Untitled Quiz

Fatty Acid Catabolism and Ketogenesis

• Fats come from dietary intake, stored lipids, and synthesis.
• Dietary triglycerides (TAGs) account for over 40% of energy needs in industrialized countries, but guidelines recommend 30%.
• Resting skeletal muscle relies heavily on TAGs for energy (over 50% of energy).
• Liver and heart primarily use TAGs for energy (80%).
• Fatty acids store more energy per carbon than carbohydrates due to higher reduction.
• Fatty acids require less water for storage, making them lighter.
• Fat storage is primarily in adipocytes.

Lipolysis

• Lipolysis is the breakdown of triglycerides (TAGs) into fatty acids for further oxidation.
• Adipocytes are the primary site of lipolysis.
• Lipolysis is triggered by hormones like glucagon and epinephrine, activating a cascade of reactions.
• This cascade eventually activates hormone-sensitive lipase, leading to the release of fatty acids.
• The free fatty acids travel to the bloodstream, bound to serum albumin.
• Three enzymes are needed to break down triglycerides: adenylyl cyclase, adipose triacylglycerol lipase, and monoacylglycerol lipase.

Glycerol Metabolism

• Glycerol from fats contributes a small percentage of energy (around 5%).
• Glycerol is transported to the liver where it's primarily used for gluconeogenesis.
• Glycerol can also be stored in muscle tissue.

Fatty Acid Transport into Mitochondria

• Fatty acids need activation before entering mitochondria.
• Activation involves adding a CoA group via fatty acyl-CoA synthetase.
• Acyl-carnitine/carnitine translocase transports activated fatty acids into the mitochondrial matrix.

β-Oxidation

• Beta-oxidation is the primary process for fatty acid breakdown within the mitochondria.
• This process breaks down fatty acids into two-carbon acetyl-CoA molecules.
• The process involves four repeating steps: dehydrogenation, hydration, dehydrogenation, and thiolysis.
• Each round of beta-oxidation reduces the carbon chain by two carbons, generating one FADH2 and one NADH+H+ and one Acetyl-CoA for every round.
• After full B-oxidation, the Coenzyme A is removed, and the remaining carbon chain is ready to be used in the citric acid cycle.
• The number of rounds depends on the length of the carbon chain.

Oxidation of Unsaturated Fatty Acids

• Unsaturated fatty acids have double bonds that require isomerase and reductase.
• Monounsaturated fatty acids have one cis double bond and require one additional enzyme.
• Polyunsaturated fatty acids have more than one double bond and require both isomerase and reductase enzymes.

Oxidation of Odd-Numbered Fatty Acids

• Odd-numbered fatty acids produce propionyl-CoA, which needs conversion to succinyl-CoA before entering the citric acid cycle..

ω-Oxidation

• ω-oxidation occurs in the endoplasmic reticulum.
• ω-oxidation is an alternative pathway for fatty acid breakdown, particularly important when other pathways are impaired..

Ketogenesis

• Ketogenesis occurs in the liver mitochondria when carbohydrates are scarce.
• It converts acetyl-CoA (produced from fatty acid oxidation) into ketone bodies: acetone, acetoacetate, and D-β-hydroxybutyrate.
• These ketone bodies are exported to other tissues for energy.
• Ketogenesis is particularly important for the brain during periods of low glucose availability.