Amino-acid catabolism, urea cycle, de-novo purine/pyrimidine biosynthesis, one-carbon metabolism.
Amino Acid And Nucleotide Metabolism
Transamination
α-Amino group transfer from amino acid to α-ketoglutarate (→ glutamate) by aminotransferases using pyridoxal-phosphate cofactor. Central to…
Urea cycle
Five-step hepatic cycle converting toxic ammonia + aspartate → urea (ureotelic nitrogen excretion). Split between mitochondria (CPS1, OTC)…
De-novo purine biosynthesis
Ten-step assembly of IMP on PRPP scaffold, incorporating Gly, Gln, Asp, and formyl-THF. IMP branches to AMP (via adenylosuccinate) and GMP…
De-novo pyrimidine biosynthesis
Six-step biosynthesis of UMP from carbamoyl-P + aspartate (via CAD complex + DHODH + UMPS). UMP → UTP → CTP; dUMP → dTMP by thymidylate…
Nucleotide salvage
Recycling free bases/nucleosides to nucleotides via HGPRT, APRT, TK, DCK, adenosine kinase. HGPRT deficiency → Lesch-Nyhan syndrome.
Folate one-carbon metabolism
Tetrahydrofolate (THF) carries one-carbon units (methyl, methylene, formyl) for thymidylate, purine, and methionine synthesis. Vitamin-B9…
Ketogenic vs glucogenic amino acids
Degradation products enter either ketone-body pathway (Leu, Lys — pure ketogenic) or gluconeogenesis (Ala, Gly, Ser — pure glucogenic).…
Essential amino acids
Nine amino acids humans cannot synthesise: His, Ile, Leu, Lys, Met, Phe, Thr, Trp, Val. Must be obtained from diet. Limiting amino acid in…
Purine salvage (HGPRT)
Hypoxanthine-guanine phosphoribosyltransferase recycles purine bases to nucleotides. Deficiency → Lesch-Nyhan syndrome (hyperuricemia,…
Ammonia detoxification
Hepatic urea cycle (humans); glutamine synthesis (brain, muscle); uric acid excretion (birds, reptiles). Hyperammonemia → hepatic…