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CASE FILES: BIOCHEMISTRY
Table 41-1
ESSENTIAL AND NONESSENTIAL AMINO ACIDS
NONESSENTIAL AMINO ACIDS
(can be synthesized in the body)
ESSENTIAL AMINO ACIDS
Synthesized
Synthesized from an
(must be obtained from the diet)
from Glucose
Essential Amino Acids
Histidine
Alanine
Tyrosine
Isoleucine
Arginine
Leucine
Asparagine
Lysine
Aspartate
Methionine
Cysteine
Phenylalanine
Glutamate
Threonine
Glutamine
Tryptophan
Glycine
Valine
Proline
Arginine
+
Serine
iRequired for growth
There is a continuous need for amino acids for protein synthesis, energy
utilization, and the production of biologic mediators. The most readily
available source of all amino acids, but particularly the essential amino acids,
is the diet. Protein is taken in through the diet and digested to smaller peptides
and amino acids in the stomach and small intestine by specific proteolytic
enzymes known as proteases. Because of their different specificities, enzymes
work to cleave specific peptide bonds within proteins. Individual digestive
enzymes are not capable of completely digesting proteins themselves, but in
concert with many different enzymes, most proteins can be efficiently
digested. Once released by the digestive enzymes, amino acids are absorbed
by epithelial cells of the small intestine for distribution and utilization through-
out the body.
Composition of the diet is an important consideration when trying to under-
stand and plan for the uptake of essential amino acids. Not all dietary con-
stituents are equal with regard to the type and amounts of proteins present or
the amino acids that can be derived from these proteins by the human diges-
tive tract. Proteins derived from vegetable matter may not contain all the
essential amino acids needed and digestion of certain plant proteins can be
insufficient to produce certain individual amino acids. In contrast, proteins
found in animal products are readily digestible and contain all essential amino
acids. Therefore, careful consideration should be given to the dietary intake of
individuals who may have or will be undergoing an increased level of exertion.
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