[High School - Biology] Kreb's Cycle and Electron Transport

[og4lif]

I've been reviewing my notes for an upcoming biology exam and I've run into a problem. I know that Oxygen is required for the Kreb's Cycle to occur but I'm unsure of why oxygen is required? I do know that without Oxygen the Kreb's Cycle would not occur.


Here is what I think. Please let me know if this is correct.

NADH and FADH2 are products formed in the Kreb's cycle as well as glycolosis. I know that NADH and FADH2 are directly involved with electron transport, as they give up their electrons and H+ to the electron tranport chain composed mostly of cytrochromes. As the electrons reach the end of the electron transport chain they are used to produce water in order to discard the electrons. Therefore, I know that Oxygen is needed for electron transport but I'm still unsure of how Oxygen is needed for Kreb's cycle. I'm guessing that without Oxygen, the electrons will be immediately picked up by NAD+ and FAD which will reduce the amount of free NAD+ and FAD avaiable for the Kreb's cycle.

[madmatt621]

Originally Posted by og4lif

NADH and FADH2 are products formed in the Kreb's cycle as well as glycolosis. I know that NADH and FADH2 are directly involved with electron transport, as they give up their electrons and H+ to the electron tranport chain composed mostly of cytrochromes. As the electrons reach the end of the electron transport chain they are used to produce water in order to discard the electrons. Therefore, I know that Oxygen is needed for electron transport but I'm still unsure of how Oxygen is needed for Kreb's cycle. I'm guessing that without Oxygen, the electrons will be immediately picked up by NAD+ and FAD which will reduce the amount of free NAD+ and FAD avaiable for the Kreb's cycle.

Two carbons are oxidized to CO2, and the energy from these reactions is transferred to other metabolic processes by Guanosine triphophate (or Adenosine triphophate), and as electrons in NADH and FADH2. The NADH generated in the TCA cycle may later donate its electrons in oxidative phosphorylation to drive ATP synthesis; FADH2 is covalently attached to succinate dehydrogenase, an enzyme functioning both in the TCA cycle and the mitochondrial electron transfer chain in oxidative phosphorylation. FADH2 thereby facilitates transfer of electrons to coenzyme Q, an intermediate in the electron transfer chain.

In step nine of the citric acid cycle, the substrate Fumarate + H2O products L-Malate and the enzyme is Fumarase. The reaction type is H2O addition (hydration).

In step ten (final step), the substrate L-Malate + NAD+ products Oxaloacetate + NADH + H+ and the enzyme is Malate dehydrogenase. The reaction type is Oxidation (generates NADH (equivalent of 3 ATP)).

edit: The citric acid cycle is part of a metabolic pathway involved in the chemical conversion of carbohydrates, fats and proteins into carbon dioxide and water to generate a form of usable energy.

edit:edit: Someone correct me if I'm wrong.

[sumzup]

You are correct in that Oxygen functions as an electron acceptor (see oxidative phosphorylation); energy released through the redox reactions involved allows for the production of ATP.

If Oxygen wasn't there to accept the electrons, there would be less NAD+ and instead more NADH. Respiration would still be carried out, but instead through lactic acid fermentation; the rxn is: pyruvate + NADH -> lactic acid + NAD+. The NAD+ would then be used to produce ATP. Side note: Thus, after a heavy workout or something when there is a limited Oxygen supply to the muscles, cells turn to anaerobic respiration causing a build-up of lactic acid and as a result the soreness and usual symptoms.

[MeaCulpa]

Oxygen's not needed in the Kreb's Cycle directly, but it needs to be present in order to keep the cycle going. As you mentioned, if oxygen is absent, water cannot be formed at the end of the ETC. Hence, the electron transport chain shuts down without oxygen. This causes a buildup of precursors formed during the Krebs Cycle.

I don't know how much you may have learned about allosteric enzymes and equilibrium, but this buildup of intermediates inactivates certain enzymes involved in the Krebs Cycle, preventing it from going any further. With the Krebs Cycle shut down, all the pyruvate can do is ferment in order to get a few ATP and to regenerate NAD+.

[guyofgod]

ATP is like a fully charged battery and ADP is like a partially charged battery.

ATP has 3 phosphate groups where as ADP has only 2. If you add another phosphate group to ADP, then you have ATP which can only release energy by braking that ATP into ADP and the (I think it's Calvin Cycle) starts all over again. I just finished this section in my Biology Class

[GuidoHunter]

You really oughtn't misspell the Krebs cycle.

--Guido

http://andy.mikee385.com

[guyofgod]

Originally Posted by GuidoHunter

You really oughtn't misspell the Krebs cycle.

--Guido

http://andy.mikee385.com

If you say so cheif.....

[Blue June]

geesh that was on my last semester exam for Biology. it really doesn't get easier next semester. Dx