Covers the structure of purines and how purine nucleotides are built, both by the de novo route in the cytoplasm and by the salvage route, with the key enzymes named for each. It then describes degradation to uric acid via xanthine oxidase, the regulatory enzymes and their feedback inhibitors, and purine analogues used as antiviral agents. The note closes with hyperuricaemia and gout, Lesch-Nyhan syndrome, xanthine oxidase inhibitors such as allopurinol, and a short set of multiple-choice questions with answers.
Topic 39 of 70 in the MU Sofia syllabus for Biochemistry (Medicine, Year 2). The free AceMed note covers it in 11 sections, about 569 words (4 min of reading), with 10 flashcards.
In this note
INTRODUCTION
BIOSYNTHESIS AND DEGRADATION OF PURINE NUCLEOTIDES:
De novo synthesis of purine nucleotides
Salvage pathway for purine nucleotides
REGULATORY ENZYMES IN BIOSYNTHESIS:
PURINE ANALOGS AS ANTIVIRAL AGENTS:
HYPERURICEMIA DUE TO ENZYME DEFECTS:
LESCH-NYHAN SYNDROME:
INHIBITION OF XANTHINE OXIDASE:
MCQS☺
ANSWERS
INTRODUCTION
Purines are organic compounds that are integral to the structure and function of genetic material (DNA and RNA) and play critical roles in cellular processes. They are composed of a double-ring structure, with one ring being a pyrimidine and the other an imidazole. Adenine and guanine are the two primary purines found in nucleic acids. These molecules are essential for storing and transferring energy within cells, serving as components of important cellular messengers like ATP and GTP, and participating in metabolic pathways.
BIOSYNTHESIS AND DEGRADATION OF PURINE NUCLEOTIDES:
Biosynthesis:
Purine nucleotides are essential building blocks for DNA and RNA synthesis.
Biosynthesis occurs through the de novo and salvage pathways.
De novo synthesis: Occurs in the cytoplasm and involves the step-by-step assembly of purine nucleotides from simple precursors.
Salvage pathway: Utilizes preformed purine bases (hypoxanthine, guanine) salvaged from the degradation of nucleic acids or dietary sources.
Key enzymes involved in de novo synthesis include amidophosphoribosyltransferase (PRPP amidotransferase), phosphoribosylglycinamide synthetase, phosphoribosylformylglycinamidine synthase, and others.
Salvage pathway enzymes include hypoxanthine-guanine phosphoribosyltransferase (HGPRT) and adenine phosphoribosyltransferase (APRT).
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