Question

17. Hibernating bears rely on triacylglycerols as their primary energy source for approximately seven months of the year.
(a) Describe why this could lead to keto-acidosis, mentioning specifically the intermediate acetyl-
CoA.

Answer 1

Triacylglycerols can be broken down into glycerol & fatty acids. When free carbohydrates are not available as in case of fasting, the body utilizes the stored fat (triacylglycerol) as fuel. The fatty acids are broken down in a process called beta -oxidation yielding acetyl-CoA. Under normal conditions, acetyl-CoA enters the TCA cycle where it is oxidized to produce energy. However, in the absence of glucose, oxaloacetate is not available as it enters gluconeogenesis (first step in TCA cycle: acetyl CoA + oxaloacetate-------------.citrate). Thus, acetyl-CoA build up.

Acetyl-CoA trigger ketogensis. The ketone bodies synthesized from acetyl-CoA include acetoacetate, beta-hydroxybutyrate &acetate. Acetoacetate &beta hydroxy butyrate are acidic and if the levels of these ketone bodies are high in blood, pH of blood drops resulting in keto-acidosis.Therefore metabolism of triacylglycerol asprimary energy source may result in keto-acidosis.