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The graphic shows the citric acid cycle. A diagram of the citric acid cycle is shown. Acetyl C o A enters the citric acid cycle and combines with a 4-carbon compound to form citric acid. During the citric acid cycle, what happens to acetyl-CoA? It enters the citric acid cycle and gains carbon dioxide to form citric acid, and gains more carbon dioxide through redox reactions to form a 4-carbon molecule. It enters the citric acid cycle and associates with a 4-carbon molecule, forming citric acid, and then through redox reactions regenerates the 4-carbon molecule. It enters glycolysis and associates with a 5-carbon molecule through redox reactions, forming another acetyl-CoA molecule. It enters the citric acid cycle and associates with a 4-carbon molecule, forming a 5-carbon compound, and then through oxidation reactions regenerates the 4-carbon molecule.

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Answer:

It enters the citric acid cycle and associates with a 4-carbon molecule, forming citric acid, and then through redox reactions regenerates the 4-carbon molecule.

Explanation:

Acetyl-CoA(2C) associates with oxalacetate(4C) to form citric acid(6C). Then through redox reactions, CO2 molecules result from decarboxylation (COOH becomes R-(R1)CH-R2). And through dehydrogenation H2 molecules are incorporated in NADH+ in FADH2, resulting in the 4-carbon molecule at the beginning (oxalacetate). That's why it's called a cycle(Kreb's cycle or citric acid cycle)

In the citric acid cycle, when acetyl-CoA enters the cycle, it associates with a 4-carbon molecule (Oxalacetate), forming citric acid, and then through redox reactions regenerates the 4-carbon molecule (Oxalacetate).

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The resumed steps of the Citric acid cycle are as follows,

1) Acetyl CoA joins an oxaloacetate molecule, which is a 4C molecule. They release the CoA group and form a 6C molecule called Citrate.

                      Acetil CoA + Oxalacetato → Citrato + CoA group

2) Citrate turns into an isomere Isocitrate

3) Isocitrate oxidates and release 1 CO₂ molecule, producing an α- ketoglutarate molecule -this is a 5C molecule-. Meanwhile, NAD+ reduces to NADH.

                    Isocitrate + NAD+ → α-cetoglutarate + CO₂ + NADH

4) α-ketoglutarate oxidates and release 1 CO₂ molecule, producing a 4C molecule, which joins a Coenzyme A producing Succinyl-CoA. Meanwhile,  NAD+ reduces to NADH.

          α-cetoglutarate + NAD+ → 4C molecule + CO₂ + NADH

          4C molecule + Coenzyme A → Succinil-CoA

5) CoA from Succinyl-CoA is substituted with a phosphate group, which then forms ATP. The final product is Succinate and ATP

       Succinyl-CoA + Phosphate group + ADP → Succinate + ATP + CoA

6) Succinate oxidizes and forms Fumarate, a 4C molecule. FAD+ forms FAHâ‚‚

                     Succinate + FAD+ → Fumarate + FADH₂

7) A water molecule and Fumarate produce Malate, which is another 4C molecule

                                Fumarate + H₂O → Malate

8) Finally, malate oxidizes and oxalacetate regenerates -the initial 4C compound-. NAD+ reduces to NADH.

                     Malato + NAD+ → Oxalacetate + NADH

So, when acetyl-CoA enters the cycle, it associates with a 4-carbon molecule (Oxalacetate), forming citric acid, and then through redox reactions regenerates the 4-carbon molecule (Oxalacetate).

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