Lipids are made primarily from carbon and hydrogen atoms, often including oxygen, nitrogen, sulfur, and phosphorus as well. The main building blocks of lipids are biochemical subunits called ketoacyl groups and isoprene groups. Lipids include fats, waxes, sterols, phospholipids, and others, which are mostly hydrophobic or amphiphilic molecules. Chemically, many lipids are composed of fatty acids bonded to glycerol. Fatty acids are long hydrocarbon chains with a carboxylic acid group, and they can be saturated (no double bonds) or unsaturated (with double bonds). These fatty acids bond with glycerol to form triglycerides (fats and oils) or phospholipids, which form cell membranes. Additionally, lipids can be made from isoprene units, like sterols and terpenes. In biological systems, lipids are synthesized from acetyl-CoA units through enzymatic reactions involving fatty acid synthases, producing fatty acids that are then esterified to glycerol. Other lipids like steroids are formed from isoprene units assembled into complex ring structures. In summary, lipids are primarily made of carbon, hydrogen, oxygen, and sometimes other elements, built from fatty acids and isoprene subunits that assemble into diverse structures like fats, phospholipids, and steroids.