Explain the Krebs cycle.

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caledon | High School Teacher | (Level 3) Senior Educator

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The Krebs cycle is simply another name for the Citric Acid Cycle, so named for the researcher who identified the complete cycle in 1937.

This cycle describes a series of chemical reactions that take place in all aerobic organisms (aerobic meaning that they use oxygen to facilitate their metabolism, like we do). The cycle is pretty complicated, there are many steps, many reactants and many product, and the cycle can be modified or affected by a variety of factors. However the essential function is to create ATP, the "energy molecule" from the carbon sources that the organism ingests. 

Glucose is typically given as the starting molecule, which we ingest by eating, and plants ingest via photosynthesis. The glucose is broken down by glycolysis and decarboxylation to become acetyl-CoA; these steps are not part of the Krebs process. The Krebs process then performs a number of reactions which produce ATP, NADH, ubiquinol and carbon dioxide, although not all at once. The carbon dioxide is excreted, the ATP is used throughout the body for energy, and the NADH and ubiquinol are reused or reacted in other metabolic processes to produce different compounds.

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anjna | College Teacher | (Level 1) eNoter

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The citric acid cycle is a series of reaction in mitochondria that oxidize acetyl CoA to form ATP in aerobic environment.

The cycle start with production of citrate in reaction of acetyl CoA & oxaloacetate.  The acetyl CoA comes from metabolism of carbohydrate, protein & fat. This citrate is degraded by a series of dehydrogenation and decarboxylation and finally oxaloacetate is regenerated. The important product of cycles are citrate, alpha-ketoglutarate, succinate, fumarate, malate and 3 NADH,1 FADH2, 2 CO2 & 1 ATP(per cycle). This NADH & FADH2 act as a substrate in oxidative phosphorylation to form 2.5 & 1.5 ATP respectively.

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rachellopez | Student, Grade 12 | (Level 1) Valedictorian

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The Krebs cycle takes place in the mitochondrion and has 8 steps, or reactions. During these reactions, two carbon molecules are changed into CO2 (carbon dioxide). The chemical equation that represents the reactions is:

acetyl CoA + 3 NAD + FAD + ADP + HPO4-2 ---------------> 2 CO2 + CoA + 3 NADH+ + FADH+ + ATP

The main purpose of these reactions is the convert/breakdown glucose and make ATP (energy molecules). The Krebs Cycle is only one part of the whole breaking down process. The main thing that occurs in the Krebs Cycle is the production of ATP and NADH as well as ubiquinol and CO2, which are used for energy and making new compounds.

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udonbutterfly | Student, College Freshman | (Level 1) Valedictorian

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The Kerbs cycle is described as is the central metabolic pathway in all aerobic organisms, which are organism live and grow in the oxygen filled environments. The cycle is a series of eight reactions that occur in the mitochondrion.  These reactions take a two carbon molecule and completely oxidize it to carbon dioxide. 

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dori1648 | Student, Grade 10 | (Level 1) eNoter

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After glycolysis, 2 pyruvates and 2 ATP are produced. If there is oxygen present, the products go into the Krebs Cycle. The Krebs Cycle begins with a 4-carbon compound that combines with Acetyl-CoA and once they combine the CoA detaches and you now have a 6-carbon compound. From this 6-carbon compound, one carbon detaches and you know have a 5-carbon compound. This happens one more time and you will be left with a 4-carbon compound and the cycle will restart from there. Through this entire process, NAD+ is turned into NADH, ADP is turned into ATP and FAD is turned into FADH2. These products are used in the electron transport chain (the next step of cellular respiration).

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