Final answer:
Ketone bodies, consisting of acetoacetate, beta-hydroxybutyric acid, and acetone, are produced in the liver from Acetyl-CoA and are used by other tissues as an alternative energy source, particularly when glucose is scarce.
Step-by-step explanation:
Ketone bodies are primarily produced in the liver from Acetyl-CoA, which is a product of the beta-oxidation of fatty acids. This process occurs when there is an excess of acetyl-CoA that the citric acid cycle cannot fully utilize, leading to the formation of acetoacetate, beta-hydroxybutyric acid, and acetone. These ketone bodies are collectively known as 'acetone bodies'. The synthesis process is known as ketogenesis. Besides fatty acids, glucose and amino acids can also provide Acetyl-CoA for ketone body production.
Ketone bodies serve as an alternative energy source for certain organs, such as the brain and heart, especially when glucose supply is low, like in prolonged starvation. The liver cannot utilize ketone bodies due to the lack of certain activating enzymes. Instead, they are transported to peripheral tissues for metabolism. The primary ketone body, beta-hydroxybutyrate, along with acetoacetate, can be converted back to Acetyl-CoA and enter the citric acid cycle to produce energy for these tissues.