Talk:Citric acid cycle

A simplified view of the process

The simplified view is still too complex for a non chemist to understand. I have an engineering degree with basic chemistry qualification (British O-level), and it makes no immediate sense to me. Why is this an essential process for all living cells? This statement needs to be substantiated in layman's language. — Preceding unsigned comment added by BWernham (talk • contribs) 05:16, 16 September 2011 (UTC)

Why not put "A simplified view of the process" before "Steps"? That's the usual order in explaining something. --Nbauman (talk) 18:13, 26 December 2009 (UTC)

Still.

My problem is that the article seems to say that all Krebs cycles are the same (identical) for all of the Animal Kingdom. That is a shocker. Including ants? Dust mites?

I read that "cats create their own Vitamin C." I know "citric acid." But the writer was intending the information to be unique to cats and this article definitely makes no distinction except for plants. Is that correct? Student7 (talk) 22:40, 16 October 2011 (UTC)

I think I might edit this soon publicly. But for slight clarification here, the process is essential for continuing the breakdown of sugars to molecules usable for energy in the body (Namely ATP, and the NADH that is reduced (generally means activated for use elsewhere to drive other biochemical processes). It should probably should be stated this is the typical biochemical process that directly follows glycolysis. As of the current version though, at least I don't see anything about cats. Newmanrs (talk) 04:49, 27 October 2011 (UTC)

I have made an attempt to simplify the lead as well as put the TCA cycle in better context. Concerning cats, please note that Vitamin C = ascorbic acid ≠ citric acid. Hence the question concerning cats probably is best directed here. Boghog (talk) 18:37, 27 October 2011 (UTC)

What I was hoping for is a declaration or disclaimer about applying to the entire animal kingdom equally as described herein. Student7 (talk) 19:14, 28 October 2011 (UTC)

All aerobic organisms including all animals, all plants, and most bacteria rely on the TCA cycle to generate energy. A basic requirement for life is energy, hence the TCA cycle developed quite early in the evolution of life and was passed on to all organisms that are dependent on oxygen for living. It is no more surprising that all animals use the TCA cycle to generate energy than all animals use DNA to pass on genetic information. Boghog (talk) 20:32, 28 October 2011 (UTC)

After more carefully looking into this (see for example PMID 3332996), it appears that components of the TCA cycle were derived from anaerobic bacteria and the TCA cycle itself may have evolved more than once. However there is intense evolutionary pressure to select the most efficient energy producing pathway and the TCA cycle appears to be the most efficient of the possible alternatives (see PMID 8703096). Hence if several alternatives independently evolved, they all rapidly converged on the currently observed TCA cycle. Boghog (talk) 20:54, 28 October 2011 (UTC)

All present day eukaryotes (including all animals and plants) likely arose from a common prokaryote ancestor. Since the TCA cycle was established in prokaryotes before the appearance of the first eukaryote and since the TCA cycle is the most efficient of the alternatives it is not at all surprising that all eukaryotes use the same TCA cycle. An aerobic organism that used a less efficient energy producing process would be at a severe evolutionary disadvantage in comparison to those did and would need to independently evolve the TCA cycle or become extinct. This is the only possible outcome of evolution. Boghog (talk) 09:25, 29 October 2011 (UTC)

Thanks for your answer on another page. But I still think this needs simpler statement early on for novices that can't make it through whole explanation. Student7 (talk) 00:41, 31 October 2011 (UTC)

I am not certain what you are requesting here. Do you want a simple statement in the lead that all animals (and plants and most bacteria) use the same TCA cycle pathway? I think this is already covered in the first sentence ("a series of chemical reactions which is used by all aerobic living organisms to generate energy"). Or in addition, do you want an explanation for why all aerobic organisms use the same pathway? This second question is more complicated and requires an explanation that the TCA cycle is the most efficient out of several alternatives and therefore there is strong evolutionary pressure to select this pathway. I think it is better to address this question in a separate section after the basics of what the TCA cycle is and why it is important is summarized in the lead. Boghog (talk) 21:52, 31 October 2011 (UTC)

The problem is that the statement: "....used by all aerobic living organisms to generate energy." is wrong. first of all aerobic includes living, so thats just an unneccesary repetition, and secondly, but more important. Its not all aerobic organism, its true for all aerobic eukaryotes. but definetly not for all aerobic prokaryotes. — Preceding unsigned comment added by 130.243.175.103 (talk) 16:34, 15 November 2011 (UTC)

What might be redundant here is "living" since it is implied. Aerobic is certainly not redundant since organisms can be classified either as aerobic or anaerobic. Finally, to the best of my knowledge, all aerobic prokaryotic organisms use the same TCA cycle. Can you name a single example of an aerobic prokaryote that does not use the TCA cycle? Boghog (talk) 20:43, 15 November 2011 (UTC)

Aldol addition vs condensation reaction of citrate synthesis

I've reverted a recent edit by an anon editor claiming that the condensation of oxaloacetate with acetyl-CoA to form citrate is an aldol addition. I think this needs further clarification rather than a hand wave. The majority of the literature (see eg, here here states that it is a (Claisen-type) condensation step. I'm no expert for these types of reactions and perhaps I'm splitting hairs, but this caught my eye, because there seem to be a number of differences between these types of reactions. Malljaja (talk) 17:27, 9 May 2010 (UTC)

Citric Acid

I don't know anything about the topic, but I searched the page for "citric acid", and I couldn't find any mention about what the citric acid cycle has to do with citric acid. I assume it does, and perhaps I could go to the citric acid page, learn the alternative names, cross-reference, and figure it out. But for the uninitiated, I think it would be useful if there was a mention of it. — Preceding unsigned comment added by 76.220.126.134 (talk) 16:27, 16 September 2011 (UTC)

This is called the citric acid cycle as there a molecule of citric acid that is broken down and then regenerated as the cycle runs. If I get around to some edits I may clarify the introductory sections which do appear to be written for and by biologists or biochemists. Newmanrs (talk) 04:53, 27 October 2011 (UTC)

Thanks for clarifying that. The lead now mentions that citric acid is consumed and regenerated during the course of this cycle. Boghog (talk) 10:34, 29 October 2011 (UTC)

Just think of it as orange juice :) 129.180.166.53 (talk) 03:35, 11 June 2012 (UTC)

Actual yield of ATP

Is it 38, 2 net of 40? 36, 2 net of 38? Khan Academy says 38, so we'll stick with that? A lot of Uni's are teaching 36, and I'm pretty sure by optimality, that's wrong 129.180.166.53 (talk) 03:35, 11 June 2012 (UTC)