Problem 1
Keto counterparts. Name the \(\alpha\) -ketoacid formed by the transamination of each of the following amino acids. (a) Alanine (d) Leucine (b) Aspartate (e) Phenylalanine (c) Glutamate (f) Tyrosine
Problem 2
A versatile building block. (a) Write a balanced equation for the conversion of aspartate into glucose through the intermediate oxaloacetate. Which coenzymes participate in this transformation? (b) Write a balanced equation for the conversion of aspartate into oxaloacetate through the intermediate fumarate.
Problem 4
Cooperation. How do aminotransferases and glutamate dehydrogenase cooperate in the metabolism of the amino group of amino acids?
Problem 5
Taking away the nitrogen. What amino acids yield citric acid cycle components and glycolysis intermediates when deaminated?
Problem 6
One reaction only. What amino acids can be deaminated directly? \(\ 1\)
Problem 7
Nitrogen sources. What are the immediate biochemical sources for the two nitrogen atoms in urea?
Problem 8
Counterparts. Match the biochemical on the right with the property on the left. (a) Formed from \(\mathrm{NH}_{4}^{+}\) (b) Hydrolyzed to yield urea (c) A second source of nitrogen (d) Reacts with aspartate (e) Cleavage yields fumarate (f) Accepts the first nitrogen (g) Final product 1\. Aspartate 2\. Urea 3\. Ornithine 4\. Carbamoyl phosphate 5\. Arginine 6\. Citrulline 7\. Argininosuccinate
Problem 10
A good bet. A friend bets you a bazillion dollars that you can't prove that the urea cycle is linked to the citric acid cycle and other metabolic pathways. Can you collect?
Problem 11
A precise diagnosis. The result of a reaction between an infant's urine and 2,4 -dinitrophenylhydrazine is positive. 2,4-Dinitrophenylhydrazine reacts with \(\alpha\) -ketoacids and suggests the presence of a high concentration of \(\alpha\) -ketoacids. Further analysis shows abnormally high blood levels of pyruvate, \(\alpha\) -ketoglutarate, and the \(\alpha\) -ketoacids of valine, isoleucine, and leucine. Identify a likely molecular defect, and propose a definitive test of your diagnosis.
Problem 13
Sweet hazard. Why should phenylketonurics avoid the ingestion of aspartame, an artificial sweetener? (Hint: Aspartame is L-aspartyl-L-phenylalanine methyl ester.)
