Chapter 25: Protein and Amino acid metabolism

Turnover

is the continual renewal or replacement of biomolecules; for protein it is defined by the balance between protein synthesis and protein degradation.

Transamination

is the interchange of the amino group of an amino acid and the keto group of an alpha- keto acid.

Oxidative deamination

is the conversion of an amino acid ¬NH2 group to an alpha- keto group, with removal of NH4 +.

Human bodies

do not store nitrogen- containing compounds, and ammonia is toxic to cells.

Reductive amination

: conversion of an alpha- keto acid to an amino acid by reaction with NH4 +.

Mammals

must first convert ammonia, in solution as ammonium ion, to nontoxic urea via the urea cycle.

Incorporation of the carbon

atoms into compounds that can enter the citric acid cycle.

Amino acid pool

is the entire collection of free amino acids in the body.

alpha ketoglutarate

The is converted to glutamate, and the amino acid is converted to an alpha- keto acid.

Transamination is the interchange of the amino group of an amino acid and the keto group of an alpha

keto acid

STEPS 1 AND 2 OF THE UREA CYCLE

Building Up a Reactive Intermediate The first step of the urea cycle transfers the carbamoyl group, H2NC=O, from carbamoyl phosphate to ornithine, an amino acid not found in proteins, to give citrulline, another non-protein amino acid

Nonessential amino acid

one of 11 amino acids that are synthesized in the body and are therefore not necessary in the diet

Essential amino acid

an amino acid that cannot be synthesized by the body and thus must be obtained from the diet

Reductive amination

conversion of an alpha-keto acid to an amino acid by reaction with NH4 +

amino acid pool

the entire collection of free amino acids in the body.

ketogenic amino acids

Those amino acids that are converted to acetoacetyl-CoA or acetyl-CoA then enter the ketogenesis pathway and are called ketogenic amino acids.

reductive amination

conversion of an alpha-keto acid to an amino acid by reaction with NH4 +.