Ch. 24 Chem (Lipid Metabolism)

Digestion of Triacylglycerols (Process)

• Triacylglycerols start by breaking down in the small intestine

• In the mouth and stomach, triacylglycerols are undigested in droplets

• Then, from the small intestine, they either enter bloodstream or micelles-(glycerol and soluble fatty acids enter the bloodstream, they stop here)

  (insoluble acylglycerols and fatty acids enter micelles)

• The ones that are insoluble are then packaged and delivered to cells through chylomicrons

Lipoproteins

• Consist of droplets of hydrophobic lipids surrounded by phospholipids, proteins, and other molecules with their hydrophilic ends to the outside

• They are special forms of micelles

Major bile acid

Cholic acid

Types of Lipoproteins

1. Chylomicrons

2. VLDLs (Very low density)

3. IDLs (Intermediate density)

4. LDLs (Low density, bad cholesterol)

5. HDLs (High density, good cholesterol)

Chylomicrons

• Transport dietary TAGs from small intestine to liver

• Density of less than 0.95g/cm³

VLDLs

• Transport TAGs (synthesized) from liver to tissues

• 0.96-1.006g/cm³

IDLs

• Transport remnants of VLDLs back to liver

• 1.007-1.019g/cm³

LDLs

• Transport cholesterol from liver to tissues

• 1.020-1.062g/cm³

HDLs

• Transport cholesterol from dead cells back to liver

• 1.063-1.210g/cm³

3 Sources of Lipids

1. Dietary

2. Stored (Adipose) → Serum Albumin

3. Synthesized (Liver)

Triacylglycerols Purpose

Essential for our well-being as long-term energy storage, insulation for our bodies, and cushioning for our internal organs

Mobilization (of triacylglycerols)

The hydrolysis of triacylglycerols in adipose tissue and the release of fatty acids into the bloodstream

Fatty Acid Metabolism (Oxidation)

1. Activation- Fatty Acid → Fatty Acyl- CoA

2. Transport- Fatty Acyl- CoA → Fatty Acyl-Carnitine

   → Mito Matrix

   → Fatty Acyl- CoA

3. B-Oxidation (study)

Ketogenesis

The synthesis of ketone bodies from acetyl-CoA

When more Acetyl-CoA is produced than needed

Ketogenesis → Ketone Bodies (Acetoacetate, 3-Hydoxybutyrate, Acetone) → Ketoacidosis (lowers pH)

Ketoacidosis

• Acidic conditions in the blood (dangerous)

• Can occur when diabetes is untreated

Lipogenesis

The biochemical pathway for synthesis of fatty acids from acetyl-CoA

Fatty Acid Oxidation (Traits and Comparison to Synthesis)

• Occurs in mitochondria

• Enzymes different from synthesis

• Intermediates carried by coenzyme A

• Coenzymes: FAD and NAD+

• Carbon atoms removed two at a time

Fatty Acid Synthesis (Traits and Comparison to Oxidation)

• Occurs in cytosol

• Enzymes different from oxidation

• Intermediates carried by acyl carrier protein

• Coenzyme: NADPH

• Carbon atoms added two at a time

Steps of Biosynthesis of Fatty Acids

1. Condensation

2. Reduction

3. Dehydration

4. Reduction