The document discusses nucleic acid metabolism, focusing on nucleotide and nucleoside components, including their synthesis pathways, such as the de novo synthesis and salvage pathway for purines and pyrimidines. It highlights the importance of various enzymes in these processes and the roles of different tissues, particularly the liver and extrahepatic tissues, in metabolizing and salvaging nucleotides. Additionally, it outlines the biosynthesis and catabolism of purines and pyrimidines, as well as the regulation mechanisms for both types of nucleotides.

1. Nucleic Acid Metabolism
Mrs.R.Gloria Jemmi Christobel
Assistant Professor
Department of Biochemistry
V.V.Vanniaperumal College for Women,
Virudhunagar

2. Nucleotide & Nucleoside

3. • Nucleic acid consists of
Sugar (5 Carbon)
Nitrogenous base
Phosphate group
• Nitrogenous bases includes
PURINES
Adenine
Guanine
Pyrimidines
Cytosine
Thymine (DNA)
Uracil (RNA)

8. Purine Synthesis
• Two metabolic mechanism
• Denovo synthesis
• Salvage pathway
DENOVO SYNTHESIS
Activation of Ribose

10. • Enzymes:
(1) amidophosphoribosyltransferase;
(2) phosphoribosylglycinamide synthetase;
(3) phosphoribosylglycinamide formyltransferase;
(4) phosphoribosylformylglycinamidine synthetase;
(5) phosphoribosyl-aminoimidazole synthetase;
(6) phosphoribosylaminoimidazole carboxylase;
(7) phosphoribosylaminoimidazolesuccinocarboxamide
synthetase;
(8) adenylosuccinate lyase;
(9) phosphoribosylaminoimidazolecarboxamide
formyltransferase;
(10) IMP cyclohydrolase.

12. • De novo synthesis is particularly active in the
liver and placenta.
• Nonhepatic tissues (e.g., bone marrow)
depend on preformed purines that are
synthesized in the liver and transported by red
blood cells. They are very effective in salvaging
the purines and exhibit little or no xanthine
oxidase activity, which oxidizes free purines.

13. • Salvage Pathway
• The reutilization of purine bases, after conversion
to their respective nucleotides, constitutes
salvage pathways.
• These pathways are particularly important in
extrahepatic tissues.
• Purines arise from the intermediary metabolism
of nucleotides and the degradation
of polynucleotides.
• Salvage occurs mainly by the
phosphoribosyltransferase reaction: Human
tissue contains two phosphoribosyltransferases :

14. • Adenine phosphoribosyltransferase (APRT)
catalyzes the formation of AMP from adenine.
• Hypoxanthine guanine
phosphoribosyltransferase (HGPRT) catalyzes the
formation of IMP and GMP from hypoxanthine
and guanine, respectively.

16. Conversion of ribonucleotide to
deoxyribonucleotide

17. Catabolism of Purines

18. Pyrimidine Metabolism
• Biosynthesis of pyrimidine nucleotides can
occur by a de novo pathway or by the
reutilization of preformed pyrimidine bases or
ribonucleosides (salvage pathway)
• The biosynthesis of pyrimidine nucleotides
may be conveniently considered in two stages:
the formation of uridine monophosphate
(UMP) and the conversion of UMP to other
pyrimidine nucleotides.

22. Catabolism of Pyrimidines

23. Regulation of Purine Metabolism

24. Regulation of Pyrimidine Metabolism