问题 问答题 简答题

蛋白质周转的含义及意义。

答案

参考答案:

机体蛋白质代谢是一个动态平衡过程,机体在合成新的蛋白质的同时,也存在旧的蛋白质的降解,降解产生的AA又可用于合成蛋白质,这种现象叫蛋白质周转。

意义:

⑴周转是调节细胞内特异酶含量的需要,在一定生理或病理情况下,某一代谢途径需要加快或减慢,其限速酶的合成或降解也相应提高,以适应代谢调节的需要。

⑵周转是适应营养、生理和病理变化的需要,如饥饿时糖异生加强以维持血糖浓度,在原料主要来自肌肉蛋白降解产生的Gln和Ala,及其他生糖AA,同时蛋白降解产生的BCAA在肝外氯化以供能,又如疾病条件下,动物采食量降低,肝蛋白尤其是免疫球蛋白合成率需提高,此时肌肉蛋白降解率增加,产生的AA供肝的合成所需。

⑶周转是清除体内异常蛋白质的需要,机体蛋白受外界影响或者毒化或毒变性,会干扰细胞的正常代谢,必须降解除去。另外,由于DNA突变,指导合成的异常蛋白也必须降解。

⑷蛋白质周转是构造细胞的需要,对维持细胞内蛋白质稳定,细胞体积和形状,组织生长速度和体积,以及创伤组织的修复都是必需的。

单项选择题

Passage Three

Uffizi Tries to Outdo Louvre
Uffizi试图胜过卢浮宫
Italy is to try to turn the Uffizi gallery in Florence into Europe’s premier art museum, with an ambitious 56m euro scheme to double its exhibition space.
Giuliano Urbani, Italy’s culture minister, said the enlarged gallery would surpass "even the Louvre".
By the time work is completed, visitors to the extensively remodeled Uffizi will be able to see 800 new works, including many now confined to the gallery’s storerooms for lack of space.
The project—the outcome of nine months of intensive work by a team of architects, engineers and technicians—is a centrepiece of the cultural policy of Silvio Berlusconi’s government.
With refurbishment plans also afoot for the Accademia in Venice and the Brera in Milan, Italy is bent on securing its share of a market for cultural tourism that is threatened not just by the Louvre, but also by the " art triangle" of Madrid, which takes in the Prado, the Thyssen collection and the Reina Sofia museum of art.
Schemes for the expansion of the Uffizi’s exhibition space stretch back almost 60 years. The latest was mooted in the mid-1990s.
But the one adopted by the present Italian government has reached a far more advanced stage than any of its forerunners. Roberto Cecchi, the government official in charge of the project, said yesterday that all that remained to do was to tender for contracts.
The first changes will be seen as early as next week when a collection of pictures by Caravaggio and his school, including the artist’s Bacchus, currently crammed into a tiny room on the second floor, is to be moved to more expansive premises on the first.
Mr.Cecchi said the biggest problem faced by his team was "inserting a museum into a building that is itself a monument". The horseshoe-shaped Palazzo degli Uffizi, began in 1560, was designed by the artist and historian Giorgio Vasari.
The latest plans are bound to stir controversy, involving as they do the creation of new stairwells and lifts in the heart of the building. There has already been an outcry over one proposed element, a seven-storey, canopy-like structure for a new exit by the Japanese architect Arata lsozaki.
But Mr.Urbani said in Florence on Tuesday that part of the scheme was "subject to further evaluation".
At the heart of the plan is the opening up of the first floor of the vast building, which for decades was occupied by the local branch of the national archives.
This will allow visitors to follow a more extensive, and ordered, itinerary that would turn the Uffizi into what Antonio Paolucci, Tuscany’s top art official, called "a textbook of art history".
As at present, visitors will be channelled to the second floor, where they will be able to study early works by Cimabue and Giotto before moving on to admire the gallery’s extraordinary collection of Renaissance masterpieces, including Botticelli’s Primavera.
But most of what was painted after 1500 is to be moved down a storey to new exhibition space, and on the ground floor there will be a more extensive collection than at present of modern art. The overall increase in exhibition space will be from 6,000sq metres to almost 13,000.
Asked if the expansion might not increase the risk of inducing Stendhal’s syndrome—the disorientation, noted by the French novelist, in those who encounter dozens of Italian Renaissance masterpieces—Mr. Cecchi replied fatalistically, "Yes. It’ll double it".

The fact that a group of architects, engineers and technicians spent nine months on the projec! shows that______.

A.it was a large-scale project involving collaboration of experts from various fields

B.it was completed at amazing speed

C.the government attached great importance to the project

D.the government was following the correct cultural policy

多项选择题