比,差异 (C) testify to v. 证明 (D) jeopardize v. 危及 (E) sustain v. 支撑 解析:C,这个国家经历了频繁的国名变更---这个国家的近点史上的政治动乱。从句意可以看后句和前句是因果关系,前面证明了后面。 , clamlike bivalves of prehistoric times, were one of the most _________ forms of life on the Earth: more than 30,000 species have been _________ from fossil records. (A) plentiful adj. 丰富的...subtracted v. 减去 (B) ornate adj. 华丽的...retrieved v. 重新取回 (C) multifarious adj. 多方面的...catalogued v. 登记分类 (D) scarce adj. 缺乏的,罕见的...extracted v. 萃取的 (E) anachronistic adj. 时代错误的...extrapolated v. 推算,推断

SAT阅读测试题1

Questions 10-14 are based on the following passage. This passage is from the preface to a 1997 book by a United States journalist detailing a disagreement between doctors and family members about a child's medical treatment at a hospital in California. Under my desk I keep a large carton of cassette tapes. Though they have all been transcribed, I still like to listen to them from time to time, Some are quiet and easily understood. They are filled with the voices of American doctors, interrupted occasionally by the clink of a coffee cup or beep of a pager. The rest—more than half of them—are very noisy. They are filled with the voices of the Lees family, Hmong refugees from Laos who came to the United States in 1980. Against a background of babies crying, children playing, doors slamming, dishes clattering, a television yammering, and an air conditioner wheezing, I can hear the mother's voice, by turns breathy, nasal, gargly, or humlike as it slides up and down the Hmong language's eight tones; the father's voice, louder, slower, more vehement; and my interpreter's voice, mediating in Hmong and English, low and deferential in each. The hubbub summons sense-memories: the coolness of the red metal folding chair, reserved for guests, that was always set up when I arrived in the apartment; the shadows cast by the amulet that hung from the ceiling and swung in the breeze on its length of grocer's twine; the tastes of Hmong food. I sat on the Lees' red chair for the first lime on May 19, 1988. Earlier that spring I had come to Merced, California, because I had heard that there were some misunderstandings at the county hospital between its Hmong patients and medical staff. One doctor called them "collisions," which made it sound as if two different kinds of people had rammed into each other, head on, to the accompaniment of squealing brakes and breaking glass. As it turned out, the encounters were messy but rarely frontal. Both sides were wounded, but neither side seemed to know what had hit it or how to avoid another crash. I have always felt that the action most worth watching occurs not at the center of things but where edges meet. I like shorelines, weather fronts, international borders. These places have interesting frictions and incongruities, and often, if you stand at the point of tangency, you can see both sides better than if you were in the middle of either one. This is especially true when the apposition is cultural. When I first came to Merced, I hoped that the culture of American medicine, about which I knew a little, and the culture of the Hmong, about which I knew nothing, would somehow illuminate each other if I could position myself between the two and manage not to get caught in the crossfire. But after getting to know the Lees family and their daughter's doctors and realizing how hard it was to blame anyone, I stopped analyzing the situation in such linear terms. Now, when I play the tapes late at night, I imagine what they would sound like if I could splice them together, so the voices of the Hmong and those of the American doctors could be heard on a single tape, speaking a common language. 10. In line 17, "summons" most nearly means (A) sends for (B) calls forth (C) requests (D) orders (E) convenes 11. It can be inferred from lines 27-33 that "collisions" was NOT an apt description because the (A) clash between Hmong patients and medical staff was indirect and baffling (B) Hmong patients and the medical staff were not significantly affected by the encounters (C) medical staff was not responsible for the dissatisfaction of the Hmong patients (D) misunderstandings between the Hmong patients and the medical staff were easy to resolve (E) disagreement reached beyond particular individuals to the community at large

SAT真题阅读答案

第一套:0708 SECTION4:1-5ECBEC 6-10BDBDB 11-15AEABA 16-20BEAEC 21-23DEC SECTION6:1-5AADCB 6-10CBACB 11-15EAEBC 16-20ECDAD 21-25BBDAB SECTION9:1-5EBCCD 6-10ABDEC 11-15CCABA 16-19DCCE 第二套:0809 SECTION3:1-5EABAA 6-10EECCA 11-15DCEDC 16-20BEADC 21-24EEEB SECTION7:1-5DCABC 6-10CEEDB 11-15DBCDE 16-20ADEDA 21-24BACB SECTION9:1-5ABBDD 6-10DBAEB 11-15BDCCC 16-19DECE 第三套:0601 SECTION4:1-5DDACB 6-10EBCAB 11-15BACEC 16-20CDDEE 21-25ADBE

SECTION7:1-5ECAED 6-10EBACC 11-15AEABB 16-20DCEAB 21-24ABDB SECTION9:1-5BDEDE 6-10DACDD 11-15CBBAE 16-19DCCE 第四套:0605 SECTION3:1-5EEBED 6-10DEBDA 11-15EBDED 16-20ADBAC 21-24CBEC SECTION5:1-5CADCB 6-10EACBB 11-15ACEAE 16-20ECBCC 21-24DEEA SECTION8:1-5ACBDD 6-10EADEC 11-15AEBCC 16-19BEED 第五套:0610 SECTION2:1-5ABADC 6-10DBCAD 11-15BCEEB 16-20CAEBA 21-24DEEC SECTION5:1-5CBCAD 6-10BDCAB 11-15ECDDE 16-20EBEAD 21-24ACEE SECTION9:1-5BCBEB 6-10DCCEE

新SAT阅读真题原文解析

新SAT阅读真题原文解析 新SAT阅读真题原文来啦~和小编一起来看看SAT阅读都考了哪些内容吧! Unfortunately or fortunately, Nawab hadmarried early in life a sweet woman of unsurpassed fertility, whom he adored,and she proceeded to bear him children spaced, if not less than nine monthsapart, then not that much more. And all daughters, one after another afteranother, until finally the looked-for son arrived, leaving Nawab with acomplete set of twelve girls, ranging from toddler to age eleven, and one oddpiece. If he had been governor of the Punjab, their dowries would have beggaredhim. For an electrician and mechanic, no matter how light-fingered, thereseemed no question of marrying them all off. No moneylender in his right mindwould, at any rate of interest, advance a sufficient sum to buy the necessaryitems for each daughter: beds, a dresser, trunks, electric fans, dishes, sixsuits of clothes for the groom, six for the bride, perhaps a television, and onand on and on. Another man might have thrown up hishands—but not Nawabdin. The daughters acted as a spur to his genius, and helooked with satisfaction in the mirror each morning at the face of a warriorgoing out to do battle. Nawa b of course knew that he must proliferate hissources of revenue—the salary he received from K. K. Harouni for tending thetube wells would not even begin to suffice. He set up a one-room flour mill,run off a condemned electri c motor—condemne d by him. H e tried his hand atfish-farming in a pond at the edge o f one of his master’

SAT真题

SAT真题 做SAT免费的手机APP软件,随时做题随时测分,豌豆荚、应用汇、豌豆荚等应用商店搜Satonline就可下载啦或者去官网Satonline下载 1. Some fans feel that sports events are ______ only when the competitors are of equal ability, making the outcome of the game ______. A. successf ul…assured B. boring…questionable C. dull…foreseen D. interesting…predictable E. exciting…uncertain 2. Alfred Schnittke's musical compositions are ______: phrases are clipped, broken into sections, and split apart by long rests. A. garnished B. improvisational C. fragmented D. cautious E. uniform 3. The consumer advocate claimed that while drug manufacturers ______ the supposed advantages of their proprietary brands, generic versions of the same medications are often equally ______. A. tout…efficacious B. research…innocuous C. market…prohibitive D. laud…counterproductive E. extract…prescriptive 4. Latoya's _____ is shown by her ability to be ______: she can see her own faults more clearly than anyone else can. A. perceptiveness…self-centered B. objectivit y…restrictive C. cynicism…self-destructive D. open-mindedness…complacent E. insightfulness…self-critical 5. The bearded dragon lizard is a voracious eater, so ______ that it will consume as many insects as possible. A. abstemious

SAT阅读真题及答案解析(二)

SAT阅读真题及答案解析(二) SAT考试真题是很重要的备考资料,那么,很早以前的真题资料还有参考性吗?其实大家可以先以最近真题为主,以前的真题资料为辅进行练习。下面文都国际小编为大家整理了一篇SAT阅读真题及答案解析,供大家参考。 In the wake of the Industrial Revolution, when mass production became the pride and joy of nineteenth-century entrepreneurs, a fast-growing middle class reveled in the luxury of consumer goods, including jewelry, made available at economical prices. Prosperous segments of the population wanted to demonstrate their affluence, a development that provided a powerful stimulus to the jewelry industry in both Europe and the United States. 在工业革命苏醒之际,大规模生产变成了十九世纪企业家的骄傲和自豪。快速发展的中产阶级让奢侈品变成了大众消费品。百姓中富裕的人们想要显示自己的富裕。而这一因素的存在也快速激励了美国及欧洲的珠宝行业。 In this avalanche of mass production, many artists and artisans of the Arts and Crafts movement felt that the human touch, respect for materials, and the satisfaction of a fine finish were being lost. Jewelry, like other articles, was becoming impersonal, carelessly constructed, unimaginatively designed. Though labeled romantic and idealistic, some artists sought to produce individually conceived and executed pieces in workshop situations similar to those of medieval guilds. They wanted to produce, handmade jewelry from less-expensive materials for the general public, yet with the same care and commitment a court jeweler might apply to work for aristocratic clientele. In medieval times there had been artisans in towns and villages, working for ordinary people on a one-to-one basis; the adherents of the movement felt there was an urgency to return to this special relationship. It was considered particularly important that artists be involved to ensure the production of more meaningful objects, whether they be pottery, furniture, or, especially,

新SAT阅读真题二

新SAT阅读真题二 Exercise 2 This passage is excerpted from L.M. Montgomery, “The Gossip of Valley View,” originally published in 1910. It was the ?rst of April, and Julius Barrett, aged fourteen, perched on his father's gatepost, watched ruefully the low descending sun, and counted that day lost. He had not succeeded in "fooling" a single person, although he had tried repeatedly. One and all, old and young, of his intended victims had been too wary for Julius. Hence, Julius was disgusted and ready for anything in the way of a stratagem or a spoil. The Barrett gatepost topped the highest hill in Valley View. Julius could see the entire settlement, from "Young" Thomas Everett's farm, a mile to the west, to Adelia Williams's weather-grey little house on a moonrise slope to the east. He was gazing moodily down the muddy road when Dan Chester, homeward bound from the post of?ce, came riding sloppily along on his grey mare and pulled up by the Barrett gate to hand a paper to Julius. Dan was a young man who took life and himself very seriously. He seldom smiled, never joked, and had a Washingtonian reputation for veracity. Dan had never told a conscious falsehood in his life; he never even exaggerated. Julius, beholding Dan's solemn face, was seized with a perfectly irresistible desire to "fool" him. At the same moment his eye caught the dazzling re?ection of the setting sun on the windows of Adelia Williams's house, and he had an inspiration little short of diabolical. "Have you heard the news, Dan?" he asked. "No, what is it?" asked Dan.

可汗学院新SAT阅读真题下载(68篇)

可汗学院新SAT阅读真题下载 到目前为止,新版SAT可汗学院官方不断放出更多真题,已经放出了68篇阅读,具体如下:Level 2 22篇,Level 3 21篇,Level 4 17篇,8篇Diagnostic Quiz,共68篇阅读! 想要下载可汗学院68篇阅读真题的同学,请移步:https://www.360docs.net/doc/6d1327979.html,/sat/news/603917.html Level 2Science篇1 Passage adapted from Nikhil Swaminathan, "Eat (Less) to Live (Longer)," ?2007 by Scientific American. Scientists have known for more than 70 years that the one surefire way to extend the lives of animals was to cut calories by an average of 30 to 40 percent. The question was: Why? Now a new study begins to unravel the mystery and the mechanism by which reducing food intake protects cells against aging and age-related diseases. Researchers report in the journal Cell that the phenomenon is likely linked to two enzymes—SIRT3 and SIRT4—in mitochondria (the cell's powerhouse that, among other tasks, converts nutrients to energy). They found that a cascade of reactions triggered by lower caloric intake raises the levels of these enzymes, leading to an increase in the strength and efficiency of the cellular batteries. By invigorating the mitochondria, SIRT3 and SIRT4 extend the life of cells, by preventing flagging mitochondria from developing tiny holes (or pores) in their membranes that allow proteins that trigger apoptosis, or cell death, to seep out into the rest of the cell. "We didn't expect that the most important part of this pathway was in the mitochondria," says David Sinclair, an assistant professor of pathology at Harvard Medical School and a study co-author. "We think that we've possibly found regulators of aging." In 2003 Sinclair's lab published a paper in Nature that described the discovery of a gene that switched on in the yeast cell in response to calorie restriction, which Sinclair calls a "master regulator in aging." Since then, his team has been searching for an analogous gene that plays a similar role in the mammalian cell. The researchers determined from cultures of human embryonic kidney cells that lower caloric intake sends a signal that activates a gene inside cells that codes for the enzyme NAMPT (nicotinamide phosphoribosyltransferase). The two- to four-fold surge in NAMPT in turn triggers the production of a molecule called NAD (nicotinamide adenine dinucleotide), which plays a key role in cellular metabolism and signaling. The uptick in NAD levels activates the SIRT3 and SIRT4 genes, increasing levels of their corresponding SIRT3 and SIRT4 enzymes, which then flood the interior of the mitochondria. Sinclair says he's not sure exactly how SIRT3 and SIRT4 beef up the mitochondria's energy output, but that events leading to cell death are at the very least delayed when there are vast quantities of the enzymes. SIRT3 and SIRT4 are part of a family called sirtuins (SIRT1, which helps extend cell life by modulating the number of repair proteins fixing DNA damage both inside and outside the cell's nucleus, is also a member). SIRT is short for sir-2

相关主题
相关文档
最新文档