Short answers, pulled from the story.
Michel Eugène Chevreul coined the term acide gras, or fatty acid, in 1813 while studying the chemistry of soaps and fats. This discovery revealed that oils and fats were composed of specific chemical chains that could be isolated and named. The work transformed the understanding of biology from a study of gross anatomy to a molecular science.
Saturated fatty acids form perfectly straight chains that pack tightly together, resulting in solid fats like butter and tallow at room temperature. Unsaturated fatty acids contain one or more double bonds that introduce a geometric constraint known as a cis configuration, which forces the chain to bend and lowers the melting point. This structural difference determines whether a cell membrane remains fluid enough to function in the cold or rigid enough to maintain integrity in the heat.
Odd-chain fatty acids such as pentadecanoic acid with fifteen carbons and heptadecanoic acid with seventeen carbons are found primarily in dairy products. These molecules are biosynthesized and metabolized through pathways that differ slightly from the standard even-chain processes, possibly involving propionyl-CoA as a starter unit rather than the usual acetyl-CoA. They play specific roles in gluconeogenesis and may serve as biomarkers for metabolic health.
The outermost layer of human skin, the stratum corneum, relies on a precise mixture of free fatty acids to function as a water-impermeable barrier. This lipid matrix is composed of an equimolar mixture of ceramides, cholesterol, and free fatty acids, with saturated fatty acids of sixteen and eighteen carbons being the dominant types. The skin also exudes a blend of fatty acids, lactic acid, and pyruvic acid that is distinctive to each individual.
Fatty acids serve as the primary fuel for the body, releasing more energy per gram than carbohydrates or proteins through a process known as beta-oxidation. In the mitochondria, fatty acids are broken down into carbon dioxide and water, releasing energy captured in the form of ATP, the universal energy currency of life. This process is so efficient that fatty acids are the preferred fuel for muscular contraction and general metabolism.
Linoleic acid and alpha-linolenic acid are the two primary essential fatty acids, belonging to the omega-6 and omega-3 families respectively, and are widely distributed in plant oils. The human body has a limited capacity to convert alpha-linolenic acid into longer-chain omega-3 fatty acids such as eicosapentaenoic acid and docosahexanoic acid, which are also found in fish. These essential fatty acids are biosynthetic precursors to endocannabinoids, which possess antinociceptive, anxiolytic, and neurogenic properties.