共用题干 第三篇Eat More, Weigh Less, Live LongerClever genetic detective work may have found out the reason why a near-starvation diet prolonas the life of many animals.Ronald Kahn at Harvard Medical School in Boston,U.S.,and his colleagues navebeen able to extend the lifespan(寿命)of mice by 18 per cent by blocking the rodent's(啮齿动物)increase of fat in specific cells.This suggests that thinness一and not necessarily diet一Iromotes lonq life in"calorie(热量卡)restricted" animals."It's very cool work",says aging researche:Cynthia Kenyon of the University ot California, San Francisc."These mice eat all they want, lose weight and live longer.It's like heaven."Calorie restriction dramatically extends the lifespan of organisms as different as worms and rodents.Whether this works in humans is still unknown,partly because few people are willina to submit to such a strict diet.But many researchers hope they will be able to trigger the same effect with a drug once they understand how less food leads to a longer life.One theory is that eating less reduces the increase of harmful things that can damage cells.But Kahn's team wondered whether the animals simply benefit by becoming thin.To find out, they used biology tricks to disrupt the insulin(胰岛素)receptor (受体)gene in lab mice一but only in their fat cells."Since insulin is needed to help fat cells storefat ,these animals were protected against becoming fat,"explains Kahn.This slight genetic change in a single tissue had dramatic effects.By three months of age.Kahn's modified mice had up to 70 per cent less body fat than normal control mice,despite the fact that they ate 55 per cent more food per gram of body weight.In addition ,their lifespan increased.The average control mouse lived 753 days,while the thin rodents averaged a lifespan of 887 days.After three years,all the control mice had died.but one-quarter of the modified rodents were still alive."That they ciet these effects by just manipulating the fat cells is controversial,"saysLeonard Guarente of the Massachusetts Institute of Technology,who studies calorie restriction and aging.But Guarente says Kahn has yet to prove that the same effect is responsible forincreased lifespan in calorie-restricted animals."It might be the same effect or there might be two routes to long life,"he points out,"and that would be very interesting." Ronald Kahn and his colleagues can make mice live longer by
A.offering them less food. B.giving them a balanced diet. C.disrupting the specific genes in their fat cells. D.Dreventina them qrowinq larger.正确答案C
