Fatty Acid Synthesis and Acetyl-CoA Transport

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Questions and Answers

Where does the anabolism of fatty acids take place in animals?

Cytosol (correct)

Nucleus

Chloroplast

Mitochondria

What is required for the anabolism of fatty acids?

Acetyl-CoA and NADH+H+

Malonyl-CoA and FADH2

Acetyl-CoA and malonyl-CoA (correct)

NADPH+H+ and FADH2

Where do cells with mitochondria synthesize fatty acids?

Every cell with mitochondria, but at different rates (correct)

Only in the brain

Only in adipocytes

Only in the liver

What is the source of NADPH+H+ in adipocytes?

Pentose phosphate pathway and malic enzyme Signup and view all the answers

What is the byproduct of NADPH+H+ generation in adipocytes?

Pyruvate + CO2 Signup and view all the answers

Where does the catabolism of fatty acids take place?

Mitochondria Signup and view all the answers

Where is acetyl-CoA made in nonphotosynthetic eukaryotes?

Mitochondria Signup and view all the answers

What is the cost of transporting acetyl-CoA from the mitochondria to the cytosol?

2 ATPs Signup and view all the answers

What is the net ATP cost of synthesizing one fatty acid unit?

3 ATPs Signup and view all the answers

What is the source of acetate units in fatty acid synthesis?

Malonyl-CoA Signup and view all the answers

What is the committed step in fatty acid synthesis?

The acetyl-CoA carboxylase reaction Signup and view all the answers

What is the structure of fatty acid synthase (FAS) in vertebrates?

A single polypeptide chain with 7 active sites Signup and view all the answers

What is the product of fatty acid synthesis catalyzed by FAS I?

Palmitate 16:0 Signup and view all the answers

What is the difference between FAS I and FAS II?

FAS I is a single polypeptide chain, while FAS II is a complex of separate enzymes Signup and view all the answers

Where do plants typically store fat?

In seeds, nuts, and fruits Signup and view all the answers

How much fat does a typical 70-kg human have?

15 kg Signup and view all the answers

What is the function of phospholipids in cells?

Cell membrane structure Signup and view all the answers

What is the backbone of triacylglycerides and phospholipids?

Glycerol Signup and view all the answers

Where does most glycerol 3-phosphate come from?

Glycolysis Signup and view all the answers

What enzyme is involved in the conversion of dihydroxyacetone phosphate to glycerol 3-phosphate?

Glycerol 3-phosphate dehydrogenase Signup and view all the answers

In which cells is glycerol kinase absent?

Adipocytes Signup and view all the answers

How long can a typical 70-kg human survive on stored fat?

12 weeks Signup and view all the answers

Study Notes

Acetyl-CoA Transport and Fatty Acid Synthesis

In non-photosynthetic eukaryotes, acetyl-CoA is made in the mitochondria and transported into the cytosol for fatty acid synthesis at a cost of 2 ATPs.
The total cost of fatty acid synthesis is 3 ATPs per 2C unit, which is approximately 50% of the NADPH+H+ units necessary for fatty acid biosynthesis.

Overview of Fatty Acid Synthesis

Fatty acids are synthesized in several passes, with each pass involving the reduction of a carbonyl carbon to a methylene carbon.
The acetate unit for fatty acid synthesis comes from activated malonate in the form of malonyl-CoA.

The Acetyl-CoA Carboxylase Reaction

The acetyl-CoA carboxylase reaction is the committed step in fatty acid synthesis.

Fatty Acid Synthase (FAS)

FAS I is a single polypeptide chain with 7 active sites in vertebrates, leading to a single product: palmitate (16:0).
FAS II is a separate enzyme system in plants and bacteria, producing a variety of fatty acid products (saturated, unsaturated, branched, etc.).

Synthesis of Fat (Triacylglycerides) and Phospholipids

Animals and plants store fat (triacylglycerides) for fuel.
The typical 70-kg human has approximately 15 kg of fat, which can last for 12 weeks.
Animals, plants, and bacteria make phospholipids for cell membranes.
Both molecules contain a glycerol backbone and 2 (phospholipids) or 3 (triacylglycerides) fatty acids.

Synthesis of Backbone of TAGs and Phospholipids

Most glycerol 3-phosphate comes from dihydroxyacetone phosphate (DHAP) via glycerol 3-phosphate dehydrogenase.
Some glycerol 3-phosphate is made from glycerol via glycerol kinase (minor pathway in liver and kidney, absent in adipocytes).

Catabolism and Anabolism of Fatty Acids

Catabolism of fatty acids produces acetyl-CoA and reducing power (NADH+H+, FADH2) in the mitochondria.
Anabolism of fatty acids requires acetyl-CoA and malonyl-CoA, as well as reducing power from NADPH+H+, and occurs in the cytosol in animals and chloroplasts in plants.

Fatty Acid Biosynthesis - Place of Action

Fatty acid synthesis takes place in the cytosol of every cell with mitochondria, although the rate differs between cells.

Fatty Acid Synthesis and NADPH+H+ Levels

Fatty acid synthesis occurs in cell compartments where NADPH+H+ levels are high, such as in the cytosol of animals and yeast.
Sources of NADPH+H+ include the pentose phosphate pathway and malic enzyme in adipocytes, and the pentose phosphate pathway in hepatocytes and mammary gland.

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Description

Learn about the process of fatty acid synthesis in nonphotosynthetic eukaryotes, including the transport of Acetyl-CoA from the mitochondria to the cytosol. Understand the energy cost of this process.