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Practice
•
The principle mechanism for the removal
of amino groups for most amino acids
before their catabolism is:
(a) Oxidative deamination
(b) Transamination
(c) The action of a dehydratase enzyme
(d) The action of glutamine synthase
•
The principle mechanism for the removal
of amino groups for most amino acids
before their catabolism is:
(a) Oxidative deamination
(b) Transamination
(c) The action of a dehydratase enzyme
(d) The action of glutamine synthase
•
The primary nitrogenous excretion
product in human urine is:
(a) Ammonium ion
(b) Uric acid
(c) Creatinine
(d) Urea
•
The primary nitrogenous excretion
product in human urine is:
(a) Ammonium ion
(b) Uric acid
(c) Creatinine
(d) Urea
•
A compound common to the urea cycle
and the tricarboxylic acid cycle is
(a) Lactate
(b) Fumarate
(c) Pyruvate
(d) Alpha-ketoglutarate
•
A compound common to the urea cycle
and the tricarboxylic acid cycle is
(a) Lactate
(b) Fumarate
(c) Pyruvate
(d) Alpha-ketoglutarate
•
Which of the following amino acid has an
important role in the transport of amino
groups from peripheral tissues to the
liver?
(a) Serine
(b) Methionone
(c) Glutamine
(d) Arginine
•
Which of the following amino acid has an
important role in the transport of amino
groups from peripheral tissues to the
liver?
(a) Serine
(b) Methionone
(c) Glutamine
(d) Arginine
•
Which of the following amino acids is not
classified as glucogenic?
(a) Leucine
(b) Thryptophane
(c) Serine
(d) Aspartate
•
Which of the following amino acids is not
classified as glucogenic?
(a) Leucine
(b) Thryptophane
(c) Serine
(d) Aspartate
•
Which of the following amino acids is
required in the diet of a healthy adult?
(a) Aspartate
(b) Serine
(c) Thryptophan
(d) Glutamine
•
Which of the following amino acids is
required in the diet of a healthy adult?
(a) Aspartate
(b) Serine
(c) Thryptophan
(d) Glutamine
Ammonia Toxicity Resulting from an Arginine-Deficient
Diet
In a study, cats were fasted overnight than given a single meal complete in all
amino acids except arginine. Within 2 hours, blood ammonia levels
increased from a normal level 18 mg/L to 140 mg/L, and the cats showed
the clinical symptoms of ammonia toxicity. A control group fed a complete
amino acid diet or an amino acid diet in which arginine was replaced by
ornithine showed no unusual clinical symptoms.
a)
What was the role of fasting in the experiment?
b)
What caused the ammonia levels to rise in the experimental group? Why
did the absence of arginine lead to ammonia toxicity? Is the arginine an
essential amino acid in cats? Why or why not?
c) Why can ornithine be substituted for arginine?
Transamination and Urea Cycle
Aspartate aminotransferase (AST) has the highest
activity of all the mammalian liver aminotransferases.
Why?
Lactate versus Alanine as Metabolic Fuel: The
Cost of Nitrogen Removal.
The three carbons in lactate and alanine have identical
oxidative state and animals can use either carbon source
as a metabolic fuel. Compare the ATP yield (moles of
ATP per mole of substrate) for the complete oxidation (to
CO2 and H2O) of lactate versus alanine when the cost of
nitrogen excretion as urea is included.
A Genetic Defect in Amino Acid Metabolism: A
Case History.
A two-years-old child was vomited frequently, especially after
feeding. The child’s weight and physical development were
below normal. His hair, although dark, contained patches of
white. A urine sample treated with ferric chloride (FeCl2) gave a
green color characteristic of the presence of phenylpyruvate.
Quantitative analysis of urine gave the results shown in the
table.
Substance
Concentration (mM)
Patient’s urine
Normal urine
Phenylalanine
7.0
0.01
Phenylpyruvate
4.8
0
10.3
0
Phenyllaktate
a)
Suggest which enzyme might be deficient in this child. Propose a
treatment
b)
Why does phenylalanine appear in the urine in large amount.
c)
Why is the source of phenylpyruvate and phenyllactate? Why
does this pathway (normally not functional) come into play when
the concentration of phenylalanine is rises?
d)
Why does the boy’s hair contain patches of white?
Biosynthesis of tyrosine from phenylalanine
Phenylalanine hydroxylase is a mixed-function oxygenase: one atom of oxygen is
incorporated into water and the other into the hydroxyl of tyrosine. The reductant is the
tetrahydrofolate-related cofactor tetrahydrobiopterin, which is maintained in the reduced
state by the NADH-dependent enzyme dihydropteridine reductase
Phenylketonuria
• Hyperphenylalaninemia - complete
deficiency of phenylalanine hydroxylase (plasma
level of Phe raises from normal 0.5 to 2 mg/dL to
more than 20 mg/dL).
• The mental retardation is caused by the
accumulation of phenylalanine, which becomes a
major donor of amino groups in
aminotransferase activity and depletes neural
tissue of α-ketoglutarate.
• Absence of α-ketoglutarate in the brain shuts
down the TCA cycle and the associated
production of aerobic energy, which is essential
to normal brain development.
• Newborns are routinelly tested for blood
concentration of Phe.
• The diet with low-phenylalanine diet.
Melanin synthesis
Alanine and Glutamine in the Blood.
Normal human blood plasma contains all the amino acids require for
the synthesis of body proteins, but not in equal concentration.
Alanine and glutamine are present in much higher concentrations
than other amino acids. Suggest why?
Answer :
Muscle tissue can convert amino acids to their keto acids plus
ammonia, than oxidize the keto acids to produce ATP from muscle
contraction. However, urea cannot be formed in muscle. Alanine and
glutamine transport amino group in the bloodstream to the liver from
muscle and other nonhepatic tissues.
• Compartmentation in β-oxidation
Free palmitate is activated to its coenzyme A derivative ( palmitoyl-CoA) in
cytosol before it can be oxidized in the mitochondrion. If palmitate and
14C coenzyme A are added to a liver homogenate, palmitoyl-CoA isolated
from the cytosolic fraction is radioactvive, but that isolated from the
mitochondrial fraction is not.
Explain.
• Mutant Carnitine palmitoyltransferase I
• What changes in metabolic pattern would result from a mutation in
the muscle carnitine palmitoyltransferase I in which the mutant
protein has lost its affinity for malonyl-CoA but not its catalytic
activity?
• FA oxidation in Uncontrolled Diabetes
• When the acetyl-CoA produced during β – oxidation in the liver
exceeds the capacity of the citric acid cycle, the excess acetyl-CoA
forms ketone bodies. This occurs in severe, uncontrolled diabetes:
because the tissue cannot use glucose, they oxidize large amounts
of FA instead. Although acetyl-CoA is not toxic, the mitochondrion
must divert the acetyl-CoA to ketone bodies.
• What problem would arise if acetyl-CoA were not converted to
ketone bodies?
• Consequences of a High-Fat Diet with No
Carbohydrate.
• What would be effect of carbohydrate deprivation on the utilization of
fats for energy?
• If your diet were totally devoid of carbohydrate, would it be better
to consume odd- or even- numbered FA?
• Explain
• Effect of PDE Inhibitor on Adipocytes
• How would an adipocyte´s response to epinephrine or glucagon be
affected by addition of an inhibitorof cAMP phosphodiesterase
(PDE)