3. 3
AMINO ACID UTILIZATION
The amino acid pool is the total supply
of free amino acids available for use in
the human body. Dietary protein is one
of three sources that contributes
amino acids to the amino acid pool.
The other two sources are protein
turnover and biosynthesis of amino
acids in the liver.
4. 4
AMINO ACID UTILIZATION
Protein turnover is the repetitive process
in which proteins are degraded and
resynthesized within the human body.
Nitrogen balance is the state that results
when the amount of nitrogen taken into
the human body as protein equals the
amount of nitrogen excreted from the body
in waste materials.
5. 5
AMINO ACID UTILIZATION
The amino acids from the body’s amino
acid pool are used in four different ways.
1.Protein synthesis.
2.Synthesis of nonprotein nitrogen-
containing compounds.
3.Synthesis of nonessential amino acids.
4.Production of energy.
8. 8
TRANSAMINATION AND OXIDATIVE DEAMINATION
A transamination reaction is a biochemical
reaction that involves the interchange of the
amino group of an a-amino acid with the
keto group of an a keto acid. The general
equation for a transamination reaction is
19. 19
TRANSAMINATION AND OXIDATIVE DEAMINATION
An oxidative deamination reaction is
a biochemical reaction in which an a-
amino acid is converted into an a-keto
acid with release of an ammonium ion.
Oxidative deamination occurs primarily
in liver and kidney mitochondria.
23. 23
THE UREA CYCLE
The urea cycle is the series of biochemical
reactions in which urea is produced from
ammonium ions and carbon dioxide. The
urea so produced is then transported in the
blood from the liver to the kidneys and
eliminated from the body in urine.
24. 24
THE UREA CYCLE
The urea cycle is the series of biochemical
reactions in which urea is produced from
ammonium ions and carbon dioxide. The
urea so produced is then transported in the
blood from the liver to the kidneys and
eliminated from the body in urine.
26. 26
THE UREA CYCLE
The “fuel” for the urea cycle is the
compound carbamoyl phosphate. This fuel
is formed from ammonium ion (from
oxidative deamination), carbon dioxide
(from the citric acid cycle), water, and two
ATP molecules. The formation equation for
carbamoyl phosphate is
34. 34
Steps of the Urea Cycle
Urea Cycle Net Reaction
The net reaction for urea formation, in
which all of the urea cycle intermediates
cancel out of the equation, is
35. 35
Steps of the Urea Cycle
Linkage Between the Urea and Citric
Acid Cycles
36. 36
AMINO ACID CARBON SKELETONS
A glucogenic amino acid is an
amino acid that has a carbon-
containing degradation product that
can be used to produce glucose
via gluconeogenesis.
37. 37
AMINO ACID CARBON SKELETONS
A ketogenic amino acid is an
amino acid that has a carbon-
containing degradation product
that can be used to produce
ketone bodies.
47. 47
Bile Pigments
The tetrapyrrole degradation products
obtained from heme are known as bile
pigments because they are secreted with
the bile, and most of them are highly
colored. A bile pigment is a colored
tetrapyrrole degradation product present in
bile.
48. 48
Biliverdin and bilirubin are,
respectively, green and reddish orange
in color. Stercobilin has a brownish
hue and is the compound that gives
feces their characteristic color. Urobilin
is the pigment that gives urine its
characteristic yellow color. Normally,
the body excretes 1–2 mg of bile
pigments in urine daily and 250–350
mg of bile pigments in feces daily.
49. 49
When the body is functioning properly, the
degradation of heme in the spleen to
bilirubin and the removal of bilirubin from
the blood by the liver balance each other.
Jaundice is the condition that occurs when
this balance is upset such that bilirubin
concentrations in the blood become higher
than normal. The skin and the white of the
eyes acquire a yellowish tint because of the
excess bilirubin in the blood.
50. 50
Jaundice can occur as a result of liver
diseases, such as infectious hepatitis
and cirrhosis, that decrease the liver’s
ability to process bilirubin; from spleen
malfunction, in which heme is
degraded more rapidly than it can be
absorbed by the liver; and from
gallbladder malfunction, usually from
an obstruction of the bile duct.
