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Ketone bodies are produced mainly in the mitochondria of liver cells, and synthesis can occur in response to an unavailability of blood glucose, such as during fasting. [4] Other cells, e.g. human astrocytes , are capable of carrying out ketogenesis, but they are not as effective at doing so. [ 6 ]
Ketone bodies are water-soluble molecules or compounds that contain the ketone groups produced from fatty acids by the liver (ketogenesis). [1] [2] Ketone bodies are readily transported into tissues outside the liver, where they are converted into acetyl-CoA (acetyl-Coenzyme A) – which then enters the citric acid cycle (Krebs cycle) and is oxidized for energy.
During ketosis, however, acetyl-CoA from fatty acids yields ketone bodies, including acetone, and up to ~60% of acetone may be oxidized in the liver to the pyruvate precursors acetol and methylglyoxal. [19] [4] Thus ketone bodies derived from fatty acids could account for up to 11% of gluconeogenesis during starvation.
Ketosis is a metabolic state characterized by elevated levels of ketone bodies in the blood or urine. Physiological ketosis is a normal response to low glucose availability. . In physiological ketosis, ketones in the blood are elevated above baseline levels, but the body's acid–base homeostasis is maintain
The pyruvate produced by glycolysis is an important intermediary in the conversion of carbohydrates into fatty acids and cholesterol. [34] This occurs via the conversion of pyruvate into acetyl-CoA in the mitochondrion. However, this acetyl-CoA needs to be transported into cytosol where the synthesis of fatty acids and cholesterol occurs.
d -Glucose + 2 [NAD] + + 2 [ADP] + 2 [P] i 2 × Pyruvate 2 × + 2 [NADH] + 2 H + + 2 [ATP] + 2 H 2 O Glycolysis pathway overview The use of symbols in this equation makes it appear unbalanced with respect to oxygen atoms, hydrogen atoms, and charges. Atom balance is maintained by the two phosphate (P i) groups: Each exists in the form of a hydrogen phosphate anion, dissociating to contribute ...
The brain uses these ketone bodies as fuel, thus cutting its requirement for glucose. After fasting for 3 days, the brain gets 30% of its energy from ketone bodies. After 4 days, this goes up to 75%. [6] Thus, the production of ketone bodies cuts the brain's glucose requirement from 80 g per day to about 30 g per day.
Oxidative phosphorylation contributes the majority of the ATP produced, compared to glycolysis and the Krebs cycle. While the ATP count is glycolysis and the Krebs cycle is two ATP molecules, the electron transport chain contributes, at most, twenty-eight ATP molecules. A contributing factor is due to the energy potentials of NADH and FADH 2.