Ketone body formation is a three-step process. At the end of the third step, the body produces acetoacetate. Acetoacetate can be reduced to form β-hydroxybutyrate. Acetoacetate can also undergo slow spontaneous decarboxylation to form acetone. These ketone bodies can be used to generate energy.

Ketone bodies utilisation

• β-hydroxybutyrate is first converted to Acetoacetate. This reaction produces the reduced cofactor ___________.
• Acetoacetate then goes through several more steps to ultimately produce two molecules of acetyl CoA which will enter the TCA cycle to help produce ATP through oxidative phosphorylation.

During starvation, glucose and fatty acids are not enough to provide energy for survival. The body uses another fuel called ketone bodies to ensure the bodies’ energy demands are met. The process of ketone body formation is known as ketogenesis. Ketogenesis is very high after few weeks of starvation.

During starvation or uncontrolled diabetes, β-oxidation happens faster than carbohydrate breakdown. A large amount of acetyl CoA is produced during β-oxidation. The entry of this acetyl CoA into the TCA cycle to make energy is dependent on the availability of oxaloacetate.

Generally, when the carbohydrate levels are low (starvation) the levels of oxaloacetate are also low as it is being used to make glucose through the gluconeogenesis pathway.

Therefore, the excess acetyl CoA is converted into ketone bodies.

How many forms of ketone bodies are found in the body?

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How many acetyl CoA units are produced by completely breaking down the 18 carbon fatty acid?

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True or False?

What is the total yield of ATP from oxidation of an 18 carbon saturated fatty acid?

[1 NADH = 2.5 ATP and 1 FADH2 = 1.5 ATP]

Don’t forget that you will need to include reduced cofactors from β-oxidation and the TCA cycle and also account for any GTP from the TCA cycle when doing this calculation.

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Which organs in the body prefer to use ketone bodies over glucose as an energy source under normal physiological conditions?

Which statement about fatty acid synthesis is incorrect?

An 18 carbon saturated fatty acid was broken down through β-oxidation.

How many rounds of β-oxidation must occur to completely break down the fatty acid?

Enter number

True or False?

Fatty acid synthesis occurs in the ________________ and uses acetyl CoA and NADPH as starting material.