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Krebs cycle assessment
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1) In the presence of oxygen, pyruvate is transformed into an acetyl group attached to a carriermolecule of coenzyme A. The resulting acetyl CoA can enter several pathways, but most often,
the acetyl group is delivered to the citric acid cycle for further catabolism. During the conversion
of pyruvate into the acetyl group, a molecule of carbon dioxide and two high-energy electrons
are removed. The carbon dioxide accounts for two (conversion of two pyruvate molecules) of the
six carbons of the original glucose molecule. The electrons are picked up by NAD+, and the
NADH carries the electrons to a later pathway for ATP production. At this point, the glucose
molecule that originally entered cellular respiration has been completely oxidized. Chemical
potential energy stored within the glucose molecule has been transferred to electron carriers or
has been used to synthesize a few ATPs. Pyruvate oxidation occurs after sugar is converted to
pyruvate in glycolysis. In this case, oxidation means that electrons are removed from a molecule.
Pyruvate oxidation is the connector reaction between glycolysis in the cellular cytoplasm and the
Krebs cycle in the mitochondrial matrix. Glucose enters into glycolysis and yields 2 pyruvate
molecules. These pyruvates then get converted into 2 acetyl CoA molecules.
2) For each acetyl group that enters the citric acid cycle, three molecules of NADH are produced.
Net production of NADH: Glycolysis starts with one molecule of glucose and ends with two
pyruvate (pyruvic acid) molecules, a total of four ATP molecules, and two molecules of NADH.
NADH contributes to oxidation in cell processes like glycolysis to help with the oxidation of
glucose. The energy stored in this reduced coenzyme NADH is supplied by the TCA cycle in the
process of aerobic cellular respiration and powers the electron transport process in the
membranes of mitochondria.
3) These six CO2 molecules are given off as waste gas in the Krebs cycle. They represent the six
carbons of glucose that originally entered the process of glycolysis. At the end of the Krebs
cycle, the final product is oxaloacetic acid.
4) The Krebs cycle is the second phase in cellular respiration. It occurs in the mitochondria in the
cell. The number of ATP molecules produced in the Krebs cycle is 2. A net of four ATPs was
produced from glycolysis to the Krebs cycle.
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