By Hayley Ames – Updated Mar 24, 2022
All lipids are composed of the same three atoms: carbon (C), hydrogen (H), and oxygen (O). While they share these elements with carbohydrates, lipids contain a higher proportion of carbon and hydrogen atoms and a lower proportion of oxygen. This imbalance—rich in C‑H bonds—makes lipids exceptionally energy‑dense, which is why they serve as primary energy stores in organisms.
Lipids are amphipathic, meaning each molecule has both a hydrophilic (water‑friendly) head and a hydrophobic (water‑repelling) tail. This dual nature allows them to self‑assemble into bilayers, forming the structural basis of cell membranes, while also providing insulation and energy storage. Lipids include fats, waxes, oils, and steroids, each with distinct roles in physiology.
Fatty acids are linear chains of carbon atoms (typically 12–24) bound to hydrogen. If every carbon-carbon bond is saturated with hydrogen, the fatty acid is saturated and has the maximum possible hydrogen content. Unsaturated fatty acids contain one to six carbon-carbon double bonds, each separated by at least two single bonds. These double bonds introduce kinks that reduce packing efficiency, lowering the melting point and increasing fluidity.
Phospholipids are unique because they possess a hydrophilic phosphate group attached to two hydrophobic fatty acid tails. This structure enables them to dissolve in both oil and water, acting as emulsifiers (e.g., lecithin). Their amphipathic nature is crucial for forming lipid bilayers that constitute cellular membranes and for mediating signal transduction.
Isoprene‑based lipids arise from the five‑carbon isoprene unit, often found in essential oils extracted via steam distillation. Multiple isoprene units can fuse to form complex structures such as steroids—cholesterol, estrogen, and testosterone—which play vital roles in hormone signaling and membrane integrity.
