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Biological Roles & Categories of Lipids
Lipids serve many jobs in the cell:
- Energy storage — triglycerides store energy; fatty acids are metabolized as an energy source.
- Signaling — steroid hormones act as intracellular messengers.
- Structure — phospholipids, sphingolipids, and cholesterol are the structural components of biological (semipermeable) membranes.
- Vitamin transport — carriers for the fat-soluble vitamins A, D, E, K.
- Cushioning/insulation for organs; waxes form protective coatings (plants, ears).
Classification hierarchy:
LIPIDS
├── Fatty Acids
│ ├── Triglycerides
│ ├── Phosphoglycerides (phospholipids)
│ ├── Waxes
│ └── Sphingolipids
│ ├── Sphingomyelins
│ └── Glycolipids → Cerebrosides, Gangliosides
└── Steroids