unsaturated fatty acids Fatty acids are the essential
building blocks of all fats in our food supply and body,
but not all of them have beneficial results. There are
five major fatty acid types: saturated (SAFA), unsatu-
rated (UFA), monounsaturated (MUFA), polyunsatu-
rated (PUFA), and essential (EFA).
An unsaturated fatty acid is a long-chain CAR-
BOXYLIC ACIDthat contains one or more carbon CC
double bonds. They occur when all of the carbons in a
chemical chain are not saturated with hydrogen so that
the fat molecule contains one or more double bonds
and produces a fat that is fluid at room temperature.
There are three types of unsaturated fatty acids:
monounsaturated, such as oleic acid found in olive and
sesame oils that contain one double bond; polyunsatu-
rated, such as corn, soybean, and sunflower oils that
contain more than one double bond; and essential fatty
acids (EFA) that are important, although they cannot
be created in the body. They are linoleic acid (LA) and
alpha-linolenic acid (LNA).
The double bonds in a molecule of an unsaturated
fatty acid can be found in two forms known as CISand
TRANS.
Cisdouble bonds produce a kink, or a bend, of
about 30 degrees for each double bond into the back-
bone, and these can flip over to the transform under
high temperatures. Trans double bonds allow the
molecule to lie in a straight line; however, the human
body cannot convert the transform into nutrients and so
prevents the metabolic activities from converting it to the
active cisforms. This can lead to a deficiency in essential
fatty acids. The more double bonds, and therefore more
kinks, the more beneficial it is to human health. By com-
pletely changing the physical and chemical properties,
the kinks allow essential protein associations to form
more easily, thus permitting more saturated fatty acids to
disperse and interact with water or blood.
See alsoSATURATED FATTY ACID.
unsaturated hydrocarbon A hydrocarbon (organic
compound) that contains double (alkenes) or triple
(alkynes) carbon-carbon bonds.
unsaturated solution A solution that contains less
than the maximum possible equilibrium concentration
of a solute.
unstable The opposite of STABLE, i.e., the CHEMICAL
SPECIES concerned has a higher molar GIBBS FREE
ENERGYthan some assumed standard. The term should
not be used in place of REACTIVE or TRANSIENT,
although species that are more reactive or transient are
frequently also more unstable. (Very unstable chemical
species tend to undergo exothermic UNIMOLECULAR
decompositions. Variations in the structure of the related
chemical species of this kind generally affect the energy
of the TRANSITION STATESfor these decompositions less
than they affect the stability of the decomposing chemi-
cal species. Low stability may therefore parallel a rela-
tively high rate of unimolecular decomposition.)upfield SeeCHEMICAL SHIFT.urea A nitrogen-containing waste product of
metabolism. A result of the normal breakdown of pro-
tein in the liver in mammals. It is created in liver cells
from ammonia and carbon dioxide and carried via the
bloodstream to the kidneys, where it is excreted in the
urine. Urea accumulates in the body of people with
renal failure. Urea is also a synthetic source of nitrogen
made from natural gas.urease A nickel ENZYME, urea amidohydrolase cat-
alyzes the HYDROLYSISof UREAto ammonia and carbon
dioxide. The ACTIVE SITE comprises two Ni(II) ions,
bridged by a carbamate.Urey, Harold(1893–1981) AmericanPhysical chem-
ist, geophysicist Harold Clayton Urey was born in
Walkerton, Indiana, on April 29, 1893, to Rev. Samuel
Clayton Urey and Cora Rebecca Reinsehl. His early edu-
cation was in rural schools, and he graduated from high
school in 1911 and taught for three years in country
schools.
He entered the University of Montana in 1914 and
received a B.S. degree in zoology in 1917. In 1921 he
entered the University of California and received a
Ph.D. in chemistry in 1923.
In 1924 he was a fellow in Copenhagen at Profes-
sor Niels Bohr’s Institute for Theoretical Physics as the
American-Scandinavian Foundation Fellow to Den-272 unsaturated fatty acids