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Biochemistry

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N Metabolism: Roles of Four Key Amino Acids

BIOCHM-DKH81I

Four amino acids, Ala, Asp, Gln, and Glu, play key roles in nitrogen metabolism in animals. The structures of these amino acids, but not their names, are shown below. All four of these amino acids are readily converted into citric acid cycle intermediates.

Grandjean, Nicolas. "Alanine aminotransferase." Wikimedia Commons. N.p., 2 Feb. 2006. Benzenamino. "Reaction Catalyzed by Aspartate Aminotransferase: Aspartate + α-ketoglutarate ⇌ Oxaloacetate + Glutamate." Wikimedia Commons. N.p., 16 May 2011. NEUROtiker. "L-Glutamine." Wikimedia Commons. N.p., 4 Feb. 2007. Web. 2 Sept. 2016. (Modified by M. Rumpho-Kennedy).

After identifying the four amino acids and considering their structures, identify ALL of the following statements which are NOT true relative to their role in N metabolism in humans.

Select ALL that apply.

A

In tissues other than the liver, potentially toxic excess ammonia can be detoxified by conversion to the amide nitrogen of Asp.

B

In muscle tissue, pyruvate is generated by glycolysis, and excess amino groups can be transferred to pyruvate forming the amino acid Ala. Ala moves through the bloodstream to the liver for further processing.

C

The most common route for amino group transfer in the liver is from amino acids to alpha-ketoglutarate forming Gln.

D

When Ala is deaminated in the liver, the C skeleton produced is pyruvate. Pyruvate can be converted back to glucose by gluconeogenesis and the glucose delivered to the muscles in the blood.

E

Asp is a key amino acid in the urea cycle providing one of the N in urea. Asp is generated by the transamination of oxaloacetate, a mitochondrial citric acid cycle intermediate.