LIPIDS

Based on Saponification
- A. Saponifiable Lipids: Can be hydrolyzed in alkaline conditions to yield salts of fatty acids.
  - Examples: triacylglycerols, phospholipids, sphingolipids, sphingoglycolipids, biological waxes.
- B. Nonsaponifiable Lipids: Do not undergo hydrolysis.
  - Examples: cholesterol, steroid hormones, bile acids, eicosanoids.
Based on Biochemical Function
- Energy-storage Lipids: e.g., triacylglycerols
- Membrane Lipids: e.g., phospholipids, sphingolipids, cholesterol
- Emulsification Lipids: e.g., bile acids
- Messenger Lipids: e.g., steroid hormones, eicosanoids
- Protective-coating Lipids: e.g., biological waxes

Basic building blocks exist but due to diversity, multiple building blocks are required.
Principal Structural Unit: Fatty acids are the foremost building blocks, primarily in energy-storage and membrane lipids.

Fatty acids are naturally occurring monocarboxylic acids, typically containing an even number of carbon atoms.
Characterized by Length:
- Long-chain: 12 to 26 carbon atoms
- Medium-chain: 8 to 10 carbon atoms
- Short-chain: 4 to 6 carbon atoms
Fatty acids are rarely free in nature, forming part of complex lipid molecules.

Storage Location: Primarily in adipocytes under the skin, abdominal cavity, and other organs.
More efficient at storing energy than glycogen, the most abundant type of lipid in the human body.
Functional Groups: Triacylglycerols are triesters, containing three ester functional groups formed from glycerol and three fatty acids.

Structural representations include block diagrams and general structure formulas.

Involves protonation, nucleophilic addition, proton transfer, elimination, and production of ester from glycerol and fatty acids.

Formed by the esterification of three fatty acids to glycerol.
- Simple Triacylglycerol: Uses three identical fatty acids.
- Mixed Triacylglycerol: Uses different fatty acids, the more biochemically significant variant.

Dietary fat, encompassing both fats and oils, impacts bodily reactions. Recommended intake limits total fat to 30% of total calories.
Good sources of monounsaturated fatty acids include olive, avocado, and canola oils.

Cold-water fish offers a higher omega-3 fatty acid content compared to leaner, warm-water fish.
Omega-3 fatty acids originate in algae, which fatty fish consume.

Necessary for human health and not synthesized in adequate amounts within the body:
- Linoleic Acid: Precursor for eicosanoids, essential for blood pressure regulation.
- Linolenic Acid: Sources for EPA and DHA, vital for brain communication and normal development.

Simplesse: Calorie-reduced fat substitute made from egg whites and milk, mimics the texture of fat with lower calories (1.3 cal/g).
Olestra: Calorie-free fat substitute derived from sucrose and fats, cannot be digested and may interfere with nutrient absorption leading to gastrointestinal issues.

Reverse of esterification, requiring acid/base presence to yield glycerol and free fatty acids or salts.

Hydrolysis performed in an alkaline solution, yielding glycerol and fatty acid salts; historically used in soap-making.

Addition process that alters saturation levels of fatty acids, impacting melting points, often utilized in food products.

Causes rancidity in fats; antioxidants like BHA, BHT, Vitamin C, and Vitamin E are employed to prevent this.

Comprising 80% of cell membrane mass, major lipid types include phospholipids, sphingolipids, and cholesterol.

Most abundant type, characterized by fatty acid, phosphate, and alcohol components, critical for membrane structure.

A vital component of membranes and a precursor for other sterilized lipids, important in regulating membrane fluidity.

Lipid bilayers play a crucial role in cellular structure, permeability, and signaling. Membrane proteins are essential for transport and cell communication.

The diversity and complexity of lipids contribute to their essential roles in biological membranes, energy storage, hormonal functions, and overall human health.