首页
登录
职称英语
As people age, their cells become less efficient and less able to replace dam
As people age, their cells become less efficient and less able to replace dam
游客
2023-12-19
54
管理
问题
As people age, their cells become less efficient and less able to 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, al though few biologists recognized until recently that the same steps could take place in the body. Nonenzyrnatic glycosylation begins when an aldehyde group (CHO) of glucose and an amino group (NH2) of a protein are at tracted to each other. The molecules combine, forming what is called a Sehiff 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. There data suggest that nonanzymatic glycosylation of lens crystallins may contribute to cataract formation. (454) [br] According to the passage, which of the following statements is true of Amadori products in proteins?
选项
A、They are created through enzymatic glycosylation.
B、They are composed entirely of glucose molecules.
C、They are derived from Schiff bases.
D、They are derived from AGE’s.
答案
C
解析
事实细节题。根据第三段最后两句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.可知Amadori是由Schiff base衍生而来,因此C项为正确答案。
转载请注明原文地址:https://tihaiku.com/zcyy/3285568.html
相关试题推荐
Inourlooks-obsessedsociety,manypeoplethinkthatbeingoverweightisan
Inourlooks-obsessedsociety,manypeoplethinkthatbeingoverweightisan
Inourlooks-obsessedsociety,manypeoplethinkthatbeingoverweightisan
Inourlooks-obsessedsociety,manypeoplethinkthatbeingoverweightisan
Inourlooks-obsessedsociety,manypeoplethinkthatbeingoverweightisan
Inourlooks-obsessedsociety,manypeoplethinkthatbeingoverweightisan
Inourlooks-obsessedsociety,manypeoplethinkthatbeingoverweightisan
Inourlooks-obsessedsociety,manypeoplethinkthatbeingoverweightisan
Inourlooks-obsessedsociety,manypeoplethinkthatbeingoverweightisan
Inourlooks-obsessedsociety,manypeoplethinkthatbeingoverweightisan
随机试题
InthebookMenAreFromMars,WomenAreFromVenus,theauthorstatesthat
OnPublicSpeakingI.People’sfrequentresponsetogivi
随着生活水平的提高,越来越多的中国人对骑马产生浓厚的兴趣。Withtheimprovementoflivingstandards,anincrea
【教案】 TeachingAims: Knowledgeaim:Studentswillknowwhatsensegroupisan
与子宫内膜癌预后关系最为密切的是A.年龄 B.肥胖 C.子宫内膜癌发生部位
火焰烧伤现场急救时,下列哪项不正确A.使用灭火器灭火 B.用大衣毯子棉被覆盖灭
幼儿教师的表达能力是教师口语。
有以下()情形的,不得担任股份有限公司的董事。A:限制民事行为能力者 B:因犯
从事化妆品生产的纳税人发生视同销售行为,若无同类应税消费品的销售价格,则其组成计
女,27岁。因分娩大出血急需输血。当地血站距医院较远无法及时提供,其他医院也无血
最新回复
(
0
)