Organic compound that is an important component of lipids in
plants, animals, and microorganisms. Fatty acids are carboxylic
acids with a long hydrocarbon chain, usually straight, as the
fourth substituent group on the carboxyl (singlehorzbondCOOH)
group (see functional group) that makes the molecule an acid. If
the carbon-to-carbon bonds (see bonding) in that chain are all
single, the fatty acid is saturated; artificial saturation is
called hydrogenation. A fatty acid with one double bond is
monounsaturated; one with more is polyunsaturated. These are
more reactive chemically. Most unsaturated fats are liquid at
room temperature, so food manufacturers hydrogenate them to make
them solid (see margarine). A high level of saturated fatty
acids in the diet raises blood cholesterol levels. A few fatty
acids have branched chains. Others (e.g., prostaglandins)
contain ring structures. Fatty acids in nature are always
combined, usually with glycerol as triglycerides in fats. Oleic
acid (unsaturated, with 18 carbon a