Chapter18Fall2005 - Copy

Chapter18Fall2005 - Copy - Chapter 18 Nucleotide Metabolism...

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Roles of nucleotides in the cell: 1) Activated precursors of DNA and RNA 2) Nucleotide derivatives are activated intermediates in many biosynthetic pathways e.g. UDP-glucose, CDP-diacylglycerol 3) Universal currency of cell (i.e. ATP) 4) Components of three major coenzymes: NAD + , FAD, and CoA 5) Metabolic regulators (i.e. cyclic AMP) Nucleotide synthesis can either by de novo or by recycling preformed bases (salvage pathway). Nomenclature : Nucleotides are composed of three components: 1) nitrogenous base - pyrimidine (cytosine, uracil, thymine) or purine (adenine or guanine) 2) pentose sugar - ribose (RNA) or deoxyribose (DNA) 3) phosphate group nucleoside - purine or pyrimidine base linked to pentose sugar nucleotide - phosphate ester of nucleoside SYNTHESIS OF PURINE NUCLEOTIDES Purine ring is synthesized de novo from 5 different precursors: aspartate (N-1 atom), CO 2 (C-6 atom), glycine (C-4, C-5, N-7 atoms), tetrahydrofolate (C-2, C-8 atoms) and glutamine ( N-3, N-9). Purine ring structure is synthesized from ribose 5-phosphate; PRPP then donates ribose 5- phosphate for purine synthesis. Purine ring is built onto the ribose 5-phosphate via a 10 -tep pathway: glutamine, glycine, tetrahydrofolate, and glutamine make contributions to form 5-membered ring; construction of 6-membered ring forms inosine 5’-monophosphate (IMP). IMP can be converted into AMP or GMP For AMP synthesis, aspartate amino group condenses with keto-group of IMP; GTP- dependent reaction For GMP synthesis, C-2 is oxidized to form xanthosine monophosphate (XMP) Amide nitrogen of glutamine replaces oxygen of C-2 to form GMP ATP-dependent reaction Synthesis of purine bases using the salvage pathway: Free purine bases are formed by degradation of nucleic acids and nucleotides. 1
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This note was uploaded on 08/02/2009 for the course BIOCHEMIST 100 taught by Professor Crew during the Spring '05 term at North Alabama.

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Chapter18Fall2005 - Copy - Chapter 18 Nucleotide Metabolism...

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