Lecture Notes on Lipid Metabolism

Lecture Notes on Lipids Metabolism

• Lipids are absorbed from the intestine, undergo digestion, and are metabolized to be used by the body.
• Dietary lipids (fats and complex molecules) need to be broken down for energy.
• Lipids in the body include fatty acids, triglycerides, phospholipids, ketone bodies, steroids, and their byproducts.
• Digestion begins in the mouth, continues in the stomach, and finishes in the small intestine with assistance from the pancreas and gallbladder.
• Bile salts are crucial for lipid digestion, as they help break down fats.
• Bacteria in the small intestine break down carbohydrates, creating fermentation, and proteins into putrefaction products.
• Digestion and absorption lead to the creation of new compounds (anabolism) and breakdown of compounds (catabolism)
• The process of digestion, absorption, anabolism, and catabolism is called metabolism.

Role of Liver in Lipid Metabolism

• Liver cells (hepatocytes) play a vital role in lipid metabolism.
• Fatty acid breakdown, generating ATP, is crucial for muscle function.
• Lipoproteins are produced to transport fatty acids, cholesterol, and triglycerides to cells.
• Certain triglycerides are stored in the body.
• Cholesterol is synthesized, and used to produce bile salts. (Important note: This is also a function of cholesterol.)

Fatty Acid Metabolism

• Fatty acid activation (occurs in liver, brain, adipose) involves two steps using Acetyl CoA Carboxylase.
• The activation step turns Acetyl CoA into Malonyl CoA in two stages.
• Enzymes are packaged together in a complex called fatty acid synthase (FAS).
• This contains three enzymes: acetyl transacylase, malonyl transacylase, and β-ketoacyl ACP synthase.
• Fatty acid synthesis proceeds two carbons at a time.
• Products can be modified and elongated into longer chains, or become unsaturated.
• Malonyl CoA attaches to palmitate under the action of fatty acid synthase to form stearate.
• Other molecules like CoA and NADH assist with the process.

Fatty Acid Oxidation

• Fatty acid oxidation occurs in mitochondria (except brain and red blood cells).
• Glucose is the primary energy source for brain tissue.
• Palmitoyl CoA is transferred to mitochondria for oxidation.
• There are different types of fatty acid oxidation: alpha, beta, and omega.
• Beta-oxidation is a common process.

Lipid Transport in the Blood

• Fats are transported through the blood as free fatty acids.
• Important proteins called albumin combine with free fatty acids for blood transport.
• Activation of the fatty acids involves conversion to acyl CoA molecules.
• Transfer of fatty acids into the mitochondrial matrix is aided by carnitine.
• Acyl CoA molecules use carnitine to cross the mitochondrial membranes.

Beta-Oxidation of Fatty Acids

• The breakdown of fatty acids occurs in 4-step cycles.
• There are specific enzymes that assist these cycles.
• The cycles produce ATP, FADH2, NADH, and acetyl CoA.

Energy Production from Beta-Oxidation

• The oxidation of palmitic acid (a saturated fatty acid with 16 carbons) produces significant ATP.
• Oxidation of odd chain fatty acids, though similar to beta-oxidation, forms additional molecules.
• The process is regulated and crucial in times of low glucose.

Ketone Body Metabolism

• Ketone bodies, like acetoacetate, acetone, and β-hydroxybutyrate, are produced in the liver.
• Liver mitochondria are the site of ketone body production.
• These bodies are transported to extra hepatic tissues for energy.
• The major ketone bodies produced by the body are acetoacetate, acetone, and β-hydroxybutyrate.
• These bodies are used in times of starvation or low glucose.

Triglyceride Metabolism

• Triglycerides are esters that are commonly produced in the liver and adipose tissues.
• They use glycerol-3-phosphate and acyl CoA esters for synthesis.
• An alternative route is to use dihydroxyacetone phosphate.
• Triglycerides are important compounds in storage and function as a crucial energy source.
• Triglycerides are comprised of fatty acids and glycerol, and are used by the body for energy storage.

Cholesterol Synthesis

• Cholesterol is an important sterol, and is synthesized from acetate in the liver and other tissues.
• It has a hydroxyl group, double bonds, and asymmetric carbon atoms with a side chain of 8 carbon atoms.
• It's crucial for cell membranes, steroid hormones, and Vitamin D, etc.
• The synthesis process occurs primarily in the liver and possibly in the intestine, skin, and adrenal cortex.
• The synthesis of cholesterol involves important steps and molecules.

Cholesterol Metabolism Fate

• Cholesterol is excreted through bile.
• Cholesterol is converted to bile acids.
• Cholesterol helps make steroid hormones (like testosterone and cortisol).
• Cholesterol plaques can develop in the arteries.

This quiz covers key concepts related to lipid metabolism, including digestion, absorption, and the role of the liver. Learn how dietary fats are processed in the body and understand the metabolism pathways that lead to energy production. Ideal for students studying biochemistry or related fields.