Question

MCAT Mini-Tutorial: Protein Metabolism

Answer 1

\({\bf{Ammonia:}}\) the body produces ammonia as a byproduct of respiration; excess ammonia in land dwelling animals must be excreted

- humans: production of urea in the liver which makes urine more concentrated
> amino acids transport ammonia to liver
> pyruvate (skeletal muscle) --> added to amino group via alanine aminotransferase (ALT) --> formation of alanine -->
> glutamate + amino group --> glutamine which is then discarded through oxidative deamination (trans-deamination)
> transaminases exchange amino groups between the amino acid and glutamate
> glutamate and glutamine donate their ammonia and form urea
> endergonic but coupled with the formation of fumarate which makes NADH

General Mechanism: 2 NH4+ + HCO3- + 3ATP + H2O --> urea + 2ADP + 4Pi + AMP + 2H+

> amino acids will either become glucose (gluconeogenesis) or ketones (acetyl coA)
> most amino acids become glucose
> leucine and lysine only become ketones

Answer 2

Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is the 2nd Edition Barron's Prep book for the new MCAT

(may add to this later)