Question

Explain how amino acids can be used a source of energy, and outline how ammonia is detoxified.

Answer 1

Amino acids are broken down to form energy generating compounds.Glucogenic amino acids like alanine, serine, glycine are converted into glucose,which is then used as energy source by the body.Another way of using amino acids as energy source involves Krebs cycle.When level of glucose is low in body,amino acids are converted to 4-5 carbon molecule ,which then enters Krebs cycle to generate glucose.

Detoxification of ammonia in body

At cellular level ammonia exists in form of ammonium ions.If ammonium ion concentration rise in body comma may result( hepatic coma).There are two mechanisms to detoxify ammonia in body.

1.Glucose alanine cycle-In glucose alanine cycle ammonium ions are transported from muscles to liver to form alanine.In liver alanine is transaminated to form pyruvate which can be used in gluconeogenesis.

2.Second mechanism is glutamine synthase mechanism.Enzyme glutamine synthase catalyses following reaction.

Glutamate+ammonia+ATP------->gltamine+ADP+(P)

Ammonia is converted to amino acid glutamine.Glutamine further carries ammonia from peripheral tissues to liver and kidneys.In liver and kidneys ammonia is released by glutaminase to form H4+ ions.In liver released ammonia is used for synthesis of urea while in kidneys it is excreted in urine.