Talk:Cellular respiration

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high school/SAT biology content; changed importance to "high" for consistency with other cell metabolism subtopics - tameeria 14:59, 18 February 2007 (UTC)

Contents

[edit] Original author's note

This pages content comes from what I've learned in high school biology. Some of it may be incorrect. Also, I'm guessing that there's just a little more that could be added. By all means, do so (of course, that's what the 'pedia is all about). --bdesham


The biochemistry I was taught that cellular respiration is a process that describes the metabolic reactions and processes that take place in a cell to obtain energy via transferring electrons to an inorganic electron acceptor, usually oxygen. The reactions described in the "anaerobic respiration" section are not respiratory at all, rather they are fermentation reactions. Unless things have changed in the last 10 years, glycolysis (EMP pathway) serves as the front end for both respiration (TCA cycle and electron transport system) and fermentation (transferring electrons to organic molecules resulting in things like ethanol and lactic acid). Can others comment on the basic definition of respiration? Nbjansen 04:18, 11 March 2007 (UTC)

[edit] Table / flow chart

I've added a basic diagram covering the subprocesses of aerobic respiration.I've done it as a table rather than uploading the whole thing as a .png so that others can easily modify the info. However looking at the edit page the table looks complicated and offputting. If anyone wants to amend the content of the diagram but is put off editing the table by all the ugly HTML by all means let me know on my talk page and I will edit the table for you. Theresa knott 13:56 6 Jun 2003 (UTC)

Yeah, that table is kinda offputting. I've made a flow chart in PNG format; if anyone needs/wants to change it, visit User Talk:Bdesham and say so. --bdesham 19:43 9 Jun 2003

i agree........

[edit] Incorrect number of ATP?

I wasn't going to say anything, since my knowledge is limited to high school bio, but when I see this page was also made with that knowledge...we were taught a net gain of 36 ATP, not 38...perhaps you forgot to subtract the 2 used in glycolysis? EDIT: In fact, the glycolysis article agrees with me--kreb's and the ETC makes 34 ATP/glucose. 24.218.58.113 19:39, 26 Nov 2004 (UTC). Further edit: the previous was me, I am a new user. After referencing my biology textbook, the real answer (I believe) is that 38 ATP is the *optimal* gain, generally not realized due to such losses as the energy needed to move pyruvate into the mitochondria. I will make a minor edit to reflect this; please correct me if this is the wrong action. Endersdouble 19:47, 26 Nov 2004 (UTC)

Hmm... looking back at my notes from HS Biology, they say that the total gain of ATP from glycolysis and aerobic respiration is 38 (2 from glycolysis and 36 from aerobic respiration). I googled for "cellular respiration", though, and I found [1]. If you look under the "How many ATPs?" section, it says that the theoretical total is 38, but that due to conditions the number rarely exceeds 30. I'll look into this more when I have time. Cheers! --bdesham 19:49, 26 Nov 2004 (UTC)

This is how it works: In vitro (in a test tube with every ezymers, substrates at the right conditions), a biochemist can make 38 molecues of ATP from a molecule of glucose. However, in a eucaryotic cell, Glycolysis (which produces ATP and NADH)occurs in the cytoplasm while respiration (and the recycling of NADH) occurs inside the mitochomdria. And this is the problem: -- All the NAD in the cytoplasm would become NADH and glycolysis will stop due the the lack of NAD; Therefore, NADH in the cytoplasm must be transported into the mitochondria to unload its protons and electons (i.e NADH--> NAD). This transporting cost 2 ATP; thereforem in eucaryotes, we said they produce 36 ATP. However, these type of calculation is meaningless-- If all glucose are committed to produce ATP and CO2, all living organisms will be the same- pails of ATP! The fact is, a cell will not produce a single molecue of ATP more than it need.

Ok so looking at this it all fine and dandy but im taking bio right now and im preety sure it is 36 ATP but then aging maby im wrong this seems to be quite a perdiciment. —The preceding unsigned comment was added by 67.58.207.41 (talk • contribs).
38 and 36 are purely theoretical numbers; read the section Theoretical_yields. But if we have to go with 36 or 38 then 36 is a more accurate estimate (but still pretty bad) of the most ATP that can be produced from a molecule of glucose. David D. (Talk) 15:36, 3 October 2006 (UTC)
Even if 36 is more accurate than 38, the fact remains that the numbers are purely theoretical, so how close they are to the actual number of ATP produced should not be relevant. From what I have studied in Biology, 38 is the maximum number of ATP molecules that could potentially be produced, hence the theoretical number of ATP molecules produced by one molecule of glucose should be 38. EatMana 17:14, 24 January 2007 (UTC)
This is not correct. 38 is impossible since the two NADH are outside the mitochondria. When the text books use 38 they assume those NADH can be used inside the mitochondria. That is wrong. If that is what your text book says then write to the author and get him/her to correct the error. David D. (Talk) 05:46, 25 January 2007 (UTC)

[edit] Should this be merged with "Glycolysis?"

Reading this article and Glycolysis, I've noticed that they duplicate a lot of information. Should they be merged?

I think it would be better to de-emphasise glycolysis on this page. This page should be an overview whereas the glycolysis page should be more detailed. David D. (Talk) 20:06, 28 October 2005 (UTC)
I agree, it's good to have separate ones. This summarizes and shows its place, glycolysis can be for more extensive detail and general interest not related to other cellular respiration processes. Tyciol 20:26, 5 October 2006 (UTC)

[edit] Link reaction

Shouldn't the link reaction be included here? although an apparently small step in the respiration and metabolic process it is none the less vital as without Acetyl CoA the Krebs Cycle could not occur. -Unknown

[edit] Efficiency of cellular respiration

The actual yield is closer to 30 ATP molecules. User:69.113.3.155

By the way i do agree that there needs to be more work the inefficency but what is the basis for that number of 30ATP's per glucose being 'normal'? The inefficiency of the proton pumping, leakyness of the inner membrane to protons or that intermediates from glucose to CO2 are continually being syphoned off for other metabolic reactions? I'm not sure we want to put a number on this since it seems that the efficiency would vary depending on the other metabolic reactions occuring in a cell at any given time.
Same with the efficiency of the ETC which may vary depending on the flux through the pathway. For example, I would imagine the efficiency would decrease during hypoxia or when ATP levels are high since the maximum PMF would be produced under those conditions. However, it may be highly efficient when a lot of oxygen and ADP are available.
Do you have any more information? David D. (Talk) 22:50, 21 November 2005 (UTC)
I agree; the energy charge (roughly the ratio of ATP to ADP and AMP) and availability of molecules or requirements of the cell in terms of biosynthesis, would affect how much of the glucose and its metabolites are actually shuttled into oxidative phosphorylation and ATP synthesis. Also, uncoupling proteins, e.g. UCP-1, have been found in the inner mitrochondrial membrane, and are believed to act as (tightly regulated) proton channels that allow protons to reenter the matrix, but without formation of ATP, like a sort of energy shunt. I think they are thought to play important roles in heat generation, metabolic energy processing, and are perhaps also involved in the development or control of conditions such as obesity (this article, for example, describes some of the UCP family of proteins and what their functions could be in living organisms). I also imagine that blocking the electron transport chain, removing electrons from the electron carriers, or lessening the proteins' abilities to pump protons may also reduce ATP synthesis further. Agaricus 17:34, 26 November 2006 (UTC)

[edit] Added a "See also" section

In the Electron transport chain discussion pages, we noted that there are lots of pages on this subject without adequate cross-referencing. I added a See Also section to help correct this problem. -Rozzychan 18:04, 23 June 2006 (UTC)

[edit] Revertion

"Cellular respiration, involves the exchange of gasses (oxygen and carbon dioxide) between capillary beds in the systemic loop of circulatory system and the interstitial fluid of the tissues of the body."

I just deleted the sentence above since this article does not deal with this definition at all. Is there a cite for cellular respiration being a description of the extracellular gas exchange? Maybe this information is better suited to the disambiguation page? David D. (Talk) 22:52, 13 August 2006 (UTC)

[edit] Fat oxidation?

I'm hoping someone can help me understand where fatty oxidation occurs in this aerobic metabolism, as I can't find it mentioned in the article (are my observation skills bad?). Even if not mentioned, since fat metabolization does take part with oxygen, it might be relevant, and the role of glucos metabolism in running fatty acid oxidation processes. Tyciol 20:26, 5 October 2006 (UTC)

Fatty acid oxidation is indeed aerobic in humans and animals, and begins with the transport of fatty acid chains into the mitrochondria by the "carnitine shuttle". The fatty acid chains are linked to Coenzyme A (CoA) inside the mitrochondrion to form an acyl CoA molecule, and a series of reactions, termed "beta-oxidation", then occurs. The beta carbon, carbon 3 of the fatty acid chain, is oxidised and hydrated to a keto group, and another molecule of CoA then cleaves this molecule between carbons 2 and 3. This forms a molecule of Acetyl CoA, which can enter the Krebs Cycle, and an Acyl CoA which is now 2 carbons shorter. The process is repeated until the fatty acid chain is completely degraded into Acetyl CoA, or for odd-chain fatty acids, Propionyl CoA. Propionyl CoA is converted in a series of reactions to Succinyl CoA, which is also an intermediate in the Krebs Cycle.
Animals do not have the ability to convert Acetyl CoA to glucose (plants can do this by utilising the glyoxylate cycle, which animals do not possess the enzymes for), and so almost all the ATP energy obtained from fatty acid oxidation must come directly from the Krebs Cycle and oxidative phosphorylation, both of which require oxygen to function. This inability to synthesise glucose from Acetyl CoA means that glucose metabolism is essential for the oxidation of fatty acids. Oxaloacetate, the compound that Acetyl CoA condenses with to form Citrate in the first step of the cycle, must be present for the cycle to run. It can be generated from pyruvate by pyruvate carboxylase (generated from glucose, other carbohydrates, glycerol and some amino acids in glycolysis) as well as replenished by the addition of intermediates into the Krebs Cycle itself (such as from some other amino acids and odd-chain fatty acids). Without enough oxaloacetate, Acetyl CoA cannot then be metabolised by the Krebs Cycle, and instead is funneled into ketogenic pathways to form "ketone bodies", such as acetoacetate. During times of starvation, when glycogen and carbohydrate reserves are depleted, muscle tissue breakdown is very important because many amino acids can be converted to pyruvate or Krebs Cycle intermediates, and these can then be used to generate oxaloacetate to keep the Krebs Cycle running, as well as allowing gluconeogenesis to occur. (Most of this information I extracted from Biochemistry, 6th ed., Borg et al., Chapters 17, 22 and 27)) Agaricus 18:47, 26 November 2006 (UTC)


There are a few articles like this one, like Complete Glucose Breakdown, Respiration (physiology) and Carbohydrate catabolism that appear to cover similar areas vaguely, but in a rather disjointed and confusing fashion. I personally think these should be merged or their contents combined into one single respiration overview article (i.e. giving details on how all the different pathways are combined in a typical cell to generate energy). Links to all the major reaction pathways involved in respiration could then be placed on this single page, which I think would help to make it a little easier to get a general overview of the whole topic. Alternatively, these could be merged into the Cell metabolism topic, with that page being the overview, but I personally think that catabolism and anabolism are two different things, and should have at least one page covering each separately. Any opinions? Agaricus 18:47, 26 November 2006 (UTC)

I think all the points you make ar sensible. i would encourage you to just go ahead and start editing if you have a plan. Others will probably kick in and help once you get the ball rolling. David D. (Talk) 07:33, 27 November 2006 (UTC)

[edit] Article Updating/Metabolic Integration

I've just edited the introductory paragraph to cover respiration in a more general way (rather than simply focusing on glucose and aerobic respiration), although I'm not sure if the style of writing is unclear or not (please let me know if it is).

As for the plan, I imagine the overall goal for this article would be to describe and link to each of the major metabolic pathways involved in cell respiration, but to do this in a general, integrated fashion. So, for example, we could first describe the outline pathways of glycolysis, the Krebs Cycle and oxidative phosphorylation as the "major" respiration pathways. Then, we could consider the entry points of other carbohydrates (including glycogen), amino acids and fat breakdown products into this outline scheme. The ATP generation chart in this article is useful, but perhaps it is more suited, in its full form, to being on the Oxidative phosphorylation page instead (since it is mostly specific to that particular process, rather than to respiration in general). In the end (although I doubt I'll actually do enough editing to play a major part in it), I imagine that we'd want all of the metabolism articles organised in this way, with a general overview page that covers all the major pathways at once, with links to the topics covering each of the pathways in more detail (I think it's harder to appreciate the complexity and interlinking of metabolic pathways without considering metabolism as a whole).

I'll start to make edits when I have the time, but if anyone else wants to do any editing, or has any suggestions to make about the "plan" I propose above, please feel free to do so. (Edit: Forgot the signature) Agaricus 20:07, 27 November 2006 (UTC)

[edit] Aerobic respiration

In Aerobic respiration 38 ATP molecles are made and in anaerobic respiration 2 are made. Aerobic respiration is for multicellular organisms and anaerobic respiration is for bacteria. 2 ATP molecules would not sustain our energy needs.

There is no scenario where 38 ATP is possible. The two NADH from glycolysis can never be used to give 3ATP even if the whole system is running at maximum efficiency. Energy is needed to shuttle the NADH reducing energy to the ETC so electrons will not pass through complex one when glycolytic NADH is oxidised.
Yeast are not bacteria and use anaerobic respiration. There are plenty of aerobic microbes too. Why do you assume that 2ATP from glycolytic oxidation could not be enough energy to sustain multicellular life? David D. (Talk) 06:07, 1 December 2006 (UTC)

[edit] Article merge

Instead of puting links to the real articles such as anerobic respiration, maybe someone should place a copy in this article.--75.28.161.31 03:59, 1 December 2006 (UTC)

No, it would be too big. This article is an outline of the processes involved. David D. (Talk) 06:07, 1 December 2006 (UTC)

[edit] Merge with respiration (physiology) ?

Respiration (physiology) is a brief, over-arching wikipage that could accept cellular repiration quite nicely, since it overlaps it by talking about aerobic and anaerobic metabolism. Any ideas here? Rhetth 20:33, 21 December 2006 (UTC)

I don't recommend it. Cellular respiration is a very large and specific subject, as any biochemistry student who has ever endured it knows very well. Really, the minute details of oxidative phosphoylation do not need to live in what should be a broader-scoped physiology article. – ClockworkSoul 23:44, 21 December 2006 (UTC)

[edit] Incorrect Information

I would like to clarify that under anaerobic respiration, you talk about a fermentation process. Note: anaerobic respiration and fermentation are two completely different processes. Anaerobic respiration is very similar to aerobic fermentation, utilizing the pyruvate decarboxylase step, entering the TCA cycle, and undergoing electron chain transport. The difference is that the final electron acceptor is a molecule other than O2. It can be a variety of molecules such as NO3-, SO42-, etc. Fermentation, on the other hand, undergoes glycolysis and then pyruvate can enter a variety of pathways, such as homolactic/heterolactic fermentation, mixed acid fermentation, and ethanol fermentation. And as for the number of ATP produced, many text books have a range from 36-38 ATP net production. And I don't agree that cellular respiration should be merged with glycolysis. Glycolysis is one of four steps in cellular respiration (4 if you count the conversion of pyruvate via pyruvate decarboxylase). Many a link can be established to glycolysis but I don't recommend merging the information. Ambrish100 03:14, 14 March 2007 (UTC)

Regardign your three points:

  1. I agree with the anaerobic respiration versus fermentation distinction.
  2. As for the 36-38, the text books are wrong. And some text books, such as Workd of the Cell, Becker et al. get it right.
  3. I'm not sure I understand the last point. Isn't this article is an overview of the four steps of cellular respiration, why wouldn't glycolysis be mentioned here? There is a seperate article on glycolysis that expands on the details.

David D. (Talk) 06:02, 14 March 2007 (UTC)

Response: For my last point, I was just agreeing with you in one of your previous responses. Ambrish100 19:20, 16 March 2007 (UTC)

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