Lipids — Structure & Function

Classes of lipids:

Fatty acids — long hydrocarbon chains; saturated (no double bonds, solid at room temp) vs. unsaturated (double bonds, liquid)

Triglycerides — glycerol + 3 fatty acids; energy storage

Phospholipids — glycerol + 2 fatty acids + phosphate head; membrane structure

Steroids — four-ring structure; cholesterol, sex hormones, cortisol

Waxes — protective coating

Cell membrane (fluid mosaic model):

Phospholipid bilayer — hydrophilic heads face outward, hydrophobic tails face inward

Proteins embedded in membrane (integral) or attached to surface (peripheral)

Cholesterol regulates membrane fluidity — prevents crystallization at low temp, prevents excessive fluidity at high temp

Membrane transport:

Passive — with concentration gradient; no energy (diffusion, osmosis, facilitated diffusion)

Active — against gradient; requires ATP (Na⁺/K⁺ ATPase pumps 3 Na⁺ out, 2 K⁺ in)

Endocytosis/exocytosis — bulk transport via vesicles

Reference:

Wikipedia: Lipid

https://en.wikipedia.org/wiki/Lipid