AMINO ACIDS
Amino Acids are the building
blocks of Proteins
• Composed of C, H, O, N usually S, P
• Always has a NH2
General Structure
• All amino acids start
with this structure
• The “R” stands for
“anything”
Glycine
• Glycine has just a
hydrogen for the “R”
• NOT essential,
except for the baby
chick
Alanine
• Alanine has a
methyl group for the
“R”
• Has 3 carbons
(glycine had just 2)
• NOT essential
Serine
• NOT essential
Threonine
• Essential
Valine
• Essential
• Valine is a branched
chain amino acid.
• An "ideal protein"
would contain 70%
as much isoleucine
as lysine.
• A rare, inherited metabolic disease in
which there is a failure of oxidative
decarboxylation (breakdown) of valine,
leucine and isoleucine results in maple
syrup urine disease, named because of
a characteristic odor of the urine.
Leucine
• Leucine is abundant in corn protein and
many other grain proteins, and is not
therefore a concern to supplement. Only
the L isomer has biological value. "Ideal
protein" would contain 100% as much
leucine as lysine.
Isoleucine
• Isoleucine is a branched chain amino
acid. An "ideal protein" would contain
one-half as much isoleucine as lysine.
• A rare, inherited metabolic disease in
which there is a failure of oxidative
decarboxylation (breakdown) of valine,
leucine and isoleucine results in maple
syrup urine disease, named because of
a characteristic odor of the urine.
Phenylalanine
• Phenylalanine is not tolerated by people
with inborn errors of PHE metabolism
so they must avoid it. Babies are given
a PKU (phenylketonuria) test at birth to
detect phenylalanine metabolites in the
urine, so they can be treated in order to
avoid a dangerous condition.
• PHE is combined with ASP (aspartic
acid, another amino acid) in the
common non-nutritive sweetner
aspertame. Equal is another trade
name.
Methionine
• Methionine is a
sulfur-containing
amino acid.
• A portion of the
methionine
requirement can be
met from cystine,
another sulfurcontaining amino
acid.
• An "ideal protein" would contain onehalf as much methionine + cystine as
lysine.
• Unlike most amino acids, both the d and
l isomers of methionine are biologically
active. Consequently, it has been
synthesized and can be economically
purchased for adding to diets.
• Methionine participates in acting as a
methyl donor, and is involved in the
synthesis of many important
compounds in the body, including
epinephrine and choline.
Cysteine
Cystine
Tryptophan
• Tryptophan is the
second most limiting
amino acid in corn
diets for pigs.
• Tryptophan can be used to from the
Vitamin niacin but since feeds are
usually low in tryptophan and the
synthesis is insufficient to meet daily
needs, it is not relied upon to meet the
animal's need.
• Useful in aiding sleep, tryptophan
supplements have been banned by FDA
as dangerous.
• Skatole and indole can be formed from
its breakdown in the large intestine by
bacteria, producing foul odors.
Arginine
• Arginine is a precursor of
urea in the body. Urea is the
form in which nitrogen is
removed from mammals, so
normal breakdown of protein
and deamination of amino
acids will result in urea
formation, requiring arginine.
Histidine
• Histidine contains
an imidazole group.
It is a precursor of
histamine. An "ideal
protein" would
contain 33% as
much histidine as
lysine.
Lysine
• Lysine is the most limiting amino acid in
corn and most grains for swine and poultry.
• Diets balanced for lysine will contain
most of the other amino acids in excess
of requirement if natural sources of
good quality proteins are used.
• It can be supplemented in the synthetic
form and this is often economical,
replacing a portion of the protein
needed.
• Only the L isomer is biologically active.
Essential Amino Acids
Clue to remember: PVT TIM HALL
•
•
•
•
•
Phenylalanine
Valine
Threonine
Tryptophan
Isoleucine
•
•
•
•
•
Methionine
Histidine
Arginine
Lysine
Leucine
How do the amino acids differ
from what is in DNA?
• DNA is composed of
nucleic acids
(purines and
pyrimidines)
• Purines
– adenine, guanine
• Pyrimidines
– cytosine, thymine
• Adenine
Guanine
PURINES
Cytosine
Thymine
PYRIMIDINES