Chapter 22, Problem 11E

Summary Introduction

To explain: The reason for the requirement of insulin in adipocytes to synthesize triacylglycerols from fatty acids.

Concept introduction: Triglyceride (TG) or triacylglycerol is an ester that is formed from a glycerol and three fatty acids. TGs are the main constituents of the body fat in the humans and other animals. Triacylglycerol is seen in the adipocyte cells of the adipose tissue, where the fat is stored.

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Fatty acids are stored in the form of triglycerides in all the cells, but mainly in the adipocytes of the adipose tissue. Glycerol phosphate pathway is the major pathway for the biosynthesis of triacylglycerols. In adipocytes, glucose is essential for glycerol-3-phosphate, which is the backbone of the triacylglycerols. GLUT4 is an insulin-regulated glucose transporter that is found mainly in the adipose tissue and striated muscles. Insulin plays important role in hormonal control of synthesis of triacylglycerols from fatty acids in adipocytes through following functions:

• By promoting glucose uptake in the adipose tissue by increasing the GLUT4 receptors present on adipocytes.
• By activating enzyme pyruvate dehydrogenase complex
• By activating the enzyme acetyl CoA carboxylase
• By increasing the cellular levels of fatty acid synthase
• By reducing lipolysis by inhibiting insulin-sensitive lipase.