How Long Does A Water Molecule Last In An Animal

The answer to this, I reckon, is that they don't.

They use molecular oxygen (O₂) dissolved in the h2o for respiration, where it acts equally a terminal electron acceptor, merely as we apply molecular oxygen in the air for respiration. We can speak of the water as being oxygenated.

Water is split in photosynthesis, where reducing equivalents from water are used to reduce NADP⁺ (giving NADPH).

One of the great discoveries of biology, IMO, is that the oxygen formed in green-establish photosynthesis comes from water, not CO₂ .

Tricarboxylic Acid Cycle (Krebs Bicycle) Bluster

Despite claims to the contrary, most infamously by Racker (1976, pp 28 - 29) and Wieser (1980), but also by Madeira (1988) and Mego (1986) for example, h2o is not dissever in the tricarboxylic acid cycle (Krebs Bicycle). Banfalvi (1991) also sails pretty close to the wind on this ane.

That is, reducing equivalents from water are not passed down the respiratory chain, or in whatsoever way used to brand ATP, or are in any fashion a 'source' of energy. Such claims, IMO, are nonsense.

The definitive answers to the Wieser (1980) paper are given past Atkinson (1981) and Herreros & Garcia-Sancho (1981). Both of these manufactures are models of clarity, and categorically refute the claims of Wieser (1980). Nevertheless, as shown by the references in a higher place, the controversy surfaces periodically.

The only sources of reducing equivalents in the TCA bicycle are carbon compounds, and the only electrons passed downwards the respiratory chain are those 'held' in C-H and C-C bonds (Herreros & Garcia-Sancho, 1981). An ionization is neither an oxidation nor a reduction (see Atkinson, 1981) and neither is a hydration. Adding h2o to (say) a double bond does not make the compound any more oxidized or reduced. As far as oxygen and electrons are concerned, and to generalize from a biological point of view, what is has it holds - except in photosynthesis.

As you may have guessed, the splitting of the water in the TCA cycle is a pet rant of mine. Thank you for the opportunity of ambulation my views!

Edit 3

Found this one when searching Google (Brière et al, 2006). In an invited review for the American Journal of Physiology (Jail cell Physiology) at that!

Finally, TCA bike should as well be considered as a h2o-splitting process generating oxygen for acetyl-CoA oxidation [they quote Wieser]

So at present the TCA cycle is producing oxygen from water. Wonders volition never cease!

(end edit)

(end rant)

Edit 2

As rwst and Alan Boyd accept drawn attending to, the concentration of dissolved oxygen in h2o is all important, and varies with (for example) temperature.

In air-saturated buffer at 25^oC the concentration of oxygen (O₂ molecules) is about 0.24 mM (0.24 μmoles/ml, or virtually 0.474 μg-atoms of oxygen per ml). [Chappell (1964)]. This figure decreases with increasing temperature.

Great question, BTW.

References

(Apologies for the incomplete Atkinson and Herreros & Garcia-Sancho references. I have a photocopy of these papers but have been unable to trace the full source. They are both in the 'Letters to the Editor' section of the February 1981 edition of Trends in Biochemical Sciences. They practise not appear to be in Pubmed, or anywhere else on-line. Has anyone ever seen these references quoted, or tin can provide me with a full source?. I'll update if I find annihilation)

• Atkinson, D.E. (1981) TCA Cycle Confusion. Trends in Biochemical Sciences (Feb 1981 edition; full ref to follow)

• Banfalvi,G. (1991) Conversion of Oxidative Energy to Reductive Ability in the Citrate Bicycle. Biochemical Education, 19, 24 - 26 [see here] (pdf plain free to all)

• Brière, J.J., Favier, J, Gimenez-Roqueplo, A.P. & Rustin, P (2006) Tricarboxylic acid cycle dysfunction as a crusade of human diseases and tumor formation. Am J Physiol Cell Physiol, 291, C1114-xx. [Pubmed] [pdf]

• Chappell (1964) The oxidation of citrate, isocitrate and cis-aconitate by isolated mitochondria. Biochem J., 90, 225-237.[pubmed] [pdf]

• Herreros, B. & Garcia-Sancho, J. (1981) TCA Cycle Defoliation. Trends in Biochemical Sciences (February 1981 edition; full ref to follow)

• Madeira, V.K.C. (1988) Stoichiometry of Reducing Equivalents and Splitting of Water in the Citric Acid Wheel. Biochemical Education 16, 94 - 96 [pdf] (plainly free to all.)

• Mego, J.L. (1986) The Role of Water in Glycolysis Biochemical Teaching, 14, 130 - 131. (see here)

• Racker, East. (1976) A New Look at Mechanisms in Bioenergetics. Academic Press, New York.

• Wieser (1980) Textbook Errrors: The splitting of water past the tricarboxylic acid wheel. Textbook mistake or textbook omission? Trends in Biochemical Sciences, 5 (Effect 11), 284. [see hither]. [pdf], apparently gratis to all.

Edit 4

I have not been able to locate the exact reference for the incomplete Atkinson and Herreros & Garcia-Sancho references cited to a higher place merely, in response to this great question, I accept put a copy of a very bad scanned version here

Some other great reference to this controversy which I should accept quoted is the following:

• Losada, Manuel . (1978) Energy-Transducing Redox Systems and the Mechanism of Oxidative Phosphorylation. Bioelectrochemistry and Bioenergetics, 5, 296-310 [Science Directly].

The post-obit is the relevant section, for those who exercise non accept access:

A more than complete version of the Racker reference quoted above by Losada (1978):

Yet, pyruvate has only iv hydrogens to donate to 2 oxygens and with a P:O ratio of 3 should therefore yield only 6 molecules of ATP (Table 1.2). Where are the other 6 hydrogens coming from then that xv ATP tin exist formed? The reply to this question gives us what I remember is the key to the puzzle why nature has designed the circuitous acrobatic scheme of the Krebs cycle. Its major purpose I believe is to increase the energy yield by catalyzing cleavage of water.

There are 3 steps at which water enter the Krebs wheel. - one at the transformation of fumarate to malate an the other two somewhat more than indirectly during the utilization of acetyl-CoA and succinyl-CoA. In the course of the Krebs cycle the hydrogens of these water molecules are separated from oxygen and are donated to DPN or to a flavoprotein (e.g., succinate dehydrogenase) and then transported via the oxidation chain of mitochondria as electrons and protons as we shall hash out later.

[Racker, E. (1976). A New Expect at Mechanisms of Bioenergetics, pp 5-6, Academic Press].

IMO, the final judgement of this quote is complete rubbish. (For DPN, read NAD. DPN, or diphospo-pyridine-nucleotide (or something shut), is an one-time proper noun for NAD)

Source: https://biology.stackexchange.com/questions/3519/do-fish-break-a-water-molecule-to-absorb-oxygen

Posted by: peoplessyrument82.blogspot.com

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