Ch. 17 – Lipids
Fats and oils belong to the class of biomolecules called lipids.
Lipids serve as an energy source or for energy storage (most energy
stored in the body is stored in this form), are hormones, are
important components of brain and neural tissue, serve as
protective insulation for our vital organs, are fat-soluble vitamins (A,
D, E, K), and compose cell membranes (phosphoglycerides,
sphingolipids, and steroids).
Unlike carbohydrates which were categorized by functional group,
lipids are classified by solubility, as they are generally insoluble in
O, but soluble in nonpolar organic solvents like hexane, acetone,
A general formula for lipids cannot be written. They are
subdivided into four main groups: 1) fatty acids, 2) glycerides, 3)
nonglyceride lipids, 4) complex lipids.
Carboxylic acids (fatty acids) are found as key components in fats
and oils, typically contain an even # of C atoms, & are generally
Fatty acids are classified by the presence and # of C=C bonds.
Saturated fatty acids – contain no
C=C bonds (see top of Table 17.1,
Monounsaturated fatty acids – contain one
Polyunsaturated fatty acids – contain 2 or more C=C bonds
Typically unsaturated fatty acids have lower melting points than
saturated fatty acids (which are relatively straight and stack closely in a
matter for fatty acids?
Inexpensive and abundant vegetable oils (cottonseed, corn,
soybean) are converted to oleomargarine and semisolid cooking fats
by partial hydrogenation (reaction with H
with Ni catalyst).
would be better off using the original vegetable oils, but we prefer
the physical consistency and texture of oleo to use of a liquid oil.
Most people now try to avoid a diet high in saturated fats (often
from animals), which along with cholesterol, will predispose one to
the coronary disease arteriosclerosis (hardening of the arteries).
Many people switched to margarine to avoid saturated fats, but the