糖酵解产生的丙酮酸和NADH的去路

糖酵解产生的丙酮酸和NADH 的去路：有氧情况下丙酮酸从胞质进入线粒体，进行有氧代谢。而EMP 途径生成NADH 由于不能及时被氧化成NAD+而有可能导致EMP 途径第6步反应缺少辅酶NAD+而使反应速度下降（细胞中的辅酶分子是有限的，必须循环使用。NADH 须随时恢复其氧化状态NAD +，才能周而复始地参与此类酶的催化反应）。又由于NADH 不能直接进入线粒中进行氧化，所以它必须将氢转移给能穿过线粒体膜的受氢体，通过受氢体的转运而把氢从胞质带入线粒体内，这种作用称为穿梭作用。目前了解比较多的是苹果酸穿梭作用（见图8-2）和3-磷酸甘油穿梭作用（见图8-3）。这两种作用使胞质中的NADH 氧化为NAD +，使其浓度恢复到反应前的水平。氧化脱下的氢以穿梭分子的一

部分被带到线粒体内,并在呼吸链中氧化生成水且伴有氧化磷酸反应产生能量货币物质ATP 。

H 2

C OH H C OH H 22C OH C =O

2C-O-NDH +

NADH+ H + H 2C OH

H C OH

H 2C-O-H 2C OH

C =O

H 2C-O-胞液

线粒体衬质 外膜 图8-3 3-磷酸甘油穿梭 FPG ：内膜3-磷酸甘油脱氢酶；Fpi ：（FPint ）：内NADH 脱氢酶 图8-2 苹果酸穿梭作用（Ⅰ.苹果酸-α酮戊二酸反向载体蛋白，Ⅱ.天冬氨酸-谷氨酸反向载体蛋白）

线粒体衬质

NAD +

2

生成乙酰辅酶A：丙酮酸在有氧气和线粒体存在时进入线粒体，经丙酮酸脱氢酶复合体（表5-1-2）催化氧化脱羧产生NADH、CO2和乙酰辅酶A，乙酰辅酶A进入三羧酸循环和氧化磷酸化彻底氧化为CO2和H2O，释放的能量在此过程中可产生大量ATP。这是糖的有氧氧化过程。糖的有氧氧化是机体获得ATP的主要途径。

表5-1-2 丙酮酸脱氢酶复合体的组成

丙酮酸生成乙酰辅酶A的反应是糖有氧氧化过程中重要的不可逆反应（图4-1-14）。丙酮酸脱氢产生NADH+H+，释放的自由能则贮于乙酰辅酶A中。乙酰辅酶A可参与多种代谢途径。

丙酮酸脱氢酶系的多种辅酶中均含有维生素，TPP中含有维生素B1，辅酶A（HSCoA）中含有泛酸，FAD含有维生素B2，NAD+含尼克酰胺（维生素PP）。所以，当这些维生素缺乏，特别是维生素B1缺乏时，丙酮酸及乳酸堆积，能量生成减少，可发生多发性末梢神经炎，严重时可引起典型脚气病。

自我介绍(self-introduce)

Good morning. I am glad to be here for this interview. First let me introduce myself. My name is ***, 24. I come from ******,the capital of *******Province. I graduated from the ****** department of *****University in July ,2010.In the past two years I have been prepareing for the postgraduate examination while I have been teaching *****in NO.****middle School and I was a head-teacher of a class in junior grade two.Now all my hard work has got a result since I have a chance to be interview by you.

I am open-minded ,quick in thought and very fond of history.In my spare time,I have broad interests like many other youngers.I like reading books, especially those ****.Frequently I exchange with other people by making comments in the forum on line.In addition ,during my college years,I was once a Net-bar technician.So, I have a comparative good command of network application.I am able to operate the computer well.I am skillful in searching for information in Internet.I am a football fan for years.Italian team is my favorite.Anyway,I feel great pity for our country’s team.

I always believe that one will easily lag behind unless he keeps on learning .Of course, if I am given a chance to study ****** in this famous University,I will stare no effort to master a good command of advance ******.

Hello, my professors.It's a fine day today,and i'm very pleased to meet you here.First of all,i'd like to introduce myself to you.My name is ***,my hometown is ***,which is a really beautiful city.Even when i was a young boy,i was very interested in biology science.Every one may have a dream,and i still remember that my dream is to be a biology scientist (just like ZHU KE ZHEN).I liked to make wonders just like,where are we from?Where are we going in the universe?And then i would find the answers in book by myself.Still today i think that interest is the best teacher in one's whole life (and knowledge comes from practice).

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into products in all of the modern industry.

Four years' university education gives me a lot of things to learn,a lot of chances to try,and a lot of practices to improve myself.It teaches me not only what to study and how to think,but also to see the importance of practical ability (such as doing expriment as much as possible). In the university life,i have made many good friends.They help me improve my study and research ability, do ererything just like a man,and often give me good example to follow.

Besides what i have introduced myself above,i also have many interests in my spare time.I like playing football,which is an effective way i think to improve my body health,and it can teach me how to join in a group and deal with other people.Drawing and writing is another favor to me.

Above all,i choose the major in order to broad my view in biology scince,and enhance my research ability.I will do my best to join the new group and be good at postgraduate study.