fermentation of lactic acid

[LaAmadeus]

Hai everyone, im new to this forum and i am really confuse and curious about this. In cellular respiration, there are three process, glycolysis, kerbs cycle and electron transport chain. Kerbs cycle and electron transport chain cant proceed without the presence of oxygen. So the only possibilities on how the energy is produced during anaerobic respiration is through glycolysis. The output of glycolysis is 2 pyruvic acid, 2NADH, 2H20 and 2ATP. The thing that doubt me is that pyruvic acid must undergo fermentation to form lactic acid. But the thing is one of the output of glycolysis is NADH not NADH2. Whereas the equation shows that 2C3H4O3 + NADH2 --> 2C3H6O3 + NAD + 2ATP.

 

Im sorry, this may sounds a bit complicated but i really need guidance.

I know that this is a very broad and complicated topic.

Please correct me if im wrong.

 

Thanks

[CharonY]

Kerbs cycle and electron transport chain cant proceed without the presence of oxygen.

This is incorrect, the Krebs cycle does not require oxygen.

Also, not all electron transport chains end with oxygen, though the textbook versions generally mean the type of oxidative phosphorylation that uses oxygen as terminal electron acceptor.

From your question I assume you are confusing things here, as lactic acid fermentation is a process different from glycolysis (and there are again several versions of it out there). So basically, why do you think that pyruvate has to be fermented to lactate? What kind of respiration are we talking here about and which organism?

[MBGuru]

...But the thing is one of the output of glycolysis is NADH not NADH2. Whereas the equation shows that 2C3H4O3 + NADH2 --> 2C3H6O3 + NAD + 2ATP.

 

Im sorry, this may sounds a bit complicated but i really need guidance.

I know that this is a very broad and complicated topic.

Please correct me if im wrong.

 

Thanks

 

Strictly speaking the output of Glycolysis is NADH + H+. Why is that? The oxidized form of the NAD cofactor, NAD+, can only accept a hydrogen (H) and an electron in order to be converted in its reduced form NADH. Since a compound loses 2 hydrogen atoms (each atom consisting of a proton and an electron) where does that extra proton (H+) go if it is not accepted by NAD+? It joins the environment, the solution in which the reaction occurs.

 

So a reaction in which a compound is oxidized by an enzyme that uses NAD as cofactor should be written as

 

Compound-H2 + NAD+ -> Compound + NADH + H+

 

and the reduction reaction should be

 

Compound + NADH + H+ -> Compound-H2 + NAD+

 

NAD+ is often presented as NAD, while NADH + H+ (or most commonly NADH) as NADH2.

 

For mass relations purposes in that equation the authors had to use NADH2 to show where the second hydrogen for the lactic acid comes from. Yet that equation is still not good, it has to be written as

 

2C3H4O3 + 2NADH2 --> 2C3H6O3 + 2NAD