Chapter 23 Nitrogen Metabolism:

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Lecture 17 Chapter 23 Nitrogen
Metabolism Purines and Pyrimidines
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Purines 1. Start with ribose-5-P from the
pentose-phosphate pathway. 2. Build the purine
skeleton on that. inosine
ribose-5-P adenine
guanine

• Starts with ribose-5-P from the
• pentose phosphate pathway

ribose-5-P ribose-5-P
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(No Transcript)
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• 1. Inosine-5-phosphate is synthesized
• using, in part, 1C units requiring folic acid.
• Pregnant women need folic acid for
• nucleic acid synthesis.

3. Reactions involving tetrahydrofolate are
targets for chemotherapeutic agents.
methotrexate.
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4. Inosine monophosphate (IMP) is an
important intermediate in the synthesis of
both adenine guanine nucleotides.
5. Energy is required AMP equivalent of 8
ATP GMP equivlaent of 9 ATP Do you want to
make these nucleotices if you dont have to?
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6. The process is under feedback regulation.
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Catabolism of purine nucletodes

• RNA is degraded to AMP and GMP
• The phosphate is removed
• The base is degraded.

Or The Salvage pathway Base is reused. Why would
you want a salvage pathway?
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Pyrimidine Synthesis The bases are synthesized
first and then attached to the sugars.
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How are deoxyribonucleotides made?

• Ribonucleotide diphosphates are redicued
• to deoxyribonucleoside diphosphates.

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2. The conversion of uridine to thymidine.
Tetrahyhdrofolate
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• Take home lessons.
• Synthesizing purines and pyrimidines
• requires lots of energy. Therefore,
• a Regulation. Turn it off when you dont
• need it.
• b. Use the salvage pathway when you can.
• 1C units and tetrahydrofolate figure
• prominently.