CELL RESPIRATION
THE KREBS CYCLE
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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without oxygen, NADH cannot be oxidized to continue receiving electrons as NAD+
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without oxygen, coenzyme A is unable to be added to the pyruvate molecule to make acetyl CoA
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without oxygen, ATP cannot be synthesized by substrate level phosphorylation
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without oxygen, glycolysis cannot take place to provide the starting materials for the Krebs cycle
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Detailed explanation-1: -The Krebs cycle, by itself, does not require the presence of oxygen; this element is necessary for the last stage of aerobic cellular respiration, i.e., oxidative phosphorylation. Organic molecules endowed with energy (carbohydrates, lipids, proteins) are split in previous reactions.
Detailed explanation-2: -Introduction. In the presence of oxygen organisms are capable of using the Kreb’s Cycle. The reason oxygen is required is because the NADH and [FADH2] produced in the Kreb’s Cycle are able to be oxydized in the electron transport chain (ETC) thus replenishing the supply of NAD+ and [FAD].
Detailed explanation-3: -Step 8: In the last step of the Krebs cycle, malate is converted to oxaloacetate. In the process, NAD+ is reduced to form NADH + H+. Oxaloacetate can then accept another acetyl CoA and begin the Krebs cycle again.
Detailed explanation-4: -It plays a key role in energy metabolism by accepting and donating electrons. The low energy form NAD+ shown at left is raised to the high energy form NADH. The change in the form of the active nicotinamide group in NADH is indicated above. It accepts two electrons and a hydrogen in reaching the high energy state.