Lipids are a diverse group of organic compounds that are insoluble in water but soluble in organic solvents. They are primarily made up of carbon (C), hydrogen (H), and oxygen (O) atoms. Lipids serve various functions in biological systems, including:
- Energy Storage: They provide long-term energy storage (e.g., triglycerides).
- Structural Components: They are key components of cell membranes (e.g., phospholipids), contributing to membrane fluidity and integrity.
- Signaling Molecules: Some lipids function as hormones or signaling molecules (e.g., steroids).
- Insulation and Protection: They help insulate the body and protect organs.
In the context of the phospholipid bilayer, lipids (specifically phospholipids) arrange themselves into two layers, with hydrophilic (water-attracting) heads facing outward towards the water inside and outside of the cell, and hydrophobic (water-repelling) tails pointing inward, away from the water. This arrangement is crucial for the formation of cell membranes and their selective permeability.