Fatty Acid Synthesis Mechanisms

Questions and Answers

What is the primary function of the microsomal pathway in fatty acid elongation?

To activate fatty acids into fatty acyl CoA

To elongate existing long-chain fatty acid molecules (correct)

To produce fatty acids shorter than 16 carbons

To synthesize triacylglycerols from fatty acids and glycerol

What molecule acts as the acetyl donor in the microsomal pathway of fatty acid elongation?

Glycerol-3-phosphate

Malonyl CoA (correct)

Dihydroxyacetone phosphate

Palmitate

During myelination of nerves, which fatty acid lengths are primarily produced by the microsomal pathway?

C10-C16

C26-C28

C18-C20

C22-C24 (correct)

What is the main function of glycerol-3-phosphate in lipogenesis?

It provides the glycerol backbone for triacylglycerol synthesis Signup and view all the answers

What is the primary role of insulin in lipogenesis?

It stimulates glycolysis, leading to increased dihydroxyacetone phosphate production Signup and view all the answers

Which hormone is primarily responsible for inhibiting lipogenesis and stimulating lipolysis during fasting?

Glucagon Signup and view all the answers

In which tissue(s) is lipogenesis primarily regulated by the interplay of insulin and glucagon?

Liver and adipose tissue Signup and view all the answers

What is the primary cause of fatty liver disease?

Imbalance between triacylglycerol synthesis and export Signup and view all the answers

What is the main product of the cytoplasmic pathway of fatty acid synthesis?

Palmitate (16C) Signup and view all the answers

What enzyme is key in regulating the cytoplasmic pathway of fatty acid synthesis?

Acetyl CoA carboxylase Signup and view all the answers

Which of the following conditions inhibits fatty acid synthesis?

Increased glucagon levels Signup and view all the answers

What is formed when acetyl CoA is activated during fatty acid synthesis?

Malonyl CoA Signup and view all the answers

Where does fatty acid synthesis take place within the cell?

Cytosol Signup and view all the answers

Which of the following substrates is NOT required for fatty acid synthesis?

Glycerol Signup and view all the answers

What role does citrate play in fatty acid synthesis?

Stimulator of acetyl CoA carboxylase Signup and view all the answers

What are the main reactions involved in fatty acid synthesis?

Condensation, Reduction, Dehydration, and Reduction Signup and view all the answers

Study Notes

Fatty Acid Synthesis

There are two mechanisms for fatty acid synthesis: cytoplasmic and microsomal.
The cytoplasmic system (extra-mitochondrial) or de novo pathway produces palmitate (16C) as its main product.
This pathway takes place in the cytosol of many tissues, including the liver, adipose tissue, lung, and kidney.
It requires acetyl CoA, NADPH+H, and a group of enzymes called fatty acid synthase complex.

Fatty Acid Synthesis Pathway

Stage 1: Transport of acetyl CoA out of the mitochondria into the cytoplasm via citrate, which is cleaved into oxaloacetate and acetyl CoA.
Stage 2: Activation of acetyl CoA to form malonyl CoA.
Stage 3: Repetitive addition and reduction of two-carbon units to synthesize C16 fatty acid on an acyl carrier protein.

Regulation of Fatty Acid Synthesis

Insulin stimulates fatty acid synthesis.
Glucagon and epinephrine inhibit fatty acid synthesis through cyclic AMP and stimulate lipolysis.
Long-chain acyl CoA inhibits fatty acid synthesis.
Citrate stimulates fatty acid synthesis through stimulation of acetyl CoA carboxylase.

Microsomal Pathway

This pathway is responsible for the elongation of existing long-chain fatty acid molecules (C10-C16) derived from palmitate and dietary fatty acids.
It requires malonyl CoA as an acetyl donor and NADPH+H as a coenzyme.
This system is active during myelination of nerves, providing C22 and C24 fatty acids for sphingolipids.

Lipogenesis

Lipogenesis is the synthesis of triacylglycerols from fatty acids (acyl CoA) and glycerol (glycerol-3-phosphate).
Steps:
- Activation of fatty acids into fatty acyl CoA.
- Synthesis of glycerol phosphate in liver, kidney, intestine, and muscle.
- Synthesis of triacylglycerol by reaction between acyl CoA and glycerol phosphate.

Regulation of Lipogenesis

After a meal, lipogenesis is stimulated by insulin, which stimulates glycolysis, providing dihydroxyacetone phosphate that is converted into glycerol phosphate in adipose tissue.
During fasting, lipogenesis is inhibited by anti-insulin hormones (e.g., glucagon), which inhibit lipogenesis and stimulate lipolysis.

Fatty Liver

Fatty liver disease is a build-up of fats in the liver, which can damage the organ and lead to serious complications.
Normally, liver cells contain only 5% of fats.
Fatty liver is formed when fat levels increase above 5% in liver cells due to an imbalance in the rate of triacylglycerol synthesis and export.