生物讨论专区

darksider

原帖由 白羊座aries 于 2009/11/2 02:17 PM 发表
问下ATP synthetase 和 整个oxidative phosphorylation 是怎样操作的?为什么没有oxygen就没有kreb cycle?就因为oxygen是act as final acceptor for oxidative phosphorylation,所以没有O2就没有kreb cycle?没有 oxida ...

If there is no oxygen, kreb cycle wouldn't occur. Only substrate-level phosphorylation wiill occur. This is because in order for ETS to work, you need oxygen which acts as the final electron acceptor.Oxygen will accept electrons from the cytochrome oxidase to oxidise it. Also If cytochrome oxidase is not functional(when inhibited by some poisons), the whole activity would be interrupted.  

If oxygen is absent or when cytochrome c oxidase is damaged, the electrons from NADP+H+ and FADH2 will be taken up by NAD+ and FAD+ to form NADP+H+ and FADH2. Please refer to my post below.

[ 本帖最后由 darksider 于 4-11-2009 02:54 AM 编辑 ]

bell_25

哦。。我明白了。。原来gene和codon是不同的东西。。谢谢

我知道Dark reaction is the light independent reaction in photosynthesis..
可是。。我从一本书上看到这个statement。。所以我想问到底对不对。。
Dark reaction is the stage of photosynthesis that does not need light.
It could occur in light or in the dark.
因为我一直以为dark reaction is occurred in darkness..

Allison

Dark reaction is the stage of photosynthesis that does not need light.
It could occur in light or in the dark.

我觉得是正确的，dark reaction occur until NADPH & ATP is used up
but light reaction can only occur when there is sunlight.

[ 本帖最后由 Allison 于 3-11-2009 05:17 PM 编辑 ]

darksider

原帖由 bell_25 于 2009/11/3 03:39 PM 发表
哦。。我明白了。。原来gene和codon是不同的东西。。谢谢

我知道Dark reaction is the light independent reaction in photosynthesis..
可是。。我从一本书上看到这个statement。。所以我想问到底 ...

light independent的意思就是不管它白天还是黑夜都会发生.

生物难题

在白天，有光，light reaction & dark reaction 同时进行。
light reaction一定要用到阳光来制造ATP & NADPH给dark reaction.
Dark reaction 的"dark"是指不需要用光，不是指在黑暗中进行。

在晚上，没有光，没有light reaction，没有ATP & NADPH，dark reaction也会停止。大致上plants在晚上没有photosynthesis，只有respiration。

生物难题

原帖由 白羊座aries 于 2-11-2009 02:17 PM 发表
问下ATP synthetase 和 整个oxidative phosphorylation 是怎样操作的?为什么没有oxygen就没有kreb cycle?就因为oxygen是act as final acceptor for oxidative phosphorylation,所以没有O2就没有kreb cycle?没有oxida ...

krebs cycle制造了很多NADH & FADH2，这两个东西会将electrons传给ETC，然后变回NAD+ & FAD。
而ETC会将接收的electron传给oxygen。

没有oxygen，NADH & FADH2就不能将electrons传给ETC，就不能变回NAD+ & FAD。
没有NAD+ & FAD，krebs cycle就不能进行，因为有几个steps in Krebs cycle一定要用到它们。

所以没oxygen，就没ETC，也没Krebs cycle & link reaction (link reaction也要用NAD+)。

虽然glycolysis也要用到NAD+，但是必须记得，没有oxygen，glycolysis也不会停止。
希望能帮到你

[ 本帖最后由 生物难题 于 3-11-2009 08:40 PM 编辑 ]

白羊座aries

原帖由 生物难题 于 3-11-2009 08:39 PM 发表



krebs cycle制造了很多NADH & FADH2，这两个东西会将electrons传给ETC，然后变回NAD+ & FAD。
而ETC会将接收的electron传给oxygen。

没有oxygen，NADH & FADH2就不能将electrons传给ETC，就不能变回NAD+ & ...

完全明白!又简单又容易明白.谢谢,剩下的难题大家已经帮我解决了,其实我想问大家怎样造英文标准正确的句子,但是大家已经帮我解释了,谢谢你们

bell_25

谢谢你们。。我完全明白了。。
感激不尽

darksider

原帖由 bell_25 于 2009/11/3 10:36 PM 发表
谢谢你们。。我完全明白了。。
感激不尽

其实我们所谈的很复杂，也不在于我们的syllabus内。

我之前说的那个有关系到chemiosmosis theory，因为ATP synthetase被regard as complex IV in ETC so in the absence of oxygen, the ion channel would not open and it would not allow the hydrogen ions in the intermembranous channel to pass through it and return to the mitochondrial matrix. Consequently, oxidative phosphorylation which is catalysed by ATP synthetase will not occur (it needs energy released when hydrogen ions pass back into the mitochondrial matrix)

*Complex I, complex III and complex IV in ETCserve as the proton pumps which create proton concentration gradient. Complex I - NADH dehydrogenase , complex III - cytochrome bci complex, complex IV- cytochrome c oxidase and ATP synthetase

---------------------------------------------------------------------------------------------------------------------------------------------------

In the absence of oxygen which accepts four electrons from complex IV(cytochrome c oxidase) in ETC to form water, the electrons will be taken up by NAD+ and FAD+ to form NADH + H(+) and FADH2. In other words, it causes the build up of precursor[NADH + H(+) and FADH2] formed during kreb's cycle. These intermediates inactivate certain enzymes involved in the kreb's cycle （*via allosteric enzyme...not in our syllabus）and so kreb's cycle is halted.

*These molecules, NAD+ and FAD+, become the limiting reagents needed for glucose break down to continue, and when they run out, the TCA cycle stops.

* explain why citric acid cycle is halted in the absence of oxygen.


The NADH + H(+) produced during the absence of oxygen will be used in fermentation(anaerobic respiration) in which pyruvate is reduced to lactate.

pyruvate + NADH + H(+) ------> lactate + NAD+

This NAD+ will then be used in glycolysis to produce  NADH + H+ which is used to reduce pyruvate into lactate.

This explain why even when NAD+ is reduced to NADH + H+ in the absence of oxygen, glcolysis can still occur.

[ 本帖最后由 darksider 于 4-11-2009 02:55 AM 编辑 ]

生物难题

原帖由 bell_25 于 3-11-2009 10:36 PM 发表
谢谢你们。。我完全明白了。。
感激不尽

不客气，有问题尽管问，大家互相交流嘛。。。

白羊座aries

在lineweaver-burk plot , 请问要怎样increase Km value ?

生物难题

原帖由 白羊座aries 于 10-11-2009 10:33 PM 发表
在lineweaver-burk plot , 请问要怎样increase Km value ?

不是很明白你的问题哦。。。。

在competitive inhibition的时候，km就会增加。
所以那个x-intercept (- 1/km) 比起原本的会更加靠近origin。

不知道有回答到你的问题吗？

白羊座aries

原帖由 生物难题 于 10-11-2009 11:54 PM 发表


不是很明白你的问题哦。。。。

在competitive inhibition的时候，km就会增加。
所以那个x-intercept (- 1/km) 比起原本的会更加靠近origin。

不知道有回答到你的问题吗？

故事是这样的,在一个lineaweaver-burk plot里面,x intercept 是指 -1/Km, 比如说 x-intercept 是-2 , 然后x axis 的label是 1/[S] x 10^-3
然后问题是:how to increase the value of Km .

darksider

Anaerobic respiration
If oxygen is unavailable the Kreb’s cycle and electron transfer chain
cannot operate. This is because without oxygen there would be no
way of disposing of the hydrogen at, for example, the end of the
electron transfer chain. However, even in anaerobic conditions,
glycolysis occurs so reduced NAD still forms. If glycolysis is to
continue, the reduced NAD must be reoxidized, that is, the hydrogen
must be removed and disposed of. Anaerobic organisms have
developed two ways of doing this:
1. In yeast, pyruvate is decarboxylated to produce ethenal. Ethenal
then accepts the hydrogen from NAD and forms ethanol. This
releases the NAD to be reused in glycolysis. The conversion of
pyruvic acid to ethanol with the release of carbon dioxide is called
alcoholic fermentation.
2. In mammals, the pyruvate accepts the hydrogen from NAD and
is reduced to lactate. The NAD is then available for further use
in glycolysis. If oxygen later becomes available, the lactate is
reoxidised.
Since anaerobic respiration only involves glycolysis, only the 2 ATP
produced in glycolysis are formed.

bell_25

我又有问题要问。。

Pericardium is a double layer of tough membrane.Is pericardium elastic or inelastic?

谢谢

Allison

Pericardium is elastic
It prevent heart from overstreched due to overfill in blood

bell_25

谢谢。。可是longman的书写inelastic。。
所以我觉得很混淆。。

carly_yen

我觉得好象是INELASTIC....
因为是TOUGH MEMBRANE, SUPPOSE TO BE INELASTIC....
IF IT'S FUNCTION IS TO PREVENT THE HEART FROM THE OVERFILLED WITH BLOOD, 那么如果是ELASTIC的话,不就根本就不能CARRY OUT THIS FUNCTION?

carly_yen

http://books.google.com/books?id ... stic%3F&f=false

读ANATOMY 那一段~

是INELASTIC 的~~~

生物难题

原帖由 bell_25 于 11-11-2009 02:37 PM 发表
我又有问题要问。。

Pericardium is a double layer of tough membrane.Is pericardium elastic or inelastic?

谢谢

我觉得是inelastic，因为这个pericardium是负责prevent overstretching of heart。
如果elastic的话，心脏照样可以overstretch，那pericardium不是多余了吗？