Question

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1B/) Give the steps involved in utilization of ketone bodies.
TCA cycle​

Answer 1

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Our bodies comprise 3 kinds of ketone bodies:

Acetoacetate is a metabolic product of the liver. It can be converted into acetone and beta-hydroxybutyrate.

Acetone is a product of spontaneous decarboxylation of acetoacetate or the action of acetoacetate decarboxylase. It is disposed of through breath or in the urine. Acetone does not play any role in regulating metabolism.

Beta-hydroxybutyrate is not, strictly speaking, a ketone body: it is derived from acetoacetate via the action of D-beta-hydroxybutyrate dehydrogenase. It is the most abundant ketone body.

Acetoacetate and beta-hydroxybutyrate are synthesized in the mitochondrial matrix of hepatocytes. Because they traverse membranes easily, the brain, myocardial muscles, and skeletal muscles all rely on the re-conversion of these substances when glucose levels are low. Since the brain cannot use fatty acids for energy generation because the blood-brain barrier is not permeable to fatty acids, it is dependent on ketone bodies as its sole energy resource during periods of fasting. Using ketone bodies, the brain can reduce its glucose demand from an average of approximately 150g/day to 50g/day. Ketone bodies are transported to the brain via monocarboxylate transporters 1 and 2.