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NUCLEOTIDE BASES (DE NOVO (PYRIMIDINES: not initially attached to ribose 5…
NUCLEOTIDE BASES
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CATABOLISM:
- purines: uric acid -> excreted
- pyrimidines: Acetyl CoA, succinyl CoA (some energy gain)
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pyrimidines: NH4+, then to urea
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PURINE: A, G, I
PYRIMIDINE: C, U, T
liver, small intestine, thymus // CYTOSOL- main sites of prodxn
ATP used in GMP synthesis, GTP used in AMP synthesis
regulation: IMP levels, high = inhibit PRPP
NTP = precursor of dNTP, converted by ribonucleotide reductase (activated by ATP, inactivate by dATP)
AMINO ACIDS
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- PHASE 1:
- in the cytosol
- enzyme: AMINOTRANSFERASE
- most often transfer the removed NH3 to alpha ketoglutarate, produces Glu + ketoacid
then, oxidative deamination of glutamate:
glutamate + NAD(P)+ ---> alpha ketoglutarate + NADH
- enzyme: GLUTAMATE DEHYDROGENASE
- inhibited by GTP, activated by ADP
transdeamination of alanine:
- enzyme: ALANINE AMINOTRANSFERASE
- transfers the amino group from alalnine to alpha ketoglutarate to produce Glu
another important aminotransferase = aspartate aminotransferase, aspartate -> oxaloacetate
these two if [conc] too high in the blood, it's indicative of liver damage!!
B6: the aldehyde in it reacts w amines, to form pyridoxamine-P, which in turn donate the NH3 to alphaKG
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2 PHASES OF CATABOLISM:
PHASE 1:
- remove N (alpha amino) from aa
- strip off the NH3 = alpha ketoacid
(18/20aa undergo transdeamination)
(2/20 undergo deamination) - Lys, Thr
PHASE 2:
- metabolism of the alpha ketoacid
- so, the C-skeleton can enter metabolic pathways
(gluconeo, ketogenesis, CO2 + H2O)
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nitrogen balance: if intake = excretion
otherwise;
+ve N balance is where intake > excretion
-ve N balance is where excretion > intake
- PHASE 2:
- C-skeletons of degraded aa become one of the 7 metabolic intermediates:
1) acetyl CoA (ketogenic)
2) acetcacetyl CoA (ketogenic)
3) pyruvate
4) alphaKG
5) succinyl CoA
6) fumarate
7) oxaloacetate