Question

Put the following stages of cellular respiration in order from start to finish? Select one: O a glycolysis, pyruvate oxidation, Krebs cycle, electron transport chain Ob glycolysis, Krebs cycle, pyruvate oxidation, electron transport chain Oc glycolysis, electron transport chain, Krebs cycle, pyruvate oxidation od pyruvate oxidation Krebs cycle, glycolysis, electron transport chain

Answer 1

Option 1 is the correct answer, i.e. glycolysis, pyruvate oxidation, krebs cycle, electron transport chain.

There are 4 stages of cellular respiration:

1. Glycolysis. In glycolysis, glucose—a six-carbon sugar—undergoes a series of chemical transformations. In the end, it gets converted into two molecules of pyruvate, a three-carbon organic molecule. In these reactions, ATP is made, and NAD^{+ is} converted to NADH.

2. Pyruvate oxidation. Each pyruvate from glycolysis goes into the mitochondrial matrix—the innermost compartment of mitochondria. There, it’s converted into a two-carbon molecule bound to Coenzyme A, known as acetyl CoA. Carbon dioxide is released and NADH is generated.

3. Citric acid cycle. The acetyl CoA made in the last step combines with a four-carbon molecule and goes through a cycle of reactions, ultimately regenerating the four-carbon starting molecule. ATP, NADH, FADH² are produced, and carbon dioxide is released.

4. Electron Transport chain. The NADH and FADH² made in other steps deposit their electrons in the electron transport chain, turning back into their "empty" forms (NAD⁺ and FAD). As electrons move down the chain, energy is released and used to pump protons out of the matrix, forming a gradient. Protons flow back into the matrix through an enzyme called ATP synthase, making ATP. At the end of the electron transport chain, oxygen accepts electrons and takes up protons to form water.

respiration—pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation—require oxygen in order to occur. Only oxidative phosphorylation uses oxygen directly, but the other two stages can't run without oxidative phosphorylation.