Difference Between Lipolysis and Lipogenesis

Key Difference – Lipolysis vs Lipogenesis
 

Synthesis of triglycerides and fatty acids from acetyl coenzyme A is known as lipogenesis. Lipolysis is the breakdown process of triglycerides to form fatty acids. The key difference between Lipolysis and Lipogenesis is the process. Lipolysis is the hydrolysis of fats and other lipid molecules into fatty acids whereas Lipogenesis is the synthesis of fatty acids and triglyceride from acetyl coenzyme A and other substrates.

Fats are more compact energy storing molecules and contain twice as energy stored in carbohydrates. Besides the energy storage, fats provide diverse functions within the body including structural value, acting as chemical precursors, providing protective and insulating functions, etc. Fats are composed of three fatty acid molecules attached to a glycerol molecule. Hence, fat is also known as triglyceride. Triglycerides are stored in adipose tissue.

CONTENTS

1. Overview and Key Difference
2. What is Lipolysis
3. What is Lipogenesis
4. Similarities Between Lipolysis and Lipogenesis
5. Side by Side Comparison – Lipolysis vs Lipogenesis in Tabular Form
6. Summary

What is Lipolysis?

The concentration of fatty acid in cells is well controlled since unbalanced fatty acid concentration can cause several diseases such as type 2 diabetes, etc. Lipolysis is one of the cellular processes that break down fats (triglycerides) into free fatty acids and glycerol molecules. Lipolysis is driven by lipase enzymes. It is a hydrolysis process. Three ester linkages between three fatty acid molecules with glycerol molecule will break down during the lipolysis by releasing free fatty acid molecules and a glycerol molecule.

Complete hydrolysis of a triglyceride molecule is done by three lipases namely, adipose triglyceride lipase, hormone-sensitive lipase, and monoacylglycerol lipase. Triglyceride molecule is hydrolyzed into diacylglycerol by adipose triglyceride lipase releasing one non-esterified fatty acid molecule. Diacylglycerol is hydrolyzed into monoacylglycerol by hormone-sensitive lipase releasing another non-esterified fatty acid molecule. Monoacylglycerol is hydrolyzed into glycerol and non-esterified fatty acid by monoacylglycerol lipase by completely hydrolyzing the triglyceride molecule.

Figure 01: Lipolysis

The produced free fatty acid and glycerol molecules are released into the blood. Lipolysis is stimulated by series of hormonal changes that occur within the body. Reduced level of plasma insulin and glucose trigger the lipolysis. And also a high level of catecholamines, growth hormone and glucocorticoids favor the lipolysis.

What is Lipogenesis?

Lipogenesis is the process of synthesizing fatty acids and triglycerides from precursor molecules such as amino acids, sugars, PGAL, etc. Lipogenesis takes place in adipose tissue as well as in liver. Lipogenesis is controlled by many factors including hormones. Polyunsaturated fatty acids, growth hormone, leptin, and fasting inhibit the fat synthesis. It is stimulated by carbohydrate-rich diets and insulin.

Figure 02: Structure of a Lipid Molecule

Lipogenesis starts with the formation of diacylglycerol from fatty acid acyl-coenzyme A. Then the process continues by adding two more fatty acid molecules to form triglyceride molecule. Glycerol phosphate pathway, monoacylglycerol pathway, and glyceroneogenesis are the three pathways which produce diacylglycerol for lipogenesis. The synthesis of triglyceride molecule from diacylglycerol is catalyzed by two enzymes namely acyl-CoA diacylglycerol acyltransferase 1 and 2.

What are the Similarities Between Lipolysis and Lipogenesis?

• Both Lipolysis and Lipogenesis are two processes that describe lipomobilization in the body.
• Both occur in adipocytes.
• Both are associated with lipotoxicity.
• Both Lipolysis and Lipogenesis are regarding fatty acids.
• Both processes involve glycerol and triglycerides.
• Lipolysis and Lipogenesis are tightly controlled cellular processes.

What is the Difference Between Lipolysis and Lipogenesis?

Summary – Lipolysis vs Lipogenesis

Fat build-up depends on the balance between two processes namely lipogenesis (fat synthesis) and lipolysis (fat breaks down). Lipolysis releases fatty acid molecules from triglycerides by enzymatic hydrolysis. Lipogenesis synthesizes triglycerides and fatty acids molecules from acetyl coenzyme A and other precursors. Both processes occur in adipose tissue and also in the liver. This is the difference between lipolysis and lipogenesis.

Reference:

1.Kersten, Sander. EMBO Reports, Oxford University Press, 15 Apr. 2001. Available here
2.Ward, Colin. “Lipolysis and Lipogenesis.” Metabolism, Insulin and Other Hormones – Diapedia, The Living Textbook of Diabetes. Available here

Image Courtesy:

1.’Metabolism1’By Cruithne9 – Own work, (CC BY-SA 4.0) via Commons Wikimedia
2.’Fat triglyceride shorthand formula’By Wolfgang Schaefer (Public Domain) via Commons Wikimedia 

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