Does glycolysis produce water or not?

[MedPR]

I've read different things about glycolysis and I'd like to know what the facts are.

My main question is What do we need to know about glycolysis, kreb's cycle, and the electron transport chain? I'm finding the topic of cellular respiration very foggy and difficult to grasp since so much of it (all of it) is/are a mechanism that I know we don't have to memorize.

My secondary question is does glycolysis produce water, or not? I thought it didn't, but then I came across this:

http://www.uccs.edu/~rmelamed/MicroFall2002/Chapter 5/glycolysis.jpg

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[silverice]

i would like to know as well

 

[jsp132]

seems to produce 2 H20

 

[rjosh33]

Glycolysis does produce water during the conversion of 2-phosphoglycerate to phosphoenolpyruvate (governed by an Enolase enzyme), as your link shows. However, you don't need to concern yourself with a detail like this for the MCAT.

Something as complicated as cellular respiration would almost certainly be explained in a passage. Details such as enzymes used to govern reactions and how many ATP produced per reduced coenzyme would likely be given. However, it'd be good to be familiar with concepts such as the difference between substrate level and oxidative phosphorylation, the chemiosmotic principle of the ETC, and how inhibitors would affect the process (how would the reactants back up, and where?).

Though, if you want to really get a good grasp on it, the following would be good to be familiar with...

Know the four steps of cellular respiration: glycolysis, decarboxylation of pyruvate to acetyl CoA, Krebs, ETC.

Know the main products of the first three steps (per glucose molecule):

Glycolysis: 2 net ATP, 2 NADH, 2 pyruvate
Decarb. of pyruvate: 2 NADH, 2 CO2, 2 acetyl CoA
Krebs: 6 NADH, 2 ATP (or GTP, same thing basically), 2 FADH2, 4 CO2

Know that the ETC uses NADH and FADH2 to create a proton gradient whose energy is then harnessed to produce ATP via ATP synthase (probably good to know how this happens, too).

Know where each occurs:

Glycolysis: cytoplasm
Decarb. of pyruvate: mitochondrial matrix
Krebs: mitochondrial matrix
ETC: inner mitochondrial membrane

Know the final electron acceptor (oxygen), and that it produces water when it gets reduced. Again, anything more specific will most likely be explained in a passage.

 

[SaintJude]

2 Additional Things:

Know that the carbon and oxygen of the glucose, will end up as carbon dioxide we exhale. And that the oxygen we inhale, will be converted into water at the end of ETC. Some may say that's not necessary to know, but it's also on Kaplan and mcat-review.org

Also, NADH is a higher energy carrier (produce more ATP ) than FADH2.

 

[MedPR]

Glycolysis does produce water during the conversion of 2-phosphoglycerate to phosphoenolpyruvate (governed by an Enolase enzyme), as your link shows. However, you don't need to concern yourself with a detail like this for the MCAT.

Something as complicated as cellular respiration would almost certainly be explained in a passage. Details such as enzymes used to govern reactions and how many ATP produced per reduced coenzyme would likely be given. However, it'd be good to be familiar with concepts such as the difference between substrate level and oxidative phosphorylation, the chemiosmotic principle of the ETC, and how inhibitors would affect the process (how would the reactants back up, and where?).

Though, if you want to really get a good grasp on it, the following would be good to be familiar with...

Know the four steps of cellular respiration: glycolysis, decarboxylation of pyruvate to acetyl CoA, Krebs, ETC.

Know the main products of the first three steps (per glucose molecule):

Glycolysis: 2 net ATP, 2 NADH, 2 pyruvate
Decarb. of pyruvate: 2 NADH, 2 CO2, 2 acetyl CoA
Krebs: 6 NADH, 2 ATP (or GTP, same thing basically), 2 FADH2, 4 CO2

Know that the ETC uses NADH and FADH2 to create a proton gradient whose energy is then harnessed to produce ATP via ATP synthase (probably good to know how this happens, too).

Know where each occurs:

Glycolysis: cytoplasm
Decarb. of pyruvate: mitochondrial matrix
Krebs: mitochondrial matrix
ETC: inner mitochondrial membrane

Know the final electron acceptor (oxygen), and that it produces water when it gets reduced. Again, anything more specific will most likely be explained in a passage.

2 Additional Things:

Know that the carbon and oxygen of the glucose, will end up as carbon dioxide we exhale. And that the oxygen we inhale, will be converted into water at the end of ETC. Some may say that's not necessary to know, but it's also on Kaplan and mcat-review.org

Also, NADH is a higher energy carrier (produce more ATP ) than FADH2.

Thanks guys.

Is it correct to say that glycolysis is the reduction of glucose?

 

[rjosh33]

Thanks guys.

Is it correct to say that glycolysis is the reduction of glucose?

Just the opposite -- it's the oxidation of glucose. Note the chemical equation for cellular respiraton:

Glucose + 6 02 --> 6 CO2 + 6 H2O (+ Energy)

While glycolysis doesn't completely comprise this formula, glucose is getting oxidized to pyruvate while NAD+ is reduced to NADH.

 

[SaintJude]

No. Glycolysis is the oxidation of glucose. I kept on getting this confused, until someone gave me a hint that ended the confusion:

In the big picture of cellular respiration, oxygen is final electron acceptor and O2 is reduced to H20. And glucose is oxidized, as part of this redox process.

 

[MT Headed]

2 Additional Things:

Know that the carbon and oxygen of the glucose, will end up as carbon dioxide we exhale. And that the oxygen we inhale, will be converted into water at the end of ETC. Some may say that's not necessary to know, but it's also on Kaplan and mcat-review.org

Also, NADH is a higher energy carrier (produce more ATP ) than FADH2.

I disagree with the bolded part. There is a lot of monkey chemistry going on with the oxygens, for instance inorganic phosphate appearing (PO4) and later getting attached to ADP as a PO3 extension. The net result of a reaction like this is to deposit an oxygen on the molecule (therefore oxidizing it).

Stick with the carbons of glucose ending up in carbon dioxide, and the oxygens of glucose just kinda get used up.

 

[MedPR]

I disagree with the bolded part. There is a lot of monkey chemistry going on with the oxygens, for instance inorganic phosphate appearing (PO4) and later getting attached to ADP as a PO3 extension. The net result of a reaction like this is to deposit an oxygen on the molecule (therefore oxidizing it).

Stick with the carbons of glucose ending up in carbon dioxide, and the oxygens of glucose just kinda get used up.

Typically I would go with mcat-review, but MT has proven him/herself time and time again. If anyone is interested, here is what mcat-review says about it.

6CO2: this is carbon dioxide produced by the Krebs cycle. Both the carbon and oxygen in this CO2 comes from the metabolite (glucose).
6H2O: this is water produced in the electron transport chain. The oxygen comes completely from the molecular oxygen that you breath in.
If we were to follow the carbon in the metabolite (glucose), it will end up in carbon dioxide.
If we were to follow the oxygen in the metabolite (glucose), it will end up in carbon dioxide.
If we were to follow the oxygen you breath in, it will end up in water.

 

[MT Headed]

I think we had this discussion last week. The water that is kicked off in step 9 of glycolysis has an oxygen from glucose, and one of the three oxygens in pyruvate actually came from inorganic phosphate. But again, this is the kind of trivia that would not be tested on the MCAT. It would be tested in your biochem class when you learn to follow the oxidation number of each carbon for energy purposes.