All systems ↗Protein turnover supplies amino acids
Dietary absorption, protein breakdown, and new synthesis continually exchange amino acids; the body has no dedicated amino-acid storage depot.
CELLULAR ENERGY / 06
Amino acids split into nitrogen and carbon.
Amino acids primarily build proteins and specialized molecules. When they are exchanged or oxidized, cells must manage nitrogen safely while carbon skeletons connect with pyruvate, acetyl-CoA, and citric-acid-cycle intermediates.
Transamination redistributes nitrogen
Aminotransferases move amino groups between amino acids and keto acids. Glutamate is a central collector and donor.
Glutamine and alanine carry nitrogen
Tissues use these molecules to transport nitrogen and carbon between muscle, liver, kidney, gut, and other organs.
Urea enables excretion
Liver mitochondrial and cytosolic reactions convert much excess nitrogen to urea, which blood delivers to kidneys for urinary excretion.
Carbon enters shared junctions
Different amino acids yield pyruvate, acetyl-CoA, acetoacetate, alpha-ketoglutarate, succinyl-CoA, fumarate, or oxaloacetate.
Glucogenic carbon can support glucose
In liver or kidney, suitable carbon skeletons can contribute to gluconeogenesis during fasting or other demand states.
Ketogenic carbon yields acetyl units
Leucine and lysine are exclusively ketogenic; several other amino acids contribute both glucogenic and ketogenic carbon.
Branched chains begin in muscle
Skeletal muscle has substantial capacity for initial branched-chain amino-acid transamination; downstream products then move across tissues.