Talk:Citric acid cycle/Archive 1

Naming debate

Citric acid cycle is the modern term for the Krebs cycle, almost all modern textbooks now use this terminology. Including the most respected two: Alberts et al. (2002) Molecular Biology of the Cell and Lodish et. al. (2000) Molecular Cell Biology, and one of the more well-known biochem textbooks: Berg, Stryer & Tymoczko (2002) Biochemistry (widely referred to as "Stryer"). You can do a search of all the books via PubMed:

• Citric acid cycle (108 matches in Stryer, 23 in Alberts, 14 in Lodish)
• Krebs cycle (45 matches in Stryer, 8 in Alberts, 9 in Lodish) [Further note: if you click on any of these links, the titles of all the sections use citric acid cycle, and Krebs cycle is normally mentioned only once in the text itself]

--Lexor 09:52, 2 Jan 2004 (UTC)

Lir, The article is written completely using the citric acid cycle terminology, and the bulk of the internal wikilinks go to citric acid cycle. Please use the Talk page here before renaming a page which has had a stable name for a while, agreed upon by most contributors (see the discussion above), has many links to that page, and which is already internally consistent with that name. If you do rename, then you also need to take on the responsibility of ensuring no double redirects, which hasn't been done. --Lexor 10:03, 2 Jan 2004 (UTC)

My book is from 2003, making it more recent than your sources. Mine uses Krebs cycle. With more than one "technical name" in use, Krebs seems to be the best compromise. In addition, Krebs cycle gets far more hits on yahoo!; we have a naming convention to use whatever is most commonly used. Lirath Q. Pynnor

But what 2003 book are you using? The references I cited are pretty much the gold standards in molecular, cell biology and biochem. As far as the Wikipedia:Google Test goes, it's not so clear: Krebs cycle gets 30,000 and citric acid cycle (CAC) gets 21,000, which means that there is quite a deal of support for CAC. The Google (or Yahoo) test shouldn't be used blindly either, it's just one data point. As I pointed out in the Talk:Cell biology discussion, I used the Google test as one data point amongst many including: notable gold standard texts, journals names, organization names, and the currently accepted/recommended terminology in the field in question.

Finally if the vote goes to change the page to Krebs cycle, you will need to change all CAC references to "Krebs cycle", and fix all redirects. --Lexor 23:47, 2 Jan 2004 (UTC)

No acids in the cycle

There are no acids in the cycle, so why do you choose to name it the "tricarboxylic acid cycle"? Just look at the diagram —Preceding unsigned comment added by 163.1.143.161 (talk) 22:06, 19 January 2009 (UTC)

Poll

Krebs cycle (Google:31,400) or Citric acid cycle (Google:21,300)?

• Krebs

1. Lir (this is what my textbooks use)
2. The Fellowship of the Troll - it always was the Krebs cycle when I was at school (admitedly, back in the day) although it could be a UK/US thing?
3. Oliver P. 06:56, 7 Jan 2004 (UTC)]]
4. Guillermo3 01:18, 12 Jan 2004 (UTC)
5. →Raul654: Had my mom (a biology teacher) look it up in Campbell's textbook, which is considered to be one of the leaders on the field. It uses Krebs. (What was the year of publication?[168...] --- 5th edition, 1999 →Raul654) (Aha, that's the same book I use...... I have 6th edition, 2002, and that also refers to it solely as the Krebs cycle... see at the very bottom of this page ugen64 23:24, Feb 4, 2004 (UTC))
6. I was told Krebs cycle at school. Secretlondon 07:31, Jan 18, 2004 (UTC)
7. Krebs cycle at school, again... ugen64 23:24, Feb 4, 2004 (UTC)
8. Krebs; it's what my chemistry friends use. James F. (talk) 05:39, 13 Feb 2004 (UTC)
9. jollyshortfellow (I'm a freshman in high school, CA, and my textbook says the Krebs cycle, which was named after the German scientist Hans Krebs. However, my teacher says that either way is ok, since citric acid cycle is used in higher levels of biology.)
10. Doing Biology at Oxfird University (England). We were tought Kreb's, because it is Citrate. 87.80.242.28 (talk · contribs)

    I don't understand this rationale. In a cell, citrate is in its ionic form (citric acid). Is Oxfird a typo for Oxford? I hope not as they should know better than to teach those types of misconception. David D. (Talk) 19:35, 6 June 2006 (UTC)

    Er, the ionic form is citrate. Acid is the protonated form. But the "Oxfird" guy is voting for "Kreb's", not Krebs; though he probably "was tought" it at a speeling school. 218.102.71.167 03:18, 20 June 2006 (UTC)

11. Okay, so I'm only studying biology at A-Level, but we're taught that it's called Krebs cycle. Matisia 22:16, 4 October 2007 (UTC)

• Citric acid cycle

1. Lexor (used by Alberts et al. 2002, Lodish et al. 2000, Stryer et al. 2002, see section above for full references)
2. Maximus Rex (this is what my textbooks use ["Organic Chemistry" by John McMurry, 5th edition, 2000])
3. Leave well-enough alone. Peak 09:23, 4 Jan 2004 (UTC)
4. Citric acid cycle is more clear. --mav 01:24, 7 Jan 2004 (UTC)
5. Citic acid cycle is more de-personalized. What if 10 years later Krebs' discovery was found to be a result of other scientists' works? 大将军, 都督中外诸军事 (talk) 01:44, 7 Jan 2004 (UTC)
6. Kokiri (went to scirus for the following: CAC 11,281 results (4942 journal); KC 8779 (2090) and Tricarboxylic Acid Cycle 5534 (2371); always knew it as the the CAC; alternatively call it Krebs CAC - I've seen that too)
7. Ryan_Cable
8. tb - This is what i've heard it's called nowadays. I think there must have been, at some point, a move away from naming cycles/disorders/etc after discoverers and researchers, as a surname gives little idea of what the cycle is about. Maybe they should rename Phillips screwdrivers too. :-)
9. 168... 01:14, 19 Jan 2004 (UTC) I think this is how it's taught nowadays, and so how it should be taught here. Nothing wrong with an " (a.k.a. Krebs cycle after Hans Adolf Krebs)" in the first line though.
10. UtherSRG - 168... Has it on the nose. Let's modernize!
11. Citric acid seems likely to be far better recognised than krebs as an identifier for this cycle. Not as the name but just because citric acid itself is better known, so people are more likely to recognise what is involved. Krebs definitely needs a mention and a redirect from Krebs cycle to here is needed as well. Jamesday 04:35, 22 Jan 2004 (UTC)
12. MykReeve - CAC more consistent with current teaching. 09:30, 25 Jan 2004 (UTC)
13. Ruhrjung 13:31, 23 Feb 2004 (UTC) - most suitable in an international context
14. Rich0 - While I always think of it as being the Krebs Cycle myself, I'd stick with the status quo, especially since it seems like the textbooks seem to be moving in this direction. I've had professors who've used each of the common terms, and none really stood out that well.
15. GAThrawn22 03:51, 19 October 2006 (UTC) - Used by Principles of Biochemistry (Lehninger). I think that the scientific community is moving away from calling it the Kreb's cycle. I think that a redirect and a brief explanation in the beginning of the article is sufficient. My experience, is that the scientific community has been moving away from anything named after people and are attempting to come up with standard or simpler terminologies.

On the pointlessness of polls

Why do we keep having these polls about what rules to apply to individual articles? Surely everyone recognises that consistency is good, and that we should have a single policy on naming conventions that applies equally to all articles, yes? We have a policy here which says to use the most common names for things except when that name is "misleading" (not the case here) or "unreasonably offensive to large groups of people" (also not the case here). It doesn't say to use the most modern term, and it doesn't say to use the term used by the most highly respected professionals. It just says to use the most common term. If anyone wants to change the policy, they should take it up on the policy's talk page. Until the policy is changed (and on the basis of this, it looks like it might be), we should apply it to all articles equally, and not make arbitrary exceptions for whichever articles happen to have polls on their talk pages.

The Google search suggests that "Krebs cycle" is more commonly used. It's possible that the Google search results are skewed in some way, and that really more people use "citric acid cycle". But that would need to be argued. Anyway, is anyone even claiming that? If not, then "Krebs cycle" is what we should be using, regardless of the outcome of this poll. -- Oliver P. 06:56, 7 Jan 2004 (UTC)

The Wikipedia:Google Test should be but one data point. I have argued (see above) that citric acid cycle is the current standard usage, especially so in current textbooks etc. Also Krebs cycle doesn' "win" by an order of magnitude, it's a 3:2 ratio which doesn't make it win "hands-down". I think blindly applying the policy on the basis of Google ranking would be a bad thing. This is not an "arbitrary exception" either because these discussions tend to arise for articles for which there are good reasons for their being a discussion, for many people I think citric acid cycle is the most common term. I think the Google test doesn't clinch it one way or the other, so having a discussion is a valuable thing. --Lexor 21:34, 7 Jan 2004 (UTC)

Okay, let's drop the talk about Google for now. I admit that the results of a Google test may not be an accurate reflection of real-life usage, for a number of reasons. And I admit that since the ratio is only 3:2 in favour of "Krebs cycle", my arguing this point might seem rather petty. However, there does seem to be a fundamental difference of opinion on what policy Wikipedia should use on naming pages, and that needs to be addressed.

You are arguing that "citric acid cycle" is the current standard usage (used in modern publications and so on); I am arguing that "Krebs cycle" is the most common usage (in minds of the world's populace as a whole). The two propositions are not mutually exclusive, and may well both be true. Suppose, for the sake of argument, that they are both true. Now which title should we use? Should we title pages according to current standard usage or most common usage? If we title this page according to current standards, and others according to common usage, then we are making an arbitrary exception. Why should we title this page according to current standards, and not others? If you think that we should do the same for all pages, then the policy needs to be changed. If you don't think that we should do the same for all pages, then you need to explain why you think this page is a special case. -- Oliver P. 07:39, 11 Jan 2004 (UTC)

I assume we mean "standard" in sense 2 of the American Heritage Dictionary

1. Serving as or conforming to a standard of measurement or value. 2. Widely recognized or employed as a model of authority or excellence: a standard reference work. 3. Acceptable but of less than top quality: a standard grade of beef. 4. Normal, familiar, or usual: the standard excuse. 5. Commonly used or supplied: standard car equipment.

Given that, I think the answer to your question is obviously we go by the current standard. You could argue that common usage should be designated the standard, but if you concede that another usage is standard, than you should agree to go by that one...or back up and choose another word than "standard."168... 03:06, 21 Jan 2004 (UTC)

Yes, the word "standard" is ambiguous, and perhaps my use of it above wasn't entirely clear. When I said that the term "citric acid cycle" might well be the "current standard", I meant that it may well be the term most commonly used in the latest chemistry textbooks, which is what people seemed to be arguing about. However, I am arguing that the question of what the current standard is is irrelevant to how we should name this page. Our naming convention (the Wikipedia standard, if you like) is to use the most common name. Given that most people haven't bought the latest chemistry textbooks, it is not necessarily the case that the term most familiar to the general public will be the one that is currently being pushed by the textbook writers. And see below... -- Oliver P. 02:56, 26 Jan 2004 (UTC)

You certainly haven't convinced me that CAC is the current usage in textbooks. Im sure textbooks use it, but listing a couple of yours hardly proves your case. Lirath Q. Pynnor

I haven't done an exhaustive search on all textbooks, you are correct. But I have cited three key textbooks that are used in at least one biochemistry, molecular biology or cell biology course in a significant percentage of English-speaking universities in the world. Alberts et al. is probably the most highly regarded molecular biology textbook in the world, of course, it doesn't always mean it is "right" all the time, but it does reflect and set standards in molecular biology terminology in the same way that the Oxford English Dictionary does for language. You have still not told me which text you are using. --Lexor 10:14, 9 Jan 2004 (UTC)

It doesn't matter what book I have, there are lots of books and obviously Krebs cycle is used, your referring to so-called "key" textbooks does nothing to indicate what the common usage is. Lirath Q. Pynnor

Granted it may not absolutely indicate common usage, but given the widespread use of these three textbooks in a large chunk of the English speaking world it may indicate the direction. In the absence of a complete survey of all textbooks, it's still an important data point. Could you please humour me and tell me which textbook you are referring to? That way we would have at least 5 books as data points: my 3, Organic Chemistry by Murray (which Maximus Rex lists) and your book. I'm genuinely curious to know which books still use the Krebs cycle terminology. --Lexor 12:11, 9 Jan 2004 (UTC)

My 2 cents

Both 'Citric acid cycle' and 'Krebs cycle' are correct. I was taught it is the 'Krebs cycle' both in high school and in my lower division biology courses. My upper division courses and instructors, however, tended to use 'citric acid cycle' more often and that usage seems to becoming more common. I have nothing more to say other than that and would be happy with either title. Wouldn't it better to direct all the time and effort put into this discussion into actually expanding this article? --mav 11:09, 10 Jan 2004 (UTC)

[Peak:] Yes, that's why I voted to keep it as it is, but you haven't recorded a vote so far as I can see. Peak 05:11, 12 Jan 2004 (UTC)

Mav's vote was recorded above to keep title as citric acid cycle. I also agree that we could better spend our time improving the article, which is why I was suggesting that we keep the article the status quo in the first place. --Lexor 08:30, 13 Jan 2004 (UTC)

I think Krebs deserves some credit for his work. Lirath Q. Pynnor

[Peak:] I'm sure we're all agreed that Krebs deserves full credit for his work. But that cab best be addressed in the article itself; please also note that no-one has suggested that there shouldn't be a REDIRECT from 'Krebs cycle', as there is now.Peak 05:11, 12 Jan 2004 (UTC)

And I think it can best be addressed by referring to this as the Krebs cycle, like most of the people on the internet do. Lirath Q. Pynnor

Can we just leave things as they are Lir, please? The vote looks to swing to the status quo of citric acid cycle. The vote request has been listed for a while right now, and I think it's fair to say that the status quo is upheld. If we did change it, then the article should refer to consistent terminology throughout, and all CAC -> Krebs cyle (and all links would need to be fixed, there are far more links to citric acid cycle than Krebs cycle, and all broken double redirects would also need to be fixed). Rather than do all that: let's just leave the article with the current name. We can tinker with the intro sentence to award Krebs as much credit as is needed. --Lexor 08:30, 13 Jan 2004 (UTC)

Perhaps you missed my question above, Lexor. Should we title pages according to current standard usage or most common usage? You admit above that the present title "may not absolutely indicate common usage", so presumably you're arguing for the former (as is 168...). However, our naming convention says to go for the latter. The poll would seem to indicate that there is a lot of opposition to the convention, but maybe the people who have contributed here aren't representative of the Wikipedia community as a whole. As I said above, rather than debating each page in turn, and ending up applying different conventions to each page, we should discuss the general policy (on the policy's talk page), and then apply whatever is agreed to all pages uniformly. -- Oliver P. 02:56, 26 Jan 2004 (UTC)

I think you are misreading the naming conventions. For example, there's this section...

"Don't Overdo it

"In cases where the common name of a subject is misleading (For example: "tidal wave" would be a misleading title since these phenomena have nothing to do with tides), then it is sometimes reasonable to fall back on a well-accepted alternative (tsunami, for example)."

I guess one could argue that the analogy with the case we're discussing isn't perfect, but "tsunami" strikes me as a cognoscenti's term, and so is something like the "current standard" in our scenario. I think most of that policy page is about deciding what to do in the absence of text books defining the standard. When a "current standard" exists, it seems to me from the "tsunami" example that the policy is to use the current standard. This is just common sense. Wikipedia is not trying to refashion established academic disciplines. What people come to an encyclopedia for is a summary of accepted scholarship, not pop wisdom or original scholarship that's never been peer reviewed or published elsewhere.168... 04:49, 26 Jan 2004 (UTC)

I think you're misunderstanding the "tidal wave" example. It is brought up as an example of a misleading title. It is explained as follows: '"tidal wave" would be a misleading title since these phenomena have nothing to do with tides'. (I think this is a ludicrous argument, incidentally. But that's an argument for another day.) Academic standards aren't mentioned. Nowhere on the page is there even a hint that the policy is about "what to do in the absence of text books defining the standard". If the policy was to use academic text books first, it would say so! No-one is suggesting any of the other things you mention ("refashion[ing] established academic disciplines", "pop wisdom", or "original scholarship"), so I don't know why you bring those up. The article body should contain a summary of accepted scholarship, of course; the title is little more than a way of finding the article, and this should be made as easy as possible for the readers - i.e. the general public, not the academic community. Anyway, I've brought this matter up on the relevant talk page, so we should continue this discussion there. -- Oliver P. 06:53, 26 Jan 2004 (UTC)

"Tsunami" does not embody the principle of "easy as possible for the readers," most of whom almost certainly say "tidal wave." Given that the policy page considers tsunami examplary in the context of "Don't Overdo it," I believe the policy is that the appropriate title is not always the word or phrase most popularly associated with the topic of the article. We'll have to agree to disagree about the pertinence of "refashioning," etc. Titles are part of scholarship as far as I'm concerned.168... 07:08, 26 Jan 2004 (UTC)

Not about new vs old - Biology vs Chemistry

• I'm told that it's not about Krebs cycle being the old accepted term and CAC being the new term. My girlfriend (biologist) told me that's it's more about your area. Krebs has always been used by biologists. In recent years, however, chemists started referring to it instead as CAC and TCAC. But biologists still call it Krebs. →Raul654 09:20, Feb 10, 2004 (UTC)

• I think thats just more reason to change the name to Krebs, the "common" person coming to view this page will probably not be a chemist -- they will probably, at most, only be familiar with the topic from having read about it in a biology class. Lirath Q. Pynnor

• All comes from the facts that it's easier to say "Krebs cycle" than to say "CAC" or even "TCAC" plus it is esier for the kids (and the classical biologists too, such as Raul654's girlfriend) to remember the name of the cycle by remembering the name of the guy who has discover it, than remembering some dry chemical abreviations. On the other hand it's easier to write "CAC" or "TCAC" than "Krebs cycle". So, i say the written form should be "TCAC - tricarboxylic acid cycle" (and this is how i reffer to it in any text i write in Wikipedia) this form is better than "CAC", because it reflects that another tricarboxylix acid - isocitrate - is involved. And the spoken? Well it's up to you. BorisTM 09:05, 21 October 2005 (UTC)

• It seems unlikely that there will be more people coming here who have studied biological chemistry then chemistry. Regardless, it's mentioned earlier that several of the leading textbooks on the biology side have switched to citric acid cycle, so it seems that this may be a generational shift, with older readers using krebs and newer citric acid. Jamesday 22:08, 16 Feb 2004 (UTC)

• Its claimed earlier that several of the leading textbooks on the biology side have switched to CAC -- its hardly proven, several other users have documented the opposite phenomenon -- in short, the only way to tell which is more common is via google/yahoo; where its clear that Krebs is more common.
  It may seem unlikely that more people coming here will have studied chemistry, rather than biological chemistry -- however, the Krebs cycle is covered in basic freshman level biology courses -- it is not mentioned in the equivalent level of chemistry course. Lirath Q. Pynnor

• When I took freshman bio in high school, we called it the Krebs cycle. Then I took two years of high school chem, and we didn't call it anything, because we didn't discuss it. I don't know what criteria you want to use, but I'm pretty sure "Krebs cycle" is the name people know. My two cents. Isomorphic 19:21, 24 Feb 2004 (UTC)

• Yeah, you are kinda right. But see that's because of the chemestry level they teach you in high scholl. There you don't study about Fe-S clusters and their role in the reaction mechanism of Aconitase family of enzymes (ACO1, ACO2 - see the the picture in the article). As a science field chemistry is up higher in the hierarchy than biochemistry is. If chemistry is one circle and biology is another where this two circles overlap lies biochemistry. BorisTM 09:05, 21 October 2005 (UTC)

• Yeah, think about it. Why would chemistry students discuss the citric acid/Krebs cycle for any reason? Biochemistry's a different subject altogether, anyway... ugen64 15:21, Mar 7, 2004 (UTC)

• Because it's about chemical reactions, after all. Yeah, the conditions are different, but still you have braking of chemical bonds. BorisTM 09:05, 21 October 2005 (UTC)

straight to the point

I need help---my "hippy", I say this endearingly, friend said citric acid is bad for you--209.165.44.104 07:19, 24 Apr 2004 (UTC) but as a scientist by nature I know it is naturally in everything. Christine

---

The citric acid cycle is not bad for you. It is simply a mechanism for breaking down fuel molecules (ie. sugar) and providing ATP (energy). Bensaccount 22:55, 29 Apr 2004 (UTC)

No, she was asking if citric acid in general is bad for you, methinks. It's not good for you if you drink it straight, but yes, it's found in many citrus fruits and naturally in most animals as a part of the citric acid cycle. It's not bad for you, unless you decide to drink 100% citric acid or something... ugen64 17:14, May 9, 2004 (UTC)

Have you shown your hippy friend the the citric acid article?

FADH

According to the "7th" reaction of the CAC: VII. Succinate 7. Succinate dehydrogenase Oxidation FAD FADH2 In other words succinate is converted to fumarate by succinate dehydrogenase (SDH). This is an oxidation reaction. Up until this point everything is fine. But I take issue with the other reactants (FAD) and products (FADH) of the reaction. FADH2 is not the final product of the ancillary reaction, and it is better to refer to FAD as a cofactor. As noted in the img. FAD is inserted into SDH. From my understanding FADH2 will be oxidized back into FAD by Q (quinone). This produces FAD (the starting cofactor), and QH2 (what I propose to be the final reactant). The exact mechanism of the reaction can be found on the Succinate—coenzyme Q reductase (another name for SDH), and it involves the transfer of electrons from FADH2 to an iron-sulfur group, to a heme group and finally to QH2. QH2 will always be produced after the oxidation of succinate to dehydrogenase and will be relleased into the membrane (unliked FAD which is stuck to the enzyme. The reason that most textbooks describe the final product of the reaction to be FADH is historical, and it does not accurately reflect the events that take place inside the cell. Therefore I propose the following change of the "7th" reaction: VII. Succinate 7. Succinate dehydrogenase Oxidation QH QH2 Also, the image will need to be changed. Perhaps showing FAD as a catalyst rather than a product.

>> I would agree, as my copy of Principles of Biochemistry (Horton et al.) has that down. Even better, my professor, Larry Moran (who incidentally was the principal author of the textbook I just mentioned) explained why. For one, FAD/FADH2 are usually prosthetic groups, and is no different in this case. Thus, FAD/FADH2 cannot diffuse about, unlike quinone. All the best, Alingus 04:10, 15 March 2007 (UTC)

I changed that FADH2 to QH2 in the table. It's one enzyme after all, it is only confusing to split the reaction of the enzyme into two parts - stopping at an intermediate state of the enzyme - and watch the shortlived FADH2 as the endpoint of the citric acid cycle. I saw Malljaja didn't like my attempt (I admit the result was so-and-so, and it's true GTP is used directly as an energy source in some reactions) to make the overview text match the table, hopefully it is better now. I tried to make the text easy on anyone who see FADH2 as a key intermediate. Narayanese 15:25, 5 November 2007 (UTC)

Simplifying the FADH2 issue that way is indeed reasonable, but the problem with that is that technically the step to QH2 rather belongs to the electron transfer chain. It also seems to run contrary to the summary given in textbooks, so the entry may become unstable if QH2 was included, as editors may stumble over it. I'm not going to lose sleep over it so long that the relationship of QH2 with TCA and oxidative phosphorylation is made clear. Thanks. Malljaja 16:52, 5 November 2007 (UTC)

I like your expanding edit to the overview text before the table. But ATP is not only generated enzymatically, there is also a separate enzyme (EC 6.2.1.5) catalyzing the same reaction (succinyl-CoA -> succinate) but producing ATP from ADP instead of GTP from GDP. As far as I can understand it is in all organsims. Biochemistry & Molecular biology of plants by Buchanan, Gruissem, Jones shows an ATP being produced in plant, but I see an entry in UniProt for a GTP-producing rice succinyl-CoA synthetase. Humans at least have both (see http://www.expasy.org/uniprot/Q9P2R7 and http://www.expasy.org/uniprot/P53597), and Biochemistry, Berg et al mentions in passing that both exist (page 476). I don't know the difference between the roles of the two, if any, but I remember reading an article somewhere speculating that the GTP-forming variant is for the reverse reaction. But nucleoside-diphosphate kinase is worth a mention in the article, perhaps not in the table. Narayanese 17:24, 5 November 2007 (UTC)

It wouldn't be the first time that the newer literature contradicts the textbooks--it's certainly possible that different organisms (plants, fungi, etc) have slight or even gross deviations from the "common" TCA cycle sequence and metabolites. I'm not sure I understand your second sentence though--both rxns are enzymatic, the example you give (for EC 6.2.1.5) and the conversion of GTP to ATP by NDK. If you can source the info for EC 6.2.1.5 (also that it exists in all organisms, or at least the one for which it's been functionally/mechanistically shown) it should surely be in there (if not in the table than in the text). Is EC 6.2.1.5 a committed TCA cycle enzyme or is it also active elsewhere? I'll also try to have a look, but am swamped right now. Malljaja 19:02, 5 November 2007 (UTC)

Diagram

I made a diagram, hope you guys like it. I think it looks good, better than other pathway diagrams I have made. It's in SVG, I hate SVG. SVG always messes with my designs, but it is fairly clean. So anyways, feel free to edit if you'd like (be kind) or just ask me to fix/change something. I think it is all right. I used the reaction that the article mentions (ie I included aconitate and oxalosuccinate). I was playing with the idea of putting a little circle with a number inside at each reaction arrow, the numbers would be labels for the enzymes (jeesh that was a bad sentance). Adenosine | Talk 08:07, 2 October 2006 (UTC)

Well I just looked at the italian version of this page, and it's great! Their diagram is tight; we each had different focuses, but their's is very effective! Um, I'm suprised nobody hasn't just vultured that picture and translated it?! But what can you do? They have little numbers on their arrows, I like it, should I do the same on our page? What about the arrows that show where the molecules can go (eg to amino acid synthesis etc.), would that just be too much!? Adenosine | Talk 08:12, 2 October 2006 (UTC)

I really like the Italian version: even the yellow shading contributes to the overall readability of it. The arrows, especially, I think are vital. Also, we should especially "borrow" their little "metabolism" navbox. – ClockworkSoul 11:57, 6 October 2006 (UTC)

Cleanup Tag

I realize you guys are maybe still arguing about what needs to be done, but this really needs a cleanup tag until you figure it out.

Notes, briefly:

• The overview says this produces ATP, but the rxn equation claims GTP.
• Even if you guys can't agree on what to call it, just change all of the names for now so that they're consistent. I suggest citric acid cycle, because it is more descriptive of the reaction and less of the history behind its discovery.
• The part of the page with the tables is very difficult to read and I'm not immediately clear what the table is attempting to show. Perhaps if it could be standardized so that it resembles the glycolysis page?

--aciel 01:52, 2 November 2006 (UTC)

---

Austailan 1.9 cents worth.

How about you have 2 articles, both exactly the same except one is Titled Kreb's cycle and the other is titled The Citric Acid Cycle?

If you searched for CAC it would direct you to CAC if you searched for Kreb's it would direct you to Kreb's. If this is possible please do so. Then expand it, I have a Metabolism exam on monday and this is a very useful resource!

--The Problem with 2 articles is that it would be redundant and unnecessary. The Citric Acid Cycle is the 'proper' name for the Krebs' Cycle. DWolf2k2 15:43, 2 April 2007 (UTC)

Tuppence worth from the United Kingdom.

Although I can't obviously speak for the entire population of the U.K., from my experience we use the term Kreb's cycle (If at all mentioned in a text, 'citric acid cycle' will usually be in brackets).

Matisia 22:12, 4 October 2007 (UTC)

Image not representative

There are a couple of problems with this image. It's cis-aconitate, not cis-acotinate It's α-ketoglutarate, not a-cetoglutarate. Ravenshelix 22:55, 12 October 2007 (UTC)

Very detailed, but what does it all mean?

The last time I had the Krebs cycle described to me, it involved the use of B vitamins to extract energy from nutrients. With all of the five and six syllable chemical names listed here, the actual inputs of the process are completely obscured. Could someone do something to connect this whole mess to something that you don't need a college degree in chemistry to understand? Robert Rapplean 17:46, 30 October 2007 (UTC)

Szent-Györgyi-Krebs cycle

Why are we adding this as an alternate name for the TCA cycle? I have never heard it called this and I think having it in the lead will cause confusion. If we really want to keep this information it should be in a history section. David D. (Talk) 05:56, 7 November 2007 (UTC)

Alright I just made this edit to try and clean up the lead. Three names is more than enough, I suggest it gets too confusing to have a rarely used fourth name too. David D. (Talk) 06:04, 7 November 2007 (UTC)

I'd like to differ--Albert Szent Györgyi had done groundbreaking work on the Krebs cycle, see for example [1]. Groundbreaking work is often ignored in Science (as it so often goes against the grain of "common" knowledge), and the praise is almost universally heaped on researchers doing the later (and often easier) and loftier work of "polishing" and are most vocal about their accomplishment(Kary Mullis may be such an example). I'm not begrudging Hans Krebs' contribution, and I too am most familiar with the cycle under its name, but I think that Szent Györgyi should be included in the lead. Malljaja 11:32, 7 November 2007 (UTC)

I'm not try to ignore his work but the reality is that Szent-Gyorgyi name for the TCA cycle is never used except by his biographers and direct collegues. Far better would be a history section to put his contributions into perspective. David D. (Talk) 12:22, 7 November 2007 (UTC)

I've been perhaps a little unclear--I'm not actually suggesting to use the Szent Györgyi name asan alternative name for TCA/Krebs, but to include a brief mention of him in the lead (because a history section has yet to develop, usually languishes at the very end, and, I suspect, isn't read by many). Thanks. Malljaja 13:47, 7 November 2007 (UTC)

I see no problem with that. I aways read the history section for perspective. If done well it is the best part of the article. The one here has a lot of potential since the linear to cyclic breakthrough can be documented as well as the confusion from scientists at the time why the 4C molecules could increase respiration of pyruvate to CO2 without actually being used up. Not to mention Krebs nove from Germany. David D. (Talk) 14:05, 7 November 2007 (UTC)

Hello! It is a big shame that someone remowed the "Szent-Györgyi-Krebs cycle" name and added it to the and of the article like something crap.... why didn't you removed the other names too? You dont know this name ok, but this doesnt mean that it doesnt exists... yes I know that it is hard to spell it...

I think his name should be mentioned in the begining... —Preceding unsigned comment added by Baxter9 (talk • contribs) 15:07, 7 December 2007 (UTC)

Did you read the first paragraph? Are you saying you have heard the usage of the Szent-Györgyi-Krebs cycle? David D. (Talk) 15:18, 7 December 2007 (UTC)

Yes, it is in use. For example: "The citric acid circle and the Szent-György cycle in pigeon breast muscle. Biochemical Journal, London, 1940, 34: 775-779." (I heard it many times...) but most of the time people only say Krebs cycle because this is the shorter one.

Also, this is an encyclopedia so every useful information should be mentioned. Baxter9 (talk

A 1940 paper qualifies as in use? I have no problem if you want to write a section on the history of the TCA cycle. In that context this is relevant but to say the Szent-György cycle or Szent-György-Krebs cycle name is in use is not reality. David D. (Talk) 23:03, 7 December 2007 (UTC)

http://www.jbc.org/cgi/reprint/146/2/503.pdf from 2007. —Preceding unsigned comment added by Baxter9 (talk • contribs) 16:45, 8 December 2007 (UTC)

From 2007? Did you even read it? David D. (Talk) 22:35, 8 December 2007 (UTC)

I doubt the reader has any use of learning a name that never caught on (zero hits on PubMed)... anyone who has heard the name Szent-György-Krebs cycle will understand the name Krebs cycle, so mentioning Szent-György in the lead is no help. Make a history section if you like attributing discoveries to their researchers. Narayanese (talk) 21:16, 8 December 2007 (UTC)

Energy charge as regulator

I'm not sure I agree with the following edit saying that ATP (although we should consider ADP and AMP too) has no allosteric role in regulating flux through the TCA cycle. Don't most text books have the energy charge regulating pyruvate dehydrogenase and isocitrate dehydrogenase? David D. (Talk) 05:04, 20 November 2007 (UTC)

That was at least how they thought in the 70s, I can't find anything about how they think nowadays, the newer papers I read only said that ATP competes with CoA, and one speculated that the binding of ATP to various non-ligase enzymes is just a sideeffect of how the adenine nucleotide binding pocket has been reused for evolving binding sites for CoA and other adeninosine-containing coenzymes. So GraybeardBiochemist could be right. Narayanese (talk) 11:02, 21 November 2007 (UTC)

Possibly, I'm not sure if he was considering ATP alone or energy charge. Obviously AMP may be changing much more than ATP, although I have no idea what the figures are. Also the cite is for a general text book, i did a quick search in the literture but I did not find anything obvious. Its a hard search to hit the target and I probably didn't have my keywords refined well enough. David D. (Talk) 14:56, 21 November 2007 (UTC)

Quick Suggestion about the Diagram

Some of the steps of TCA cycle are reversible as many of you know: citrate to isocitrate, succinyl-coa to succinate, fumarate to malate, and malate to oxaloacetate. I'm not sure if the image could be easily updated but if arrows pointing in both directions could replace the single direction arrows for those reversible steps I think it would improve the diagram.

Another small suggestion, I believe the the structures cis-Aconitate and Oxalosuccinate are considered intermediates and are not present in many diagrams. While I praise this diagram for showing them I think it could be important to denote them as intermediates in some way, most organic chemistry texts denote intermediates by placing the structure inbetween 2 large brackets []. Mikesot (talk) 05:05, 5 March 2008 (UTC)

I'll try doing some changes, removing the intermediaries and replacing FAD/FADH2 by Q/QH2 at the same time. I think intermediaries belong in the text, not in the picture. Narayanese (talk) 14:22, 15 March 2008 (UTC)

File:Citric acid cycle noi.GIF

I have a bit problem figuring out how malate to oxaloacetate is reversible but not some of the others (also 30 kJ/mol). Narayanese (talk) 15:26, 15 March 2008 (UTC)

Naming question

Why do we use a name that suggests that carboxylic acids are involved? All the intermediates are deprotonated, and hence, not acids. ---- —Preceding unsigned comment added by 129.67.21.28 (talk) 14:02, 28 April 2008 (UTC)

• That's a fair question. Perhaps it's a better-sounding name than "citrate cycle"? – ClockworkSoul 14:06, 28 April 2008 (UTC)

cis-aconitase in lead image

(Reply to User talk:Narayanese#Citric Acid Cycle) cis-Aconitase is pretty much only an in-enzyme intermediate (the only other function is as precursor to itaconate), so I think it would be but a diversion in the picture for the compounds that are not enzyme intermediate. The links to enzyme pages should be enough for those interested in the mechanisms and intermediatry compounds of the CAC enzymes. Narayanese (talk) 20:21, 13 June 2008 (UTC)

And why was the lead picture replaced by a factually inaccurate pic? I you really want the intermediary compounds I guess I could readd them insome form to the jpg, even though I think the picture is better off without them. Narayanese (talk) 20:59, 30 June 2008 (UTC)

Blank header

When people create these articles, like someone said below, please keep in mind that the people who come seeking to learn about this subject do not have a masters in bio chemistry. If they did, they wouldn't need the article that much. Majority of people who use an article like this are students who need a clear definition to start with. This would have been so much easier for me if the introduction said something along the lines of. "The Citric Acid Cycle is a series of enzyme-catalyzed chemical reactions of importance in living cells that occurs in the mitochondria. This cycle produces ATP (cell energy). Instead, I had to do another 20mins looking up what the hell this cycle actually does (end product), wich is more important than all the steps that take place. I know you sound really smart spouting all of that off, but please use common sense. lol please forgive my assininess

--Johnny Nesbit —Preceding undated comment was added at 08:38, 19 September 2008 (UTC).

---

—Preceding unsigned comment added by Jrnesbit (talk • contribs) 08:36, 19 September 2008 (UTC)

Well, the lead says "The citric acid cycle [...] is a series of enzyme-catalysed chemical reactions [...] in the matrix of the mitochondrion [...] to generate a form of usable energy." Plus you have a products table that states what goes in and what goes out. Are you asking for a reorganisation of the lead, or...? Perhaps you were fooled by the name of the overview section (it's not an overview but an in-depth step-by-step description). Narayanese (talk) 12:15, 19 September 2008 (UTC)

Is it possible to edit the diagram to correct the misspelling of "fumarate"? Dasyornis (talk) 05:52, 30 October 2008 (UTC)

Good catch. Done. Narayanese (talk) 07:13, 30 October 2008 (UTC)

---

I have a new textbook from 2006 adapted from "Biological Science, second ediion" by Scott Freeman that uses "Krebs Cycle" consistantly, so some people do still use the name. Also, why is the word "skittles" in the article?

---

Two questions:

• What's the source for this image? I notice it's been uploaded to Wikipedia, but where's it from?
• Shouldn't it be located at Krebs Cycle (or, biologists, should that be Krebs cycle if it's often not used as a proper name)?

--Larry Sanger

---

1. it's Krebs cycle (lower case) according to two biochem texts I have handy
2. no-one calls it that anymore really; almost always its referred to as citric acid cycle.

- Iwnbap

---

I replaced it with my Nupedia article on the subject. I doubt much information was lost by that ;) Also, the images are mine, which solves the doubtful copyright problem. Looks like the tranition didn't go too well on the table, please help fixing it. --Magnus Manske

---

Gee whiz, its so worthwhile to spend time working on diagrams, when the entire article can just be replaced by Nupedia stuff. Wonderful.

Not to mention, of course, that I spent some actual time working on my diagram. Given the current upload protocol, it should be trivial to track the source of images, if you have copyright questions. Anyway, you've succeeded in souring me from drawing a diagram again. Good job! -Dlamming

---

I didn't know where the diagram was from; actually, I was suspicious of its origin because it looked too professional! Given the text accompanying it (which, as you will surely admit, was not the most complete description ever made;), I intended to be bold in updating pages (that was the recommendation of a higher authority; you know who) and just put the (existing) article in. If I hurt your feelings by removing your work, I'm sorry. If you need an excuse to reduce your input to wikipedia, go right ahead and blame me. Not that you could have said "I made this" on this page when the question came up, or re-replaced my image with yours (I still have it up at Nupedia, I wouldn't have a problem with that;). --Magnus Manske

My 2 and a half canadian cents

Well, it appears that my college-level Bio textbook refers to it as the Krebs cycle... while "Citric Acid cycle" doesn't even appear in the chapter (except as "it's also caled the citric acid cycle"), nor in the index (at all)... ugen64 22:39, Feb 4, 2004 (UTC)

I'll add some more points... the chief arguments against using Krebs cycle seem to be either: "Leave well enough alone", "used more in modern textbooks", and clarity/depersonalization. Well, Krebs received a Nobel Prize in Medicine.... so I suppose we should also rename all the radioactive elements named after people (who knows, Curie could have been a plagiarist, therefore, Curium isn't a good element name). Leave well enough alone doesn't deal specifically with the problem... and anyway, if that were the case, Krebs was the common name at first, therefore, it would be leaving well enough alone. I can't argue with "used more in modern textbooks", but there are some rather reputable biology textbooks that refer to it solely as the Krebs cycle (including Campbell, which I referred to above)... I really do not care if we change this article's name, I'm just throwing some points out. ugen64 23:32, Feb 4, 2004 (UTC)

Anyone considered whether your textbooks are US or from 'The rest of the World'? Personally, I never heard of Krebs until I saw this discussion, so I would like to ask whether Krebs is used mostly in US? (Might also be the case that I always paid more attention to chemistry classes than to biology...:) Maybe omeone could take a look at all these books referred to and see whether there are any correlation between (US/UK, Biology/Chemistry, Year of print...) and usage of Krebbs/CACMikez

Horrible problems

What happened to this page? Bensaccount seems to have dissected it... ugen64 21:07, Apr 3, 2004 (UTC)

Please Help! Would you Answer my question

-If Diabetes Mellitus Directly affect TCA Cycle Reactions or Not?

Introduction.

I'm not going to edit this, but I was reading the introduction, and it erroneously states that the Krebs Cycle uses Oxygen. Oxygen isn't used in metabolism until the oxidative phosphorylation stage in the mitochondria. Would someone please change this? Thanks. —Preceding unsigned comment added by 99.148.39.5 (talk) 00:36, 30 September 2009 (UTC)

The sentence in question stated, "The citric acid cycle [...] is a series of enzyme-catalysed chemical reactions of central importance in all living cells that use oxygen as part of cellular respiration." So what it says is that living cells that use oxygen have the TCA cycle. I've rephrased the sentence to "The citric acid cycle [...] is a series of enzyme-catalysed chemical reactions, which is of central importance in all living cell (biology)|cells that use oxygen as part of cellular respiration. I hope this change makes it now clearer. Malljaja (talk) 02:19, 30 September 2009 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Citric acid cycle/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Comment: This is high school/SAT biology content, part of cell metabolism. - tameeria 14:54, 18 February 2007 (UTC)

Last edited at 14:54, 18 February 2007 (UTC). Substituted at 08:53, 19 April 2016 (UTC)

Citric Acid Cycle Diagram

This diagram is really messy. The molecules could be less bulky looking. (having the molecules not be the stick and ball structure and instead have it be the normal structural formula) Also having backwards arrows on some reactions would help identify which steps are reversible or not.

Geowong (talk) 18:25, 18 March 2017 (UTC)

I agree with Geowong's comments. The diagram is hard to read because of the unfamiliar ball-and-stick representations. Also please remove the reaction of pyruvate carboxylase: having it in the diagram obscures the cyclic nature of the citric acid cycle. JoNo672 (talk) 14:49, 12 April 2018 (UTC)

Succinate dehydrogenase is a member of the electron transport chain as well as the TCA cycle; its substrate is succinate not FADH2

In summarizing the reducing equivalents provided to the electron transport chain, there is a complication in that succinate dehydrogenase (or rather Complex II) is part of both the TCA cycle and the electron transport chain. It is a little misleading to say 3 NADH and one FADH2 are provided: Yes, FAD is the cofactor in SDH that gets reduced first, but by the same token the NADH dehydrogenase has a flavin (mononucleotide) which accepts the electrons from NADH. The main substrates of the electron transport chain are NADH and succinate, not NADH and FADH2. However it can't be said that the cycle produces succinate, the way it produces NADH. It might be said that one turnover of the cycle supplies the ETC with 3 NADH and one succinate, then go on to explain that oxidation of succinate by SDH constitutes the first step in oxidation of succinate by the ETC, as well as a step in the TCA cycle. Or that might be even more confusing.
An easy way out would be to divorce Complex II from the respiratory chain and consider it only a member of the TCA cycle (albeit membrane bound), especially since there is no energy coupling in this step. Then we could say the TCA cycle provides 3 NADH and one ubiquinol to the electron transfer chain. But the long history of "Complex II of the respiratory chain" would make this problematic. Eaberry (talk) 05:26, 26 April 2018 (UTC)

Production of ATP

The citric acid cycle does not directly produce ATP, right? It produces reducing agents NADH and FADH that enter into the electron transport chain. — Preceding unsigned comment added by Greenriverglass (talk • contribs) 16:34, 13 July 2020 (UTC)

Wiki Education Foundation-supported course assignment

This article is or was the subject of a Wiki Education Foundation-supported course assignment. Further details are available on the course page. Student editor(s): Sneha.patel119.

Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 17:44, 16 January 2022 (UTC)

Good work, but

Hello Wikipedia (English),

my google search found: "New studies suggest that lactate can be used as a source of carbon for the TCA cycle." respect regarding the fast update.

I have to say, I am author of "Re-thinking the Citric Acid Cycle" https://www.mdpi.com/1422-0067/22/2/604

In this article we show a blueprint of the original CAC, copyrigth Nobel Foundation, H.A. Krebs, 1953. Substrate of the original CAC is lactic acid. Thus, "new studies" showing that circulating lactate is main substrate of the CAC, simply repeat the original concept of H.A. Krebs, or?

A century ago, 1922, O.F. Meyerhof was hounoured with the Nobel Prize for his "discovery of the fixed relationship between lactic acid and oxygen consumption". Even a century ago, it was lactic acid, not lactate. It is the kinetics of proton-linked monocarboxylate transporters which opens an understanding to transport of monocarboxylic acids.

By the way, Wikipedia (English) use the Title Tri-Carboxylic-Acid (TCA) but shows cycling carboxylates, and not acids. Stoichiometry of citrate-cycle-reaction is incorrect because of the changes in electric charges.

Wikipedia (Germany) is (of cause) more "correct" then WiKi (English). In WiKi Germany H.A. Krebs discovered the Citrate Cycle. Asking WiKi Germany why: regarding Nobel Prizes, Wiki German reflects common understanding and not the stuff found on the page of the Nobel Foundation.

I understand, that Wikipedia has to propagate textbook knowledge (common understanding). But recognizing the fast update - lactate is substrate-. Wiki (English) is faraway from common understanding.

To understand import of lactic acid against the environment/cytosol concentration gradient is non-equilibration thermodynamic. Energy has to drive the transport and is not driven by a concentration gradient (equilibration thermodynamics).

Not sure if I can handle setting my comment correctly.

Thanks for the fast update. 2001:16B8:1803:ED00:C1E2:4CB2:E3DF:47ED (talk) 08:13, 28 May 2022 (UTC)

Me again,

wikipedia talk picture of the day opens me a window for a talk of the picture of the day and not of June 17. For sure my misunderstanding.

nice future picture of the day. I like that reverse reaction are omitted. Burning is burning. I like mor that in the picute, not tex NADH and H+ is shown. Free H+ does not exist. Better will be NADH-H+.

Guess, everyone have had the time to recognized the error in the PDH, IDH and CS catalysed reaction? PDH: good to show NADH-H+, but were is the H+ coming from when pyruvate and not pyruvic acid is set as substrate? PDH belongs to enzyme family of 2-oxo ACID dehydrogenase.

IDH, good to show NADH-H+, but where is the H+ comming from when isocitrate and not isocitric acid is set as substrate. CS: two times negatively charged oxaloacetate condensed with charge neutral water and acetyl-SCoA to three-times negatively charged citrate?

Is the picture art, didactic or science? In the muggle world the principle of mass conservation has replaced the idea of the philosopher stone: changing water in wine, lead into gold or let atoms appear or disapper during formulation of a chemical formula belongs to magic.

Perhaps, it should be mentioned that the picture is didactically-based and for clarity stochiometry was omitted?

Going back to -lactate- source of tricarboxylic acid cycle. The Cori cycle was mentioned in this context.

F. Cori: “Some 50 years ago - in 1929, to be exact - we proposed a cycle of the glucose molecule which could be in turn liver glycogen, blood glucose, muscle glycogen. The conversion of lactic acid to liver glycogen would complete the cycle”.

Is the -lactate- mentioned by wikipedia the -lactic acid- F. Cori mentioned? Thypo or stochiometry and nomenclature are omitted for clarity?

2001:16B8:18EB:FD00:E57B:8E81:EDAA:8CFE (talk) 06:14, 29 May 2022 (UTC)

Featured picture scheduled for POTD

Hello! This is to let editors know that File:Citric_acid_cycle_with_aconitate_2.svg, a featured picture used in this article, has been selected as the English Wikipedia's picture of the day (POTD) for August 25, 2022. A preview of the POTD is displayed below and can be edited at Template:POTD/2022-08-25. For the greater benefit of readers, any potential improvements or maintenance that could benefit the quality of this article should be done before its scheduled appearance on the Main Page. If you have any concerns, please place a message at Wikipedia talk:Picture of the day. Thank you! Adam Cuerden ^(talk)_{Has about 7.8% of all FPs} 13:44, 23 May 2022 (UTC)

The citric acid cycle, also known as the TCA cycle (tricarboxylic acid cycle) or the Krebs cycle, is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. In addition, the cycle provides precursors of certain amino acids, as well as NADH, a reducing agent, which are used in numerous other reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest components of metabolism and may have originated abiogenically. The German-born British biochemist Hans Krebs received the 1953 Nobel Prize in Physiology or Medicine for his identification of the cycle in 1937. The name of this metabolic pathway is derived from citric acid, which is consumed and then regenerated by this sequence of reactions to complete the cycle. The cycle consumes acetate (in the form of acetyl-CoA) and water, and reduces NAD⁺ to NADH, releasing carbon dioxide. The NADH generated by the cycle is fed into the oxidative phosphorylation (electron transport) pathway. The net result of these two closely linked pathways is the oxidation of nutrients to produce usable chemical energy in the form of adenosine triphosphate. These processes are depicted in this overview diagram of the citric acid cycle.

Diagram credit: YassineMrabet; edited by Narayanese and TotoBaggins; vectorized by WikiUserPedia

Recently featured:

• Kobe Bryant
• The Goldfinch
• Wells Cathedral