Lipid Metabolism Overview

Lipid Metabolism Overview

• Lipids are non-polar, hydrophobic compounds that are insoluble in water but soluble in organic solvents.
• Lipids include fats, phospholipids, sterols, and others, serving as a concentrated source of energy (1g = 9.3 kcal).
• Lipids play a role in thermoregulation, absorption of fat-soluble nutrients, and as structural components of cells and subcellular components.

Classification of Lipids

• Simple lipids: acylglycerols, waxes
• Complex lipids:
  • Phospholipids: glycerophospholipids, sphingophospholipids
  • Glycolipids
• Sterols: cholesterol, hormones, vitamins, bile acids
• Lipid derivatives: eicosanoids, polyisoprenoids, ketone bodies

Fatty Acids

• Fatty acids are aliphatic carboxylic acids, typically occurring in the body as esters in natural fats and oils.
• Fatty acids usually contain an even number of carbon atoms and can be saturated or unsaturated.
• There are two types of unsaturated fatty acids: monounsaturated (one double bond) and polyunsaturated (two or more double bonds).

Glycerophospholipids

• Glycerophospholipids are amphipathic, consisting of alkyl chains with a terminal carboxyl group.
• Phospholipids are the main lipid constituents of membranes.
• Examples of phospholipids include:
  • Phosphatidylcholine (a source of choline and involved in nervous transmission)
  • Phosphatidylethanolamine (cephalin)
  • Phosphatidylserine (plays a role in apoptosis)
  • Phosphatidylinositol (involved in cell signaling)
  • Cardiolipin (diphosphatidylglycerol, a major lipid of mitochondrial membranes)

Cholesterol

• Cholesterol is a sterol, an important lipid component of cell membranes.

Fatty Acid Synthesis (Lipogenesis)

• Fatty acid synthesis occurs primarily in the liver and lactating mammary glands, and to a lesser extent in adipose tissue.
• Lipogenesis uses ATP and NADPH and is a totally cytosolic process.
• The synthesis of fatty acids involves the repeated addition of two-carbon units from malonyl-CoA to a growing fatty acid chain.
• The process is catalyzed by a multi-enzyme complex called fatty acid synthase (FAS) and involves several enzymatic reactions, including condensation, reduction, dehydration, and reduction.
• Acyl carrier protein (ACP) is a cofactor of fatty acid biosynthesis.
• Palmitic acid (16:0) is the primary end product of fatty acid synthase activity.
• Fatty acid chains can be further elongated by the addition of two-carbon units in the smooth endoplasmic reticulum (SER).
• Desaturation of fatty acid chains occurs in the SER, requiring NADH, cytochrome b5, and its FAD-linked reductase.

Learn about the characteristics, types, and functions of lipids, including their role in energy storage, thermoregulation, and cell structure.