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Process of GTP - ATP


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http://en.wikipedia.org/wiki/Nucleoside-diphosphate_kinase

 

NDK catalyses the transfer of an inorganic phosphate from one nucleoside to another (GTP +ADP -> ATP +GDP) Not quite what you were asking but functionally very similar. The GTP created in the TCA cycle is thus converted to ATP for energy utilisation in cellular respiration.

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Nitpick: GTP itself is a source of energy (the energy is in the phosphate bonds) during translation, for example. Also, cellular respiration is the means to gain energy rather than to utilize it. More precisely, respiration generally refers to the electron transfer reaction resulting in the proton motive force required for the ATP synthase.

 

To avoid (promote?) confusion I should add that most textbooks also include catabolic pathways that deliver reduction equivalents to the electron chain, which IMO is too broad for many purposes.

Edited by CharonY
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There is a good chance that much of it would have been slightly misrepresented, anyway. There has been a slow but continuous shift in perspective with regards to teaching of the material in the last decades. I know that I teach things quite differently now as compared to what I learned as a student.

 

Edit: What I meant is don't feel bad about it in Bio everyone is wrong. Just some less than others....

Edited by CharonY
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Not necessarily I assume that both roughly hold roughly the same amount of energy for most intents and purposes. Usually the GTP is used as a energy source for different purposes than ATP. GTP pools are much lower though. In essence it depends on the context (e.g. total energy calculations?) whether it makes sense to treat them as one. Obviously, the cell does not.

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The phosphate from GTP can be tranferred to ADP creating ATP and GDP by Nucleoside-diphosphate kinase (NDK). NDK can also catalyze the reverse by transferring a phosphate from ATP to GDP creating GTP and ADP. I can't tell you for certain, but the energy stored should be equivalent. ATP and GTP are both nucleosides, differing in their side chains. However, they share the same sugar backbone, and the attached phosphates should be identical chemical bonds, so having the same stored energy. In fact, GTP is a biproduct of the citric acid cycle and often gets converted to ATP and GDP afterwards.

Edited by chadn737
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But again, the pools are regulated differently and it is not a simple unregulated conversion. One of the reasons is that the AMP-ATP ratio is important for intracellular energy regulation. GTP on the other hand is not part of the same circuit. Thus, it can be used without affecting aforementioned ratios.

As already mentioned, in terms of energy content they can be seen as equivalent. Not in terms of physiological role, however.

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But again, the pools are regulated differently and it is not a simple unregulated conversion. One of the reasons is that the AMP-ATP ratio is important for intracellular energy regulation. GTP on the other hand is not part of the same circuit. Thus, it can be used without affecting aforementioned ratios.

As already mentioned, in terms of energy content they can be seen as equivalent. Not in terms of physiological role, however.

 

True, but I never claimed they were equivalent in terms of physiology. NDK however, is essential to maintaining the balance of these pools.

 

EDIT: I would disagree that it can be used without affecting other ratios. There is an equilibrium of GTP and ATP, so depletion of one or the other pool will lead to conversion of one form to the other. Likewise, generation of one or the other will lead to conversion from one form to the other. So changes in the AMP-ATP pool will also affect the amount of GTP, even if indirectly.

Edited by chadn737
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Partially correct. However the GTP pool is usually far below that of ATP (usually one order of magnitude or more) during a wide range of growth rates. Overall the nucleotide equilibria are maintained over quite complex circuits and not just over a single direct pathway (also as a sidenote NDK is quite promiscuous in vitro which complicates matter a bit).

 

There are other regulatory elements that appear to have stronger influence on the GTP and ATP pools. NDK is an important modulator, but it appears more to be a modulator between the pools. The effects of NDK mutants are interestingly more pronounced in pathways involved in nucleotide/DNA synthesis rather than energy metabolism. At least partially this is due to its ability to transfer gamma-phosphates between different di- and triphosphates (rather than exclusively between ATP and GTP). Thus, a mutation alters ratios at various levels kicking a metric ton of regulatory circuits on various levels.

 

Thus mutation affecting ATP synthesis and pools that are related to energy metabolism (PPKs and ppGPP synthesis pathways for example) have a much stronger impact on growth.

 

Or in summary, things are bloody complicated and heck do I have forgotten a lot.

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