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Anaerobic bacteria utilise glycolysis:

Glucose + 2 P + 2 NAD+ => 2 ATP + 2 H + 2 NADH + 2 H2O + 2 Pyruvate

followed by fermentation:

Pyruvate + NADH => Lactate + NAD+

The resultant NAD+ formed can then be used again to break down more glucose molecules in glycolysis to produce ATP.

However, besides NAD+, glycolysis also requires an input of 2 ATP at the beginning (for the phosphorylation of glucose to glucose 6P, and fructose 6P to fructose 1,6 BP)

Since only 2 ATP is produced from glycolysis initially, would these 2 ATP be reused in another round of glycolysis?

If so, how do anaerobic bacteria produce a net amount of ATP for cell activities and growth?

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    $\begingroup$ Please go back and check your sums and re-read the chapter in your text book, taking particular account of the fact that two molecules of triose are produced from one hexose. $\endgroup$
    – David
    Commented Sep 9, 2018 at 9:23
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    $\begingroup$ That was already accounted for in the balanced equation above. 4 ATP - 2 ATP invested is a net of 2 ATP from glycolysis. $\endgroup$
    – user60513
    Commented Sep 9, 2018 at 10:32
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    $\begingroup$ What do you mean by "reused"? The net gain of the fermentative type of anaerobic energy extraction from glucose is 2ATP---which is available for cellular processes that need ATP to proceed. Note, that there are two ways to regenerate NAD+: fermentation (which you mention) and anaerobic respiration (which you do not mention); the net gain of anaerobic energy extraction from glucose involving anaerobic respiration is 2ATP & 2NADH, because the latter can be used to generate ATP (via ATP synthase). $\endgroup$
    – user37894
    Commented Sep 9, 2018 at 21:29
  • $\begingroup$ Your response to my comment is incorrect. As I said, please go back to your text book and look at the pathway of glycolysis and the actual reactions where ATP is generated and whether the substrate is triose or hexose and if it is triose how many trioses came from the original hexose. $\endgroup$
    – David
    Commented Sep 10, 2018 at 21:43
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    $\begingroup$ @user1136 — The equation given by OP is not quite right. It lacks ADP and appears to involve phosphorus and molecular hydrogen. If the OP recognized that there was a net yield of 2ATP he would have included 2ATP on the left-hand side of the equation and 4ATP on the right. Indeed, if he had recognized there was a net yield of ATP he would not have entitled his question as he has. He obviously thinks there is no net yield because he has forgotten to multiply by 2 after aldolase. Perhaps that's why he has kept a low profile in the month since he posted. He may even have taken my original advice. $\endgroup$
    – David
    Commented Oct 9, 2018 at 22:40

3 Answers 3

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The product is 4 ATP not 2, 2 is the net product because two are used to start the reaction.

Looking at the complete glycolysis reaction helps.

enter image description here

ATP can be used to start another round of glycolysis which yields 4 ATP which can then start 2 rounds of glycolysis which yields 8 ATP, rinse, repeat. It is an exponential process, ATP can be taken from this for other processes since as long as you still have 2ATP around to can restart the exponential cascade. For example from the yielded 8 if you take half for other uses, you still get 8 ATP from the next round of glycolysis reactions.

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During the reactions, the resultant molecules are dispersed in the cytosol, and it is a bulk phenomenon rather discrete and independent event. The calculations are mainly based on in vitro experiments, so the reuse of the energy transporter molecules (ATP), totally depend on it's quick availability.

The NET production of ATP cannot be determined in precised manner as pathways may show reuse of the formed energy bags (ATPs) or may use already present molecule or molecules from some other reaction.

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    $\begingroup$ @VishalKumarSahu Can you please provide some references to support your answer? $\endgroup$
    – WYSIWYG
    Commented May 8, 2019 at 13:36
  • $\begingroup$ There is a lot of theory and scientific articles available through google. If this is a scientific (not for general people) forum, please let me know, I would not use researchgate, pubmed... $\endgroup$
    – Vishal Kumar Sahu
    Commented Jan 22, 2020 at 10:17
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Anaerobic respiration, which is used by some Bacteria and some Archaea, is not glycolysis+fermentation. Anaerobic respiration is like aerobic respiration which includes ETC (electron transport chain). Basic difference is the terminal electron acceptor. In aerobic respiration the terminal electron acceptor is oxygen. On anaerobic respiration the terminal electron acceptors are various materials, for example hydrogen sulfide. Read this or research similar sources.

In Turkey, we were teaching anaerobic respiration and fermentation as the same things in high school biology lesson until a couple of years ago. May be you are asking in this regard. If so, rename your question.

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