Lipid metabolism is crucial for energy production and storage in the body. It involves breaking down fats for fuel and creating new fats when energy is abundant. This process helps maintain energy balance and provides alternative fuel sources during fasting.
Lipids play diverse roles beyond energy, including hormone production and cell membrane structure. Understanding lipid metabolism sheds light on how the body adapts to different nutritional states and maintains overall health.
Lipid Metabolism
Energy extraction from fats
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are the primary form of stored fat in the body composed of three attached to a backbone (e.g., saturated fats, unsaturated fats)
breaks down into free fatty acids and glycerol in adipose tissue stimulated by hormones such as and (adrenaline)
process breaks down fatty acids to generate energy in the of cells
Fatty acids are converted into which enters the citric acid cycle (Krebs cycle)
Each cycle of beta-oxidation produces and used in the electron transport chain to generate ATP (cellular energy currency)
Ketogenesis in energy production
produces from fatty acids in the liver when glucose availability is limited during fasting or low-carbohydrate diets (ketogenic diets)
Acetyl-CoA from beta-oxidation is converted into ketone bodies , , and
Ketone bodies serve as an alternative energy source for tissues, especially the brain which cannot directly utilize fatty acids for energy
Ketone bodies can cross the blood-brain barrier and provide energy for the brain during glucose scarcity (e.g., during prolonged fasting)
Ketone body utilization in tissues
Ketone bodies are released from the liver and transported through the bloodstream to target tissues (e.g., brain, heart, skeletal muscle)
In target tissues, ketone bodies are converted back into acetyl-CoA:
Acetoacetate is converted into acetoacetyl-CoA by the enzyme (SCOT)
Acetoacetyl-CoA is then split into two molecules of acetyl-CoA by the enzyme
Acetyl-CoA enters the citric acid cycle to generate NADH and FADH2 for ATP production via the electron transport chain
Ketone body utilization maintains energy homeostasis during periods of glucose scarcity by providing an alternative energy source for the brain and other tissues and sparing glucose for tissues that rely on it as their primary energy source
Lipogenesis process and regulation
synthesizes fatty acids and triglycerides from excess carbohydrates primarily in the liver and adipose tissue to store excess energy as triglycerides for future use
Key steps of :
Acetyl-CoA is produced from excess glucose through glycolysis and the pyruvate dehydrogenase complex
Acetyl-CoA is converted into malonyl-CoA by the enzyme (ACC)
(FAS) catalyzes the formation of (a 16-carbon fatty acid) from malonyl-CoA and acetyl-CoA
Palmitic acid undergoes elongation and desaturation to form various fatty acids (e.g., , )
Fatty acids are esterified with glycerol to form triglycerides
Regulation of lipogenesis:
stimulates lipogenesis by activating ACC and FAS
and inhibit lipogenesis by inactivating ACC and FAS
Dietary factors such as high-carbohydrate intake can promote lipogenesis
Lipid Transport and Metabolism
are complex particles that transport lipids through the bloodstream
is a crucial component of cell membranes and serves as a precursor for steroid hormones
, synthesized from cholesterol in the liver, aid in the digestion and absorption of dietary fats
are essential components of cell membranes, contributing to membrane fluidity and function