MN10 - Fatty Acid Metabolism

What are lipids?

Lipids are a heterogeneous group of water-insoluble molecules that can be compartmentalized in membranes and adipocytes or circulate bound to proteins.

What are the main functions of lipids?

Lipids function in energy storage, structural components, metabolic regulation, cushioning and insulation, absorption of fat-soluble vitamins, and improving food taste.

What are simple lipids?

Simple lipids are esters of fatty acids with alcohols such as glycerol.

What are triacylglycerols (TAGs)?

Triacylglycerols are simple lipids composed of a glycerol backbone esterified to three fatty acids.

What are complex lipids?

Complex lipids are simple lipids with additional groups such as phosphate, carbohydrate, or sulfate.

What are examples of complex lipids?

Examples include phospholipids, glycosphingolipids, and sulfatides.

What are derived lipids?

Derived lipids are compounds of fatty acids such as cholesterol, steroids, and eicosanoids.

What are lipoproteins?

Lipoproteins are complexes of lipids bound to proteins that transport lipids in the bloodstream.

What are fatty acids?

Fatty acids are aliphatic carboxylic acids (R-COOH) that serve as a major source of energy.

How are fatty acids classified by carbon number?

Fatty acids are classified as even-chain (most common in humans) or odd-chain (more common in microbial cells).

How are fatty acids classified by chain length?

Fatty acids are classified as short (2-6 carbons), medium (8-14 carbons), or long (>16 carbons).

How are fatty acids classified by saturation?

Fatty acids are classified as saturated or unsaturated (mono- or polyunsaturated).

What is the carboxyl carbon in fatty acid nomenclature?

The carboxyl carbon is designated as carbon 1 (C1).

What is the omega (ω) carbon in fatty acids?

The omega carbon is the last carbon in the fatty acid chain, opposite the carboxyl group.

How are double bonds described in fatty acids?

Double bonds can be described by their position from the carboxyl end or from the omega (ω) end.

What does the notation 20:4(5,8,11,14) represent?

It represents a 20-carbon fatty acid with four double bonds located at carbons 5, 8, 11, and 14.

Which fatty acids are essential?

Linoleic acid (ω-6) and linolenic acid (ω-3) are essential fatty acids.

Why are some fatty acids essential?

Humans cannot introduce double bonds beyond carbon 9, so certain fatty acids must be obtained from the diet.

How is acetyl-CoA transported from mitochondria to cytosol?

Acetyl-CoA is transported via the citrate shuttle.

What happens to acetyl-CoA in the mitochondria during transport?

Acetyl-CoA combines with oxaloacetate to form citrate via citrate synthase.

What happens to citrate in the cytosol?

Citrate is cleaved into acetyl-CoA and oxaloacetate by citrate lyase.

Where does fatty acid synthesis occur?

Fatty acid synthesis occurs in the cytosol.

What is the precursor for fatty acid synthesis?

Acetyl-CoA is the precursor for fatty acid synthesis.

What is the rate-limiting enzyme of fatty acid synthesis?

Acetyl-CoA carboxylase (ACC) is the rate-limiting enzyme.

What reaction does acetyl-CoA carboxylase catalyze?

It converts acetyl-CoA to malonyl-CoA.

What cofactors are required for acetyl-CoA carboxylase?

Biotin and ATP are required.

How is ACC regulated allosterically?

ACC is activated by citrate and inhibited by palmitoyl-CoA.

How is ACC regulated by phosphorylation?

Phosphorylation by AMP, glucagon, and epinephrine inactivates ACC.

How does insulin regulate ACC?

Insulin promotes dephosphorylation and activation of ACC.

How is ACC regulated long-term?

High glucose and insulin increase ACC gene expression.

What is fatty acid synthase (FAS)?

Fatty acid synthase is a multicatalytic homodimer enzyme complex with seven enzymatic domains per monomer.

How does fatty acid synthase elongate fatty acids?

It adds two-carbon units in a cyclic series of condensation and reduction reactions.

What is the final product of fatty acid synthesis?

Palmitate, a 16-carbon saturated fatty acid, is the final product.

What is the storage form of fatty acids?

Fatty acids are stored as triacylglycerols (TAGs).

Where are TAGs synthesized?

TAGs are synthesized in the liver and adipose tissue.

What is the structure of a triacylglycerol?

A triacylglycerol consists of glycerol esterified with three fatty acids.

What is the initial acceptor of fatty acids in TAG synthesis?

Glycerol-3-phosphate is the initial acceptor.

What is the activated form of fatty acids for TAG synthesis?

Fatty acids are activated as fatty acyl-CoA.

How are TAGs formed from fatty acids?

Three fatty acyl-CoA molecules are added to glycerol-3-phosphate to form TAG.

What happens to TAG in the fed state?

In the fed state, TAGs are broken down by lipoprotein lipase, and fatty acids enter adipocytes for storage.

How does insulin affect TAG metabolism?

Insulin activates lipoprotein lipase and promotes fat storage in adipose tissue.

What happens to TAG during fasting?

During fasting, TAGs are broken down into fatty acids and glycerol by hormone-sensitive lipase.

How does glucagon affect TAG metabolism?

Glucagon activates hormone-sensitive lipase via phosphorylation, promoting lipolysis.

What happens to glycerol released from TAG breakdown?

Glycerol is transported to the liver for gluconeogenesis.

How are fatty acids transported in the blood during fasting?

Fatty acids are transported bound to albumin.

Where does β-oxidation occur?

β-oxidation occurs in the mitochondria.

How are long-chain fatty acids transported into mitochondria?

They are transported via the carnitine shuttle.

What is the first step before fatty acid transport into mitochondria?

Fatty acids are activated to fatty acyl-CoA in the cytosol.

What enzyme transfers fatty acids to carnitine?

Carnitine acyltransferase I transfers the fatty acyl group to carnitine.

What determines the melting point of fatty acids?

Melting point depends on chain length and degree of saturation.

How do saturated fatty acids affect melting point?

Saturated fatty acids pack tightly, increasing melting point and making them solid at room temperature.

How do unsaturated fatty acids affect melting point?

Unsaturated fatty acids do not pack tightly, lowering melting point and making them liquid at room temperature.