首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
According to the free-radical theory, why does aging occur?
According to the free-radical theory, why does aging occur?
admin
2018-08-16
71
问题
According to the free-radical theory, why does aging occur?
Listen to part of a lecture in a biology class.
Professor: Aging of course is a natural part of life for all living things. Most theories of aging, of why aging occurs, fall into one of two categories. First, you have the biological clock category—theories in this category assert that all organisms have a sort of internal biological clock, that they are sort of genetically programmed to age in a certain age at a certain rate. The second category asserts that aging is the result of the gradual accumulation of damage to cells and tissues. In the second category, we have a theory called "the free radical theory," which we’ll now examine.
According to this theory, an organism’s cells in their regular metabolic processes—by metabolic processes I mean... things like cellular respiration and reproduction... in their regular metabolic processes, cells generate oxygen molecules, some of which have an extra electron. That extra or free electron makes the whole molecule unstable. The unstable molecule is known as a free radical, okay?
And according to this theory these free radicals cause damage to other molecules and structures within the cell, including, most significantly, to the cell’s DNA, and it’s this gradual degradation of DNA and tissues and larger structures that drives the aging process.
You may be wondering how does this theory hold up? Well, some organisms do have some protection against free radical damage in the form of substances called antioxidants. Antioxidants through a series of chemical reactions, can help stabilized free radicals, so they can’t damage the cell. An important antioxidant is an enzyme called "superoxide dismutase" (or SOD). ln experiments with fruit flies, when researchers increased the level of SOD, there was less free radicals harm. The fruit flies had longer lifespans and stayed younger longer. So this seems to show that indeed, at least in some invertebrates, free radical damage is what causes aging.
Ok, and there is another line of thought that at one point was used to support the free radical theory. It was discovered that when organisms, such as yeast—a fungus—were given a calorie restricted diet, they lived longer. If their diets included far fewer calories than normal but still included all the necessary nutrients, their lifespan increased. For a while researches explained this by arguing that the limited food intake leads the yeast cell’s metabolism to slow down. You’ll need to remember that according to the free radical theory, cells metabolic processes were what brought about those extra electrons that created free radicals, and, so the argument went at the time, if the cells metabolism slowed down, the rate of free radical production also slowed down, so there was less cell damage. And that’s why the yeast cells aged slower and lived longer.
However, later research, this time on roundworms, suggested that while it was true that organisms on a calorie restricted diet live longer, it wasn’t because of a slower metabolism. In fact, the researchers in this roundworm study claimed that the special diet actually increased cell respiration, and what happened was this increased respiration activated a certain gene, a gene that has been linked to a longer lifespan. And these researchers claimed that it was actually the activation of this longevity gene, not the slowing of free radical damage, that lengthen the lifespan.
选项
A、Antioxidants damage various cell structures.
B、Unstable oxygen molecules damage cells’ DNA.
C、Antioxidants begin interfering with cell metabolism.
D、Cells begin producing fewer free radicals.
答案
B
解析
细节题。在介绍自由基导致衰老的理论中,教授介绍道:free radicals cause damage to other molecules and structures within the cell,including,most significantly,to the cell’s DNA,即自由基损坏分子和细胞DNA,导致了衰老,因此B选项是正确答案。抗氧化剂的作用是使自由基稳定从而使细胞不受损害,因此并不是破坏细胞结构,也不是干扰细胞新陈代谢,即A选项和C选项不正确。该部分未提到自由基的数量少会导致衰老,因此D选项不正确。
转载请注明原文地址:https://kaotiyun.com/show/dNfO777K
0
托福(TOEFL)
相关试题推荐
Completethetablebelow.WriteNOMORETHANTHREEWORDSAND/ORANUMBERforeachanswer.
ChooseTHREEletters,A-G.WhichTHREEfactorsshouldthestudentconsiderwhileselectingcourses?AclasstimeBcoursetopic
Completethenotesbelow.WriteNOMORETHANTHREEWORDSforeachanswer.GIVINGASPEECHReasonsfornervousnessLecturers
Whatproblemsdothespeakersidentifyforthisproject?ChooseSEVENanswersfromtheboxandwritetheletters,A-H,nexttoq
Whatfeaturedothespeakersidentifyforeachofthefollowingcourses?ChooseFIVEanswersfromtheboxandwritethecorrect
Whatfeaturedothespeakersidentifyforeachofthefollowingcourses?ChooseFIVEanswersfromtheboxandwritethecorrect
Choosethecorrectletter,A,BorC.Whatkindofskillwillthestudentgaininthecourse?
Choosethecorrectletter,A,BorC.ReflectiveJournalAssignmentWhatshouldbefirstlyincludedinthereflectivejournal?
Choosethecorrectletter,A,BorC.Whatistheguestexpectedtoovercomewhensufferingfromcultureshock?
Whatadvantagedoesthespeakermentionforeachofthefollowingphysicalactivities?ChooseSIXanswersfromtheboxandwrite
随机试题
契约型基金与公司型基金的区别有()。
因税务机关的责任,致使纳税人少缴税款的,税务机关可以在3年内要求纳税人补缴,并加收滞纳金。()
测评目的具有隐蔽的品德测评法是()
I’vebecomegoodfriendswithseveralofthestudentsinmyschool______ImetintheEnglishspeechcontestlastyear.
广州、深圳、佛山三市的新产品开发项目数占珠三角地区的新产品比例为()。
在我国历史上,“百家争鸣”的鼎盛时期是()。
张小珍:在我国,90%的人所认识的人中都有失业者,这真是个令人震惊的事实。王大为:我不认为您所说的现象有令人震惊之处。其实,就5%这样可接受的失业率来讲,每20个人中就有1个人失业。在这种情况下,如果一个人所认识的人超过50个,那么,其中就很可能
在面向对象方法中,不属于“对象”基本特点的是
Ourtheoryandpracticeintheareaofsentencinghaveundergoneagradualbutdramaticmetamorphosisthroughtheyears.Primiti
Thelongyearsoffoodshortageinthiscountryhavesuddenlygivenwaytoapparentabundance.Storesandshopsarechokedwith
最新回复
(
0
)