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Lipogenesis Overview & Function

Daniel Spaargaren, Rebecca Gillaspy
  • Author
    Daniel Spaargaren

    Daniel Spaargaren has an associate’s degree in Exercise Science from Three Rivers Community College and bachelor’s degree in Exercise Science from Central Connecticut State University. He was a tutor at his college for math, chemistry, and physics. He also answered student’s chemistry questions online.

  • Instructor
    Rebecca Gillaspy

    Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Explore the metabolic process of lipogenesis. Learn the definition of lipogenesis and understand the role of carbohydrates in it. See the function of lipogenesis and find where It occurs. Updated: 12/31/2021

Table of Contents


What is Lipogenesis?

Lipogenesis is the synthesis of acetyl-coenzyme A (acetyl-CoA) subunits into triglycerides. Lipogenesis consists of fatty acid synthesis followed by triglyceride synthesis. The triglycerides formed in lipogenesis are stored in the adipocytes of adipose tissue. Acetyl-CoA is the building block of fatty acids, and consists of an acetyl group bonded to the nucleotide coenzyme A. It is generated and used in different metabolic pathways, including the citric acid cycle and amino acid synthesis. Fatty acids consist of a carboxylic head group bonded to a long hydrocarbon chain. Triglycerides consist of three fatty acid residues esterified to glycerol, a three-carbon alcohol.

Acetyl-CoA structure (acetyl group is blue)

Fatty acid structure

Where Does Lipogenesis Occur?

Lipogenesis occurs mainly in the liver, adipose tissue, and small intestine, but it also occurs in other cells such as the kidneys and mammary glands. Fatty acid synthesis occurs mainly in the cytosol. Elongation of fatty acids occurs in the endoplasmic reticulum or mitochondrion. Desaturation of fatty acids occurs in the endoplasmic reticulum. Triglyceride synthesis takes place in the endoplasmic reticulum. In contrast, beta-oxidation, the degradation of fatty acids into acetyl-CoA subunits, occurs in the mitochondrion and peroxisome in animals. Lipolysis, the hydrolysis of triglycerides into fatty acids and glycerol, occurs on the surface of lipid droplets in adipocytes. It also occurs in the gastrointestinal system and in lipoproteins in the blood.

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Role of Carbohydrates in Lipogenesis

Cells can convert molecules from other metabolic pathways into triglycerides. First, the starting molecule is degraded to one of the starting materials for lipogenesis, and then lipogenesis forms triglycerides. Excess carbohydrates in the body are commonly converted into triglycerides. Polysaccharides used for lipolysis are first broken down into monosaccharides. Polysaccharides either come directly from food or are stored as glycogen in the liver and muscle tissue. Glycogenolysis is responsible for degrading glycogen to glucose (in the liver) or glucose-6-phosphate (in muscle). Polysaccharides from the diet are broken down into monosaccharides including glucose, fructose, and galactose. These monosaccharides enter glycolysis at different steps, where they are degraded to different intermediates and ultimately pyruvate. Pyruvate can then be decarboxylated to form acetyl-CoA, one of the starting materials for fatty acid synthesis. Glycolysis intermediates dihydroxyacetone phosphate and pyruvate can also be converted to glycerol-3-phosphate, one of the starting materials for triglyceride synthesis.

Function of Lipogenesis

The purpose of lipogenesis is to synthesize triglycerides that will be stored as energy in adipose tissue. These triglycerides can later be broken down via beta-oxidation to generate adenosine triphosphate (ATP). Triglycerides are the preferred energy storage molecule because the highly reduced fatty acid tails have high energy potential when oxidized. In fact, fatty acids produce over twice as much energy per gram as polysaccharides during oxidation. Triglycerides can be synthesized via lipogenesis from various starting materials, including carbohydrates, amino acids, and other lipids. These molecules are degraded through different metabolic pathways to produce the starting materials for lipogenesis, including acetyl-CoA and glycerol-3-phosphate.

Process of Lipogenesis

Lipogenesis involves fatty acid synthesis followed by triglyceride synthesis. Fatty acid synthesis begins with acetyl-CoA. Acetyl-CoA can be derived from carbohydrates, in which the final product of glycolysis, pyruvate, reacts with coenzyme A to form acetyl-CoA. It can also be derived from beta-oxidation, in which a fatty acid is broken down into acetyl-CoA subunits.

The first step of fatty acid synthesis involves transporting acetyl-CoA from the mitochondrion to the cytosol. First, citrate synthase catalyzes the condensation of acetyl-CoA and oxaloacetate to form citrate and coenzyme A. Then, citrate transport protein (CTP) transports citrate from the mitochondrion to the cytosol. ATP-citrate lyase catalyzes the conversion of citrate and coenzyme A to oxaloacetate and acetyl-CoA in the cytosol. In the cytosol, acetyl-CoA carboxylase catalyzes the carboxylation of acetyl-CoA to malonyl-CoA by consuming ATP. This is the rate-limiting step of fatty acid synthesis.

The next seven reactions involve the enzyme fatty acid synthase catalyzing the synthesis of palmitate from malonyl-CoA and an acyl group (which starts off as acetyl-CoA). Fatty acid synthase is a dimer of two identical polypeptides, and each polypeptide has six active sites that catalyze the seven reactions.

  • First, the acetyl group of acetyl-CoA is transferred to a cysteine residue on the enzyme to form an acetyl thioester group.
  • The malonyl group of malonyl-CoA is then transferred to the acyl carrier protein (ACP) domain of the enzyme, forming malonyl-ACP.
  • The acetyl group and malonyl-ACP undergo a condensation reaction to form acetoacetyl-ACP
  • Next, acetoacetyl-ACP is reduced to 3-hydroxybutyryl-ACP using nicotinamide adenine dinucleotide phosphate (NADPH).
  • 3-hydroxybutyryl-ACP is then dehydrated to butenoyl-ACP.
  • Next, butenoyl-ACP is reduced to butyryl-ACP using NADPH.
  • Finally, the butyryl group is transferred from ACP back to the cysteine residue.
  • The cycle repeats six times, forming two-carbon-longer acyl intermediates each time, to ultimately form the sixteen-carbon fatty acid palmitate.

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Frequently Asked Questions

What is the difference between lipogenesis and lipolysis?

Lipogenesis is the synthesis of triglycerides from acetyl-CoA into fatty acids which are then converted to triglycerides. Lipolysis is the degradation of triglycerides into glycerol and free fatty acids.

What is the purpose of lipogenesis?

The purpose of lipogenesis is to produce triglycerides from acetyl-CoA subunits. These triglycerides are then used as an energy reserve stored in adipose tissue.

What are the steps of lipogenesis?

Lipogenesis consists of fatty acid synthesis and triglyceride synthesis. First, fatty acids are synthesized from acetyl-CoA subunits. Then, three fatty acids are esterified to glycerol-3-phosphate to form a triglyceride.

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