Lipid Metabolism and Fatty Acid Synthesis

Lipid Metabolism Overview

• Lipids are non-polar, hydrophobic compounds that are insoluble in water but soluble in organic solvents
• Lipids are synonymous with "fat" and include phospholipids, sterols, and others

Functions of Lipids

• Concentrated sources of energy (1g = 9.3 kcal)
• Involved in thermoregulation
• Enable absorption of fat-soluble nutrients (e.g., sterols, vitamins)
• Structural elements of cell and subcellular components
• Components of lipoproteins, hormones, and prostaglandin synthesis
• Act as electrical insulators in myelinated nerves

Classification of Lipids

• Simple: Acylglyceroles, Waxes
• Complex: Phospholipids, Glycolipids, Sterols
• Lipid Derivatives: Eicosanoids, Polyisoprenoids, Ketone bodies

Fatty Acids

• Aliphatic carboxylic acids
• Occur in the body mainly as esters in natural fats and oils
• Can be saturated or unsaturated
• Typically contain an even number of carbon atoms
• Monounsaturated fatty acids: contain one double bond
• Polyunsaturated fatty acids: contain two or more double bonds

Fatty Acid Synthesis (Lipogenesis)

• Occurs primarily in the liver and lactating mammary glands
• Uses ATP and NADPH
• Totally cytosolic process
• Insulin activates ACC, while glucagon inhibits ACC

Synthesis of Fatty Acids

• Palmitic acid (16:00) synthesis occurs through a series of reactions
• Involves the repeated addition of two-carbon units from malonyl-CoA to a growing fatty acid chain
• Catalyzed by fatty acid synthase (FAS) and acyl carrier protein (ACP)
• Each cycle adds two carbons to the growing fatty acid chain
• Typically around 7 cycles are performed

Elongation of Fatty Acid Chains

• Palmitate can be further elongated by the addition of two-carbon units in the smooth endoplasmic reticulum (SER)
• Acyl-CoA or Malonyl-CoA molecules serve as the starting point for elongation
• NADPH supplies the electrons
• The brain has additional elongation capabilities, allowing it to produce very-long-chain fatty acids

Desaturation of Fatty Acid Chains

• Enzymes (desaturases) present in the SER are responsible for desaturating long-chain fatty acids
• Desaturation reactions require NADH, cytochrome b5, and its FAD-linked reductase

This quiz covers the overview of lipids, their properties, functions, and synthesis. It includes topics such as protoplasmic and reserve lipids, energy sources, and thermoregulation.