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
As people age, their cells become less efficient and less able replace damaged components. At the same time their tissues stiffe
As people age, their cells become less efficient and less able replace damaged components. At the same time their tissues stiffe
admin
2010-02-20
7
问题
As people age, their cells become less efficient and less able replace damaged components. At the same time their tissues stiffen, For example the lungs and the heart muscle expand less successfully, the blood vessels become increasingly rigid, and the ligaments and tendons tighten.
Few investigators would attribute such diverse effects to a single cause. Nevertheless, researchers have discovered that a process long known to discolor and toughen foods may also contribute to age-related impairment of both cells and tissues. That process is nonenzymatic glycosylation, whereby glucose becomes attached to proteins without the aid of enzymes. When enzymes attach glucose to proteins( enzymatic glycosylation), they do so at a specific site on a specific protein molecule for a specific purpose. In contrast, the nonenzymatic process adds glucose haphazardly to any of several sites along any available peptide chain within a protein molecule.
This nonenzymatic glycosylation of certain proteins has been understood by food chemists for decades, although few biologists recognized until recently that the same steps could take place in the body. Nonenzymatic glycosylation begins when an aldehyde group (CHO) of glucose and an amino group (HN2) of a protein are attracted to each other. The molecules combine, forming what is called a Schiff base within the protein. This combination is unstable and quickly rearranges itself into a stabler, but still reversible, substance known as an Amadori product.
If a given protein persists in the body for months or years, some of its Amadori products slowly dehydrate and rearrange themselves yet again, into new glucose-derived structures. These can combine with various kinds of molecules to form irreversible structures named advanced glycosylation end products ( AGE’s). Most AGE’s are yellowish brown and fluorescent and have specific spectrographic properties. More important for the body, many are also able to cross-link adjacent proteins, particularly ones that give structure to tissues and organs. Although no one has yet satisfactorily described the origin of all such bridges between proteins, many investigators agree that extensive cross-linking of proteins probably contributes to the stiffening and loss of elasticity characteristic of aging tissues.
In an attempt to link this process with the development of cataracts ( the browning and clouding of the lens of the eye as people age), researchers studied the effect of glucose on solutions of purified crystallin, the major protein in the lens of the eye. Glucose-free solutions remained clear but solutions with glucose caused the proteins to form clusters, suggesting that the molecules had become cross-linked. The clusters diffracted light, making the solution opaque. The researchers also discovered that the pigmented cross-links in human cataracts have the brownish color and fluorescence characteristic of AGE’s. These data suggest that nonenzymatic glycosylation of lens crystallins may contribute to cataract formation.
According to the passage, which of the following statements is true of the process that discolors and toughens foods?
选项
A、It takes place more slowly than glyeosylation in the human body.
B、It requires a higher ratio of glucose to protein than glycosylation requires in the human body.
C、It does not require the aid of enzymes to attach glucose to protein.
D、It proceeds more quickly when the food proteins have a molecular structure similar to that of crystallin proteins.
答案
C
解析
该题问:根据文章,下面哪一个关于使食物失色干燥的过程的说法是否正确?C项意为“它无需酶的帮助也能把葡萄糖依附于蛋白质”。A项意为“它比人体内糖基化过程进行(发生)得更慢”;B项意为“它需要比人体内糖基化所需的葡萄糖、蛋白比例更高”;D项意为“当食物蛋白具有和晶体状蛋白相似的结构时,它进行得更快”。
转载请注明原文地址:https://www.kaotiyun.com/show/vlvO777K
0
专业英语八级
相关试题推荐
TheUnitedStateshasmovedbeyondtheindustrialeconomystagetothepointwhereithasbecometheworld’sfirstserviceecono
A、ThemenuofMcDonald’sinBrazilisspeciallymadetocatertolocaltaste.B、BrazilianMcDonald’sandaresimilarintheirou
A、Tissueculture.B、Mapping.C、Solarenergy.D、Weightlessness.C
Middlebornchildrenwilltellyouthattheyusuallydidn’tfeelallthatspecialwhilegrowingup.Thefirstbornhadhisspot-
Weoftenhearandreadaboutcontroversialissuesinscienceandtechnology.Forexample,willradiationfromelectronicequipm
Weoftenhearandreadaboutcontroversialissuesinscienceandtechnology.Forexample,willradiationfromelectronicequipm
Weoftenhearandreadaboutcontroversialissuesinscienceandtechnology.Forexample,willradiationfromelectronicequipm
A、Onlycollegegraduatesneedtolookforajob.B、Nomatterhowdifficultitis,collegestudentsshouldatleasttrytwiceto
A、Asportsreporter.B、AnOlympicGamesplayer.C、Aschooldirector.D、Amarathonrunner.C
A、TohelpmonitortheZikadiseasemoreeffectively.B、Toprovidemoreopportunitiesforthedisabledathletes.C、Toavoidthes
随机试题
为使药物中的药效成分充分煎出,又不会造成药效成分流失,需要后下的中药是
MG起病隐袭,首发症状多为一侧或双侧________肌麻痹,但________括约肌一般不受累。
患者,男性,33岁,左侧肩背部有约3cm×4cm的紫红色隆起,质硬,中心有多个脓栓,中央部坏死呈火山口状,查体:体温38.6℃,偶有寒战。引起该疾病的主要致病菌为
路面横坡可以采用()进行测试。
某工程项目为赶工期而昼夜施工,严重影响了相邻小区居民的休息,经现场劝阻无效,居民便成立维权小组与该施工企业谈判,要求其停止夜间施工,并赔偿2万元作为抚慰金。关于该施工企业与相邻小区居民之间的关系,以下表述中正确的是()。
下列选项中不属于基金职业道德教育途径的是()。
房地产投资信托基金起源于()。
美育是对受教育者的__________和审美能力的教育。
区位优势,是指跨国企业在投资区位上所具有的选择优势。即可供投资地区是否在某些方面较国内具有优势,投资区位的选择要受到生产要素和市场的地理分布、生产要素和运输成本、投资环境等诸因素的影响。根据以上定义,下列不具有区位优势的是:
一切有利于生产力发展的方针政策都是符合人民根本利益的,改革开放有利于生产力的发展,所以改革开放是符合人民根本利益的。以下哪种推理方式与上面的这段论述最为相似?
最新回复
(
0
)