Lipogenesis is the process by which fatty acids and triglycerides (fats) are synthesized in the body. It primarily occurs in the liver and adipose (fat) tissue.

Where does lipogenesis occur in the body?

Lipogenesis mainly takes place in the cytoplasm of liver cells (hepatocytes) and adipocytes (fat cells).

What are the key steps in lipogenesis?

The process involves: Conversion of glucose to acetyl-CoA (via glycolysis and pyruvate metabolism). Fatty acid synthesis (acetyl-CoA is converted to malonyl-CoA and then into long-chain fatty acids). Triglyceride formation, where fatty acids are esterified with glycerol.

What enzymes are involved in lipogenesis?

Acetyl-CoA carboxylase (ACC) – converts acetyl-CoA to malonyl-CoA. Fatty acid synthase (FAS) – catalyzes the synthesis of long-chain fatty acids.

What is the main substrate for lipogenesis?

The primary substrate is acetyl-CoA, which is derived from carbohydrates, specifically glucose.

What hormones regulate lipogenesis?

Insulin (stimulates lipogenesis), Glucagon and epinephrine (inhibit lipogenesis)

How does excess carbohydrate intake affect lipogenesis?

Excess carbohydrates are converted into acetyl-CoA, which drives fatty acid and triglyceride synthesis, leading to fat storage and potential weight gain.

What is the difference between lipogenesis and lipolysis?

Lipogenesis: The process of fat synthesis and storage. Lipolysis: The breakdown of stored fats into fatty acids for energy.

Can lipogenesis be reversed?

Yes, during energy deficits, stored fats undergo lipolysis to provide energy.

How does lipogenesis contribute to obesity?

Excessive lipogenesis, due to high carbohydrate and calorie intake, leads to increased fat storage, contributing to obesity.

Home

NEET Biology

Lipogenesis

It is the metabolic pathway by which fatty acids are synthesized from Acetyl-CoA. It is not simply a reversal of the steps of degradation of fatty acids (the Beta- oxidation pathway).

OR

Lipogenesis is the metabolic process through which the body synthesizes fatty acids and converts them into fat (triglycerides) for long-term energy storage. It primarily occurs in the liver and adipose (fat) tissue.

1.0Types of Lipogenesis

De Novo Lipogenesis (DNL)
This refers to the synthesis of fatty acids from non-lipid sources, mainly excess carbohydrates. These fatty acids are then stored as triglycerides in fat tissue.
Triglyceride Synthesis
Fatty acids produced or obtained from the diet are esterified with glycerol to form triglycerides, which are stored in adipose cells.

2.0Steps of Lipogenesis

1. Conversion of Carbohydrates to Acetyl-CoA

Glucose is broken down via glycolysis to form pyruvate
Pyruvate enters the mitochondria and is converted to Acetyl-CoA

2. Formation of Malonyl-CoA

Acetyl-CoA combines with CO₂ via the enzyme Acetyl-CoA Carboxylase to form Malonyl-CoA
(This is the rate-limiting step in lipogenesis)

3. Fatty Acid Synthesis

Malonyl-CoA and Acetyl-CoA are used by Fatty Acid Synthase (FAS) to form long-chain fatty acids (mainly palmitic acid)

4. Triglyceride Formation

Fatty acids are esterified with glycerol-3-phosphate to form triglycerides, stored in fat cells.

3.0The Citrate- Malate Shuttle System

The acetyl CoA is the starting material for lipogenesis.
Because acetyl CoA generated in mitochondria and lipogenesis occurs in the cytosol, the acetyl CoA must be transported to the cytosol.
It exits the mitochondria through a transport system that involves citrate ions.
The outer mitochondrial matrix is freely permeable to acetyl CoA, as well as many other substances such as citrate, malate and pyruvate.
The inner mitochondrial membrane, however, is not permeable to acetyl CoA.

Mitochondrial acetyl CoA reacts with oxaloacetate to produce citrate, which is then transported through the inner mitochondrial membrane by a citrate transported.
Once in the cytosol, the citrate undergoes the reverse reaction to its formation to regenerate the acetyl CoA and oxaloacetate with ATP involved in the Process.
The acetyl CoA so generated becomes the “Fuel” for lipogenesis; the oxaloacetate so generated reacts further to produce malate, in an NADH dependent change.
The malate reenters the mitochondrial matrix through a malate transporter and is then converted to oxaloacetate, which can then react with another acetyl CoA molecule to form citrate and the shuttle process repeats itself.

4.0ACP Complex Formation

Two simple ACP complexes are needed to start the lipogenesis process.
They are acetyl ACP, A C_{2 -}ACP and malonyl ACP a C₃- ACP.
Additional malonyl ACP molecules are needed as the lipogenesis process proceeds.
Cytosolic acetyl CoA is the starting material for the production of both of these simple ACP complexes. Acetyl ACP is produced by direct reaction of acetyl CoA with an ACP molecule.

The reaction to produce malonyl, ACP, requires two steps. The first step is a carboxylation reaction with ATP involvement.

The Chain Elongation

This reaction occurs only when cellular ATP levels are high. It is catalyzed by acetyl CoA carboxylase complex, which requires both Mn²⁺ ion and the B vitamin biotin for its activity. The malonyl CoA produced then reacts with ACP to produce malonyl ACP.

Four reactions that occur in a cyclic pattern within the multienzyme fatty acids synthase complex constitute the chain elongation process used for fatty acids.
The reactions of the first turn of the cycle, in general terms.

Step-1 Condensation

Acetyl ACP and malonyl ACP condense together to form acetoacetyl ACP.

Step-2 First Hydrogenation

The Keto group of the acetoacetyl complex, which involves the β-carbon atom, is reduced to the corresponding alcohol by NADPH.

Step - 3 Dehydration

The alcohol produced in step- 2 is dehydrated to introduce a double bond into the molecule between ɑ and 𝛃 Carbon.

Step- 4 Second Hydrogenation

The double bond introduced in step-3 is converted to a single bond through hydrogenation. As in step-2, NADPH is the reducing agent.

Differences Between Lipogenesis and β- oxidation pathway

S.No.	Oxidation	Synthesis
Reaction Site	Mitochondria	Cytosol
Enzyme Involved	Independent	Fatty acid synthase
Intermediates carrier	Coenzyme A	Acyl carrier protein
Coenzymes	FAD, NAD+	NADPH
Carbon atoms	Removed two at a time	Added two at a time

5.0Hormonal Regulation of Lipogenesis

Hormone	Effect on Lipogenesis
Insulin	Stimulates lipogenesis
Glucagon	Inhibits lipogenesis
Cortisol	Varied effect, depending on conditions
Epinephrine	Inhibits via cAMP pathways

Insulin is the primary promoter of lipogenesis, especially after a high-carbohydrate meal.

6.0Why is Lipogenesis Important?

Energy Storage: Converts excess calories into fat for future use
Thermal Insulation: Fat helps maintain body temperature
Organ Protection: Fat cushions and protects vital organs
Metabolic Regulation: Key to managing energy balance

7.0Lipogenesis and Obesity

Excessive lipogenesis, especially in sedentary individuals consuming high-carb diets, can lead to:

Increased body fat
Insulin resistance
Non-alcoholic fatty liver disease (NAFLD)
Metabolic syndrome

Lipogenesis

It is the metabolic pathway by which fatty acids are synthesized from Acetyl-CoA. It is not simply a reversal of the steps of degradation of fatty acids (the Beta- oxidation pathway).

OR

Lipogenesis is the metabolic process through which the body synthesizes fatty acids and converts them into fat (triglycerides) for long-term energy storage. It primarily occurs in the liver and adipose (fat) tissue.

1.0Types of Lipogenesis

De Novo Lipogenesis (DNL)
This refers to the synthesis of fatty acids from non-lipid sources, mainly excess carbohydrates. These fatty acids are then stored as triglycerides in fat tissue.
Triglyceride Synthesis
Fatty acids produced or obtained from the diet are esterified with glycerol to form triglycerides, which are stored in adipose cells.

2.0Steps of Lipogenesis

1. Conversion of Carbohydrates to Acetyl-CoA

Glucose is broken down via glycolysis to form pyruvate
Pyruvate enters the mitochondria and is converted to Acetyl-CoA

2. Formation of Malonyl-CoA

Acetyl-CoA combines with CO₂ via the enzyme Acetyl-CoA Carboxylase to form Malonyl-CoA
(This is the rate-limiting step in lipogenesis)

3. Fatty Acid Synthesis

Malonyl-CoA and Acetyl-CoA are used by Fatty Acid Synthase (FAS) to form long-chain fatty acids (mainly palmitic acid)

4. Triglyceride Formation

Fatty acids are esterified with glycerol-3-phosphate to form triglycerides, stored in fat cells.

3.0The Citrate- Malate Shuttle System

The acetyl CoA is the starting material for lipogenesis.
Because acetyl CoA generated in mitochondria and lipogenesis occurs in the cytosol, the acetyl CoA must be transported to the cytosol.
It exits the mitochondria through a transport system that involves citrate ions.
The outer mitochondrial matrix is freely permeable to acetyl CoA, as well as many other substances such as citrate, malate and pyruvate.
The inner mitochondrial membrane, however, is not permeable to acetyl CoA.

Mitochondrial acetyl CoA reacts with oxaloacetate to produce citrate, which is then transported through the inner mitochondrial membrane by a citrate transported.
Once in the cytosol, the citrate undergoes the reverse reaction to its formation to regenerate the acetyl CoA and oxaloacetate with ATP involved in the Process.
The acetyl CoA so generated becomes the “Fuel” for lipogenesis; the oxaloacetate so generated reacts further to produce malate, in an NADH dependent change.
The malate reenters the mitochondrial matrix through a malate transporter and is then converted to oxaloacetate, which can then react with another acetyl CoA molecule to form citrate and the shuttle process repeats itself.

4.0ACP Complex Formation

Two simple ACP complexes are needed to start the lipogenesis process.
They are acetyl ACP, A C_{2 -}ACP and malonyl ACP a C₃- ACP.
Additional malonyl ACP molecules are needed as the lipogenesis process proceeds.
Cytosolic acetyl CoA is the starting material for the production of both of these simple ACP complexes. Acetyl ACP is produced by direct reaction of acetyl CoA with an ACP molecule.

The reaction to produce malonyl, ACP, requires two steps. The first step is a carboxylation reaction with ATP involvement.

The Chain Elongation

This reaction occurs only when cellular ATP levels are high. It is catalyzed by acetyl CoA carboxylase complex, which requires both Mn²⁺ ion and the B vitamin biotin for its activity. The malonyl CoA produced then reacts with ACP to produce malonyl ACP.

Four reactions that occur in a cyclic pattern within the multienzyme fatty acids synthase complex constitute the chain elongation process used for fatty acids.
The reactions of the first turn of the cycle, in general terms.

Step-1 Condensation

Acetyl ACP and malonyl ACP condense together to form acetoacetyl ACP.

Step-2 First Hydrogenation

The Keto group of the acetoacetyl complex, which involves the β-carbon atom, is reduced to the corresponding alcohol by NADPH.

Step - 3 Dehydration

The alcohol produced in step- 2 is dehydrated to introduce a double bond into the molecule between ɑ and 𝛃 Carbon.

Step- 4 Second Hydrogenation

The double bond introduced in step-3 is converted to a single bond through hydrogenation. As in step-2, NADPH is the reducing agent.

Differences Between Lipogenesis and β- oxidation pathway

S.No.	Oxidation	Synthesis
Reaction Site	Mitochondria	Cytosol
Enzyme Involved	Independent	Fatty acid synthase
Intermediates carrier	Coenzyme A	Acyl carrier protein
Coenzymes	FAD, NAD+	NADPH
Carbon atoms	Removed two at a time	Added two at a time

5.0Hormonal Regulation of Lipogenesis

Hormone	Effect on Lipogenesis
Insulin	Stimulates lipogenesis
Glucagon	Inhibits lipogenesis
Cortisol	Varied effect, depending on conditions
Epinephrine	Inhibits via cAMP pathways

Insulin is the primary promoter of lipogenesis, especially after a high-carbohydrate meal.

6.0Why is Lipogenesis Important?

Energy Storage: Converts excess calories into fat for future use
Thermal Insulation: Fat helps maintain body temperature
Organ Protection: Fat cushions and protects vital organs
Metabolic Regulation: Key to managing energy balance

7.0Lipogenesis and Obesity

Excessive lipogenesis, especially in sedentary individuals consuming high-carb diets, can lead to:

Increased body fat
Insulin resistance
Non-alcoholic fatty liver disease (NAFLD)
Metabolic syndrome

Frequently Asked Questions

What is lipogenesis?

Where does lipogenesis occur in the body?

What are the key steps in lipogenesis?

What enzymes are involved in lipogenesis?

What is the main substrate for lipogenesis?

What hormones regulate lipogenesis?

How does excess carbohydrate intake affect lipogenesis?

What is the difference between lipogenesis and lipolysis?

Can lipogenesis be reversed?

How does lipogenesis contribute to obesity?

Join ALLEN!

Lipogenesis

1.0Types of Lipogenesis

2.0Steps of Lipogenesis

3.0The Citrate- Malate Shuttle System

4.0ACP Complex Formation

5.0Hormonal Regulation of Lipogenesis

6.0Why is Lipogenesis Important?

7.0Lipogenesis and Obesity

Table of Contents

Frequently Asked Questions

What is lipogenesis?

Where does lipogenesis occur in the body?

What are the key steps in lipogenesis?

What enzymes are involved in lipogenesis?

What is the main substrate for lipogenesis?

What hormones regulate lipogenesis?

How does excess carbohydrate intake affect lipogenesis?

What is the difference between lipogenesis and lipolysis?

Can lipogenesis be reversed?

How does lipogenesis contribute to obesity?

Join ALLEN!

Lipogenesis

1.0Types of Lipogenesis

2.0Steps of Lipogenesis

3.0The Citrate- Malate Shuttle System

4.0ACP Complex Formation

5.0Hormonal Regulation of Lipogenesis

6.0Why is Lipogenesis Important?

7.0Lipogenesis and Obesity

Table of Contents