Easy - S12 Fatty Acid Catabolism

Fats and Triglycerides

• Dietary triglycerides, regardless of plant or animal source, are composed of three fatty acid acyl chains and one glycerol molecule.
• Fats are an important source of energy, providing about one-third of our energy needs.

Advantages of Fats over Polysaccharides

• Fatty acids carry more energy per carbon due to their higher reduction state, resulting in more electrons available for ATP production.
• Fatty acids carry less water along because they are nonpolar.

Storage Locations of Fats

• In vertebrates, fats are stored in specialized cells called adipocytes, mainly located under the skin.
• In plants, fats are stored in seeds.

Fat Biosynthesis and Degradation Pathways

• The pathways for fat biosynthesis and degradation are different and compartmentalized.

Digestion, Mobilization, and Transport of Fats

• Dietary fatty acids are absorbed in the small intestine.
• Fats are transported and absorbed quickly.

Oxidation of Fatty Acids

• Fatty acids are oxidized through β-oxidation, producing energy.
• Mono-unsaturated fatty acids require an isomerase to bypass the first enzyme of β-oxidation.

Regulation of Fatty Acid Metabolism

• High glucose levels inhibit fatty acid breakdown by preventing fatty acid entry into mitochondria.
• Malonyl-CoA, an intermediate of fatty acid synthesis, inhibits carnitine acyltransferase I, blocking fatty acid breakdown.

β-Oxidation in Plants

• Seeds are rich in fatty acids, which are used as an energy source during germination.

Ketone Bodies

• Ketone bodies are formed when acetyl-CoA is converted to acetone, producing energy.
• This occurs in diabetic patients with high glucose levels.

Glycerol from Fats

• Glycerol from fats enters glycolysis through glycerol kinase, which activates glycerol at the expense of ATP.

Fatty Acids Conversion and Activation

• Fatty acids are converted to fatty acyl-CoA in the cytoplasm through a series of reactions.
• Fatty acyl-CoA is then transported into the mitochondria for β-oxidation.

Fatty Acid Transport into the Mitochondria

• Fatty acyl-CoA is converted to fatty acyl carnitine, which is transported into the mitochondria through a series of reactions.
• Only carnitine is transported back out of the mitochondria.

Glycerol from Fats

• Glycerol gets cleaved and enters glycolysis through the action of glycerol kinase, which activates glycerol at the expense of ATP.
• Glycerol is converted into an intermediate of glycolysis (Step 4).

Fatty Acids

• Fatty acids are converted to fatty acyl-CoA in the cytosol.
• Fatty acyl-CoA is then cleaved and undergoes beta oxidation in the mitochondria.
• Palmitic acid (C16) is a dominant carbon chain fatty acid.

Fatty Acid Transport into the Mitochondria

• Fatty acid transport into the mitochondria requires the conversion of fatty acyl-CoA to fatty acyl carnitine.
• The carnitine transporter is an integral protein that replaces CoA with carnitine, allowing the fatty acid to be transported into the mitochondria.
• Only carnitine can transport fatty acids across the mitochondrial membrane.
• Small fatty acids (< 12 carbons) can diffuse freely across the mitochondrial membrane.

Beta Oxidation of Fatty Acids

• Beta oxidation of fatty acids occurs inside the mitochondria.
• Fatty acid oxidation occurs in three stages:
• Stage 1: oxidative conversion of fatty acids into acetyl-CoA, generating NADH.
• Stage 2: oxidation of acetyl-CoA into CO2 via the citric acid cycle, generating NADH and FADH2.
• Stage 3: ATP generation from NADH and FADH2 via the respiratory chain.

Hydrolysis of Fats

• Hydrolysis of triacylglycerols is catalyzed by lipases.
• Hormone-sensitive lipase is regulated by hormones glucagon and epinephrine.
• Glucagon and epinephrine increase lipolysis by releasing the second messenger cAMP, which activates hormone-sensitive lipase.
• Lipase breaks the ester bond, releasing fatty acids and glycerol from stored triacylglycerols.

Learn about the composition and role of triglycerides in our diet, including their energy conversion and advantages over polysaccharides.