Title: Nucleic Acid Metabolism
1Nucleic Acid Metabolism
- Nucleotides
- Essential for all cells
- Carriers of activated intermediates in
carbohydrate, lipids and proteins - CoA
- FAD
- NAD
- NADP
- Energy Carriers
- ATP
- Inhibiting or activating enzymes
- DNA
- RNA
2Nucleotide Structure
- Ribose Sugar
- Ribose
- Deoxyribose
- Base
- Purines
- Pyrimidines
- Nucleoside
- Base plus sugar
- Nucleotide
- E.g., AMP, ADP, ATP
3Nomenclature
- DNA Purine Bases
- Adenine
- Guanine
- Purine Nucleosides
- Adenosine
- Guanosine
- DNA Nucleotides (Purine)
- dAMP (deoxyadenylate)
- dGMP (deoxyguanylate)
- RNA Nucleotides (Purine)
- Adenylate (AMP)
- Guanylate (GMP)
4Nomenclature Continued
- DNA Pyrimidine Bases
- Thymine
- Cytosine (Also RNA)
- DNA Pyrimidine Nucelosides
- Thymidine
- Cytidine
- DNA Pyrimidine Nucleotides
- (dTMP) deoxythymidylate
- (dCMP) deoxycytidylate
- RNA Pyrimidine Nucleotides
- (CMP) cytidylate
- (UMP) uridylate
5PRPP 5-Phosphoribosyl 1-Pyrophosphate
- Addition of the ribose sugar component
- HMP
- ATP Required
- Mg
- Pi activates and nucleosides inhibit
6Pyrimidine Synthesis
- UMP (Uridine 5-monophosphate) to UTP
- Precursor to CTP
- Occurs on mitochondria inner membrane
- Carbamoyl phosphate synthetase II
- Different from CPS I
- CPS I uses free ammonia
- CPS II uses glutamine for amino source
7Carbamoyl Phosphate Synthetase II
8Formation of Uridine 5-phosphate
9Enzymes of Pyrimidine Biosynthesis
10UTP to CTP Conversion
11Conversion of Ribonucleotides to
Deoxyribonucleotides
- Ribonucleotide reductase
- NADP
- Thioredoxin reductase
- Example is production of dCDP
12Allosteric Inhibition of Ribonucleotide Reductase
- ATP activates
- dATP inhibits
13Thymidylate Biosynthesis
- Substrates and Vitamins
- dUMP
- Folate (N5, N10,-Methylene-THF)
- Glycine/Serine
- NADP
14Conversion of dUMP to dTMPOverall
- 5-fluorouracil
- Methotrexate
15Thymidylate PathwaySpecific
16Thymidylate Synthesis and Cancer Chemotherapy
- Thymidylate synthase is target for fluorouracil
- Action is 5-fluorouracil (5-FU)is converted to
5-fluoro-2-deoxyuridylate (dUMP structural
analog) - Then 5-fluoro-2-deoxyuridylate binds to the
enzyme Thymidylate Synthase and undergoes a
partial reaction where part of the way through
5-fluoro-2-deoxyuridylate forms a covalent
bridge between Thymidylate Synthase and N5,
N10-Methylene THF and is an irreversible
inhibition. - Normally, the enzyme, Thymidylate Synthase and
the vitamin would NOT be linked together
permanently - This type of inhibition is called suicide-based
enzyme inhibition because the inhibitor
participates in the reaction causing the enzyme
to react with the compound producing a compound
that inactivates the enzyme itself.
17Fluorouracil Pathway
Suicide inhibition because Flurouracil does not
directly inhibit enzyme.
18Methotrexate
- Competitive inhibitor of Dihydrofolate Reductase
- Used in,
- Acute lymphoblastic leukemia
- Osteosarcoma in children
- Solid tumor treatment
- Breast, head, neck, ovary, and bladder
- Prevents regeneration of tetrahydrofolate and
removes activity of the active forms of folate
19Leucovorin Rescue Strategy in Methotrexate
Chemotherapy
- Patients given sufficient methotrexate that if
were not followed by Leucovorin (N5-methenyl-THF)
would be fatal. - All neoplastic cells are killed
- Patients are rescued (6-36 hours) by the
Leucovorin (Folate) otherwise would die due to
permanent tetrahydrofolate shutdown. - Tumor resistance to methotrexate can occur in
patients who have gene amplification of
dihydrofolate reductase (in tumor cells) - More dihydrofolate reductase is produced by more
than the normal active genes usually present in
normal cells.
20Purine Biosynthesis
- IMP (Inosine Monophosphate)
- Precursor to
- GMP and AMP
- Utilizes (Substrates)
- Glycine
- Glutamine
- ATP
- Folate (N10-formyl-THF)
- Aspartate
- CO2
- PRPP amidotransferase is rate limiting
- Inhibited by AMP and GMP
21IMP Pathway
22IMP to AMP and GMP
- Glutamine, NAD, ATP used in GMP production
- Aspartate, GTP used AMP production
23AMP and GMP Pathway
24Nucleotide Pyrimidine Catabolism
- Degradation of pyrimidine metabolites
- UMP, CMP, TMP
- End products are acetyl-CoA and Propionyl-CoA
- Ribose sugar component may be converted to
ribose-5-phosphate which is a substrate for PRPP
Synthetase - Ribose sugar component may be further catabolized
in HMP pathway
25Pyrimidine Catabolic Pathway
26Purine Catabolism
27Regulation of Nucleotide Metabolism
- Pyrimidine Regulation
- Primary regulatory step is Carbamoyl Phosphate
via Carbamoyl Phosphate Synthetase II - Purine Regulation
28Action of Allopurinol
- Allopurinol is purine
- base analog
- Three mechanisms
- Allopurinol is oxidized to alloxanthine by
xanthine dehydrogenase - Then Allopurinol and alloxanthine are inhibitors
of xanthine dehydrogenase - This inhibition decreases urate formation
- Then concentrations of Allopurinol and
alloxanthine increase but do not precipitate as
urate does. - Allopurinol and alloxanthine are excreted into
the urine
29Action of AllopurinolPathway
30Biosythesis of Nucleotide Coenzymes
- CoA
- OTC is pantothenate
- Uses ATP, CTP, Cysteine
31Coenzyme A Pathway
32FMN and FAD
- OTC is riboflavin
- Consumes ATP