of thousands of atoms held together by covalent bonds. Below four
fundamental types of biological molecules are described: lipids, pro-
teins, carbohydrates, and nucleic acids.
The fats or lipids (Greek lipos = fat) are medium-size molecules
composed primarily of carbon and hydrogen atoms in long chains,
generally sixteen to twenty-four carbon atoms long. Often there are
a few oxygen atoms at one end of the chain of carbons. The roles of
these molecules within cells are diverse and include energy storage
(lots of energy is contained in the carbon-carbon and carbon-hydro-
gen bonds within the molecule), signaling within and between cells,
precursor molecules the cell uses to make certain neurotransmitters
and hormones, and formation of membranes enclosing cells and its
interior structures.
A fatty acid is a kind of lipid molecule consisting of a hydrocarbon
chain with a carboxylic acid group (-COOH) at one end. Palmitic acid is
a sixteen-carbon fatty acid. It is called a saturated fatty acid because
all the carbons are fully bonded with hydrogen atoms; there are no
double bonds. Palmitic acid is very common in plants and animals.
It draws its name from palm trees and is a major component in palm
oils.
OPg Pica ALOR L OT aay
Palmitic acidAnother example of a lipid molecule is oleic acid, an eighteen-
carbon fatty acid. Its name comes from oleum, Latin for “oil.” The
chemical composition of olive oil is more than 50 percent oleic acid.
Oleic acid contains one double bond, and thus is an unsaturated (mo-
nounsaturated) fatty acid. The double bond is located nine carbons in