MCAT Biochemistry Review

Chapter 11: Lipid and Amino Acid Metabolism

11.2 Lipid Mobilization

Figure 11.2. Mobilization of Triacylglycerols and Metabolism by the Liver

At night, the body is in the postabsorptive state, utilizing energy stores instead of food for fuel. In the postabsorptive state, fatty acids are released from adipose tissue and used for energy. Although human adipose tissue does not respond directly to glucagon, a fall in insulin levels activates ahormone-sensitive lipase (HSL) that hydrolyzes triacylglycerols, yielding fatty acids and glycerol. Epinephrine and cortisol can also activate HSL, as shown in Figure 11.2; we will discuss the effects of these hormones on metabolism in more detail in the next chapter. Released glycerol from fat may be transported to the liver for glycolysis or gluconeogenesis. HSL is effective within adipose cells, but lipoprotein lipase (LPL) is necessary for the metabolism of chylomicrons and very-low-density lipoproteins (VLDL). LPL is an enzyme that can release free fatty acids from triacylglycerols in these lipoproteins.

MCAT Concept Check 11.2:

Before you move on, assess your understanding of the material with these questions.

1.    What conditions and hormones promote lipid mobilization from fat stores?

2.    What is the ratio of free fatty acids to glycerol produced through lipid mobilization?