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 CycleAspartate 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

Phenyllaktate 10.3 0

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

• 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.

Phenylketonuria

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)