选课中心
7099人选课
GRE公开讲座
0元
GMAT公开讲座
0元
一对一体验课
99元
GRE模考网站
10000人
托福TPO模考网站HOT
39209人预约
GRE辅导课程
17537 人
GMAT辅导课程
17537 人
托福辅导课程
17537 人
【定制】1v1
私人订制
资料下载
考前冲刺
扫码关注掌握一手留学资讯
回复XDF免费领
水平测试和备考资料
扫码关注公众号
【GRE阅读题目解析:人体细胞修复效率随年龄增长减弱】GRE考试考什么?GRE阅读是重点。新东方在线GRE频道为大家带来GRE阅读题目解析:人体细胞修复效率随年龄增长减弱,答案见下一页,希望对大家GRE备考有所帮助。更多精彩尽请关注新东方在线GRE频道!
查看全部:GRE阅读答案解析(汇总)
GRE阅读题目解析:人体细胞修复效率随年龄增长减弱
P2
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, 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 (NH2) 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. (454 words)
For the following question, consider each of the choices separately and select all that apply
3. According to the passage, which of the following is NOT characteristic of enzymatic glycosylation of proteins?
(A) Proteins affected by the process are made unstable.
(B) Glucose attachment impairs and stiffens tissues.
(C) Glucose is attached to proteins for specific purposes.
4. According to the passage, which of the following statements is true of Amadori products in proteins?
(A) They are more plentiful in a dehydrated environment.
(B) They are created through enzymatic glycosylation.
(C) They are composed entirely of glucose molecules.
(D) They are derived from Schiff bases.
(E) They are derived from AGE's.
5. Which of the following best describes the function of the third paragraph of the passage?
(A) It offers evidence that contradicts the findings described in the first two paragraphs.
(B) It presents a specific example of the process discussed in the first two paragraphs.
(C) It explains a problem that the researchers
mentioned in the second paragraph have yet to solve.
(D) It evaluates the research discoveries described in the previous paragraph.
(E) It begins a detailed description of the process introduced in the previous two paragraphs.
6. The passage suggests that which of the following would be LEAST important in determining whether nonenzymatic glycosylation is likely to have taken place in the proteins of a particular tissue?
(A) The likelihood that the tissue has been exposed to free glucose
(B) The color and spectrographic properties of structures within the tissue.
(C) The amount of time that the proteins in the tissue have persisted in the body
(D) The number of amino groups within the proteins in the tissue
(E) The degree of elasticity that the tissue exhibits
资料下载
GRE佛脚2024增补包含最新热词与六选二整理
发布时间:2022-06-06添加新东方在线美研助教号
回复【资料】获取
GRE-PPO模考完整套题+解析资料下载
发布时间:2022-06-06添加新东方在线美研助教号
回复【资料】获取
GRE佛脚词汇表网络版资料下载
发布时间:2022-05-21添加新东方在线美研助教号
回复【资料】获取
2024GRE佛脚填空机经系列资料下载
发布时间:2022-04-15添加新东方在线美研助教号
回复【资料】获取
2024GRE佛脚阅读系列资料下载
发布时间:2022-04-15添加新东方在线美研助教号
回复【资料】获取
2024杨鹏阅读难句(GMAT+GRE)教程资料下载
发布时间:2022-04-15添加新东方在线美研助教号
回复【资料】获取
GRE PPO模考完整练习题(答案)
发布时间:2019-12-10添加新东方在线美研助教号
回复【资料】获取
GRE写作题库解析【Issue/Argument】
发布时间:2019-12-10添加新东方在线美研助教号
回复【资料】获取
GRE阅读机经及官方真题资料练习
发布时间:2019-12-10关注新东方在线美研订阅号
回复【GRE】获取
GRE填空机经佛脚系列资料持续更新…
发布时间:2019-12-10添加新东方在线美研助教号
回复【资料】获取
GRE佛脚词汇修订版PDF电子版下载
发布时间:2019-12-10添加新东方在线美研助教号
回复【资料】获取
【提升英语必看】英语记录片/演讲/美剧合集
发布时间:2019-11-27添加新东方在线美研助教号
回复【资料】获取
《华尔街日报》、《纽约时报》英文报刊合集
发布时间:2019-11-27添加新东方在线美研助教号
回复【资料】获取
【必看】美国研究生申请注意事项
发布时间:2019-11-27添加新东方在线美研助教号
回复【资料】获取
美国研究生录取分数&截止日期信息汇总
发布时间:2019-11-27添加新东方在线美研助教号
回复【资料】获取
2020美国研究生热门专业院校排名
发布时间:2019-11-27添加新东方在线美研助教号
回复【资料】获取
GRE模考套题、机经汇总
发布时间:2019-11-27添加新东方在线美研助教号
回复【资料】获取
添加美研助教号,
回复【GRE】获取备考必看资料包
推荐阅读
更多>>备考GRE,对大部分同学来说也是一个新挑战,尤其是阅读部分,如何在有限的时间内大幅提高阅读速度呢? 快来本文看看吧。
本文今天为大家带来的是gre考试中easy等级难度的阅读片段,一起来看看吧!
2022年3月13-19日GRE阅读题回忆及答案(六)来啦,来本文和新东方在线GRE一起来看看详细信息吧。
2022年3月13-19日GRE阅读题回忆及答案(五)来啦,来本文和新东方在线GRE一起来看看详细信息吧。
2022年3月13-19日GRE阅读题回忆及答案(四)来啦,来本文和新东方在线GRE一起来看看详细信息吧。
2022年3月13-19日GRE阅读题回忆及答案(三)来啦,来本文和新东方在线GRE一起来看看详细信息吧。
2022年3月13-19日GRE阅读题回忆及答案(二)来啦,来本文和新东方在线GRE一起来看看详细信息吧。
2022年3月13-19日GRE阅读题回忆及答案(一)来啦,来本文和新东方在线GRE一起来看看详细信息吧。
2022年2月13日GRE阅读题回忆及答案来啦,来本文和新东方在线GRE一起来看看详细信息吧。
2022年2月13日GRE阅读题回忆及答案来啦,来本文和新东方在线GRE一起来看看详细信息吧。
添加美研助教号,
回复【GRE】获取备考必看资料包
资料下载
更多>>添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
关注新东方在线美研订阅号
回复【GRE】获取
添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
添加新东方在线美研助教号
回复【资料】获取
阅读排行榜
相关内容