nitrogen balance

Question 1

how does nitrogen in the muscle get to the liver?

Answer 1

pyruvate gets converted to alanine in a transamination reaction utilising excess in the amino acids from the breakdown of muscle tissue.

Question 2

what is generated during transamination in the muscle?

Answer 2

alpha-ketoglutarate

goes into krebs

Question 3

what happens to alanine in the liver?

Answer 3

It gets converted back into pyruvate releasing its amine group converting alpha-ketoglutarate into glutamate (the reverse transamination reaction seen in the muscle)

Question 4

what happens to glutamate in the liver?

Answer 4

glutaminase removes an NH4+ group which can then enter the urea cycle

Question 5

what are the three substrates involved the urea cycle?

Answer 5

arginine, ornithine & citrulline

Question 6

what is arginine cleaved into? & what enzyme catalyses this?

Answer 6

• ornithine & urea

- arginase

Question 7

how is ornithine converted to citrulline?

Answer 7

addition of CO2 & ammonia

Question 8

how is citrulline converted to arginine?

Answer 8

addition of ammonia

Question 9

why is it essential ammonia is excreted and not allowed to build up in the blood?

Answer 9

• ammonia is neuro-toxic as it can pass through the blood brain barrier
• in the brain it causes alpha-ketoglutarate to be converted to glutamate causing the krebs cycle to stop
• patient is up shit creek with no paddle would most likely be confused if not in a coma