nucleotide metabolism siti annisa devi trusda. nucleotides are essential for all cells dna/rna...
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NUCLEOTIDE METABOLISMSITI ANNISA DEVI TRUSDA
Nucleotides are essential for all cellsDNA/RNA synthesisprotein
synthesiscells proliferateCarriers of activated intermediates in the
synthesis of carbohydrate, lipids and protein
Structural component of several essential coenzymes (coA,FAD,NAD+,NADP+)
cAMP,cGMP2nd messenger in signal transduction pathway
Important regulatory compound for many of the pathways of intermediary metabolism, inhibiting/activating key enzimes
Nucleotide structureConsist of:
◦Nitrogenous base : purine & pyrimidine◦Pentose monosaccharide◦1/2/3 phosphate groupsDNA and RNA contain the same purine
bases: A & GPirimidine RNA : U & C DNA : T & CT& U differ by only one methyl group
NucleosidesPentose sugar + Nitrogen Base =
NucleosidesSo, nucleotides = Nucleosides +
PhosphateIf the sugar is ribose : ribonucleosidesIf deoxyribose: deoxyribonucleosidesRibonucleosides of A,G,C,U:
Adenosine,Guanosine,Cytidine,UridineWhat are the deoxyribonucleosides
for A,G,C,T?
Nucleotides
mono,di,tri esters of nucleosides1st phosphate group is attached by an
ester linkage to the 5’OH of the pentosenucleoside 5’phosphate/5’-nucleoside
Type of pentose is added as prefix for nucleotide, can be ribose/deoxyribose e.g: 5’-ribonucleotide/5’-deoxyribonucleotide
1 phosphate group + 5’-carbon of the pentosenucleoside monophosphate(NMP) e.g AMP, CMP
2 or 3 phosphate group added to the nucleosidenucleoside di/triphosphate e.g ADP/ATP
The latter connected to the nucleotide by a high-energy bond
Phosphate groups(-) charge DNA/RNA=nucleic acids
So, what is :◦Nucleoside?◦Nucleotide?◦Nucleic acid?
SYNTHESIS OF PURINE NUCLEOTIDESSource of purine ring: aspartic acid,
glycine, glutamine, CO2,N10-formylTHFSynthesis of 5-phosphoribosyl-1-
pyrophosphate (PRPP)an activated pentose for synthesis of
purine/pirimidine & salvage of purine basescatalyzed by PRPP synthetase, from ATP &
ribose 5-phosphatethis enzyme is activated by inorganic
phosphat (Pi), inhibited by purine nucleotidesthe sugar of PRPP is ribose ribonucleotides
as end product of purine synthetis
Purine synthesis is critical to fetal development, therefore defects in enzymes will result in a nonviable fetus.
PRPP synthetase defects are known and have severe consequences (next slide)
PRPP synthetase superactivity has been documented, resulting in increased PRPP, elevated levels of nucleotides, and increased excretion of uric acid.
Phosphoribosyl Pyrophosphate (PRPP) Synthetase Defects
PRPP deficiency results in convulsions, autistic behavior, anemia, and severe mental retardation.
Excessive PRPP activity causes gout (deposition of uric acid crystals), along with various neurological symptoms, such as deafness.
Synthesis of 5’-phosphoribosylamine
Amide group of glutamine replaces the pyrophosphate group at C1 of PRPP
the enzyme, glutamine:phosphoribosyl pyrophosphate amidotransferase is inhibited by the purine 5’-nucleotides AMP,GMP,IMP (end product)
Committed stepRate of reaction also controlled by
intracellular [] of glutamine and PRPP
Synthesis of inosine monophosphate,the “parent” of purine nucleotide
requires 4 ATP2 steps require N10 –
formyltetrahydrofolate
Conversion of IMP to AMP and GMP
2 step energy requiring pathwaysynthesis of AMP requires GTP as
energy sourcesynthesis of GMP requires ATP
Conversion of nucleoside monophosphates to nucleoside di and triphosphate
AMP + ATP ↔ 2 ADP
GMP +ATP ↔ GDP + ADP
GDP + ATP ↔ GTP + ADP
CDP + ATP ↔ CTP + ADP
Purine Synthesis
DAUR dr IMP AMP & GMP
IMP dehidrogenase
XMP aminase
Adenilosuksinat synthetase
Adenilosuksinat lyase
Salvage Pathway of purines
Purines that result from the normal turnover of cellular nucleic acids/diet can be reconverted into nucleoside triphosphatessalvage pathway
2 enzymes: Adenine phosphoribosyltransferase (APRT), and hypoxanthine-guanine phosphoribosyltransferase (HPRT)
Both needs PRPP as the source of the ribose 5-phosphate
Degradation of Purine Nucleotides Purine Nucleotides from ingested
nucleic acids or turnover of cellular nucleic acids is excreted by humans as uric acid.
Humans excrete about 0.6 g uric acid every 24 hours.
Degradation of dietary nucleic acids occurs in the small intestine by pancreatic enzymes
Digestion of dietary nucleic acids
In the stomach: low pH denatures DNA&RNA
In small intestine: break down phosphodiester bond by endonuclease (pancreas) oligonucleotide
By phosphodiesterase(exonuclease non spesific enzyme) mononucleotide
By phosphomonoesterase (nucleotidase) result: nucleoside and orthophosphate.
Nucleosida phosphorylase result: base and ribose-1-phosphate.
The nucleoside then absorbed by intestinal mucosal cells
If the base or nucleoside is unused, it will be reused in salvage pathways, the base will be degraded:
uric acid ureidopropionic
(purin) (pyrimidine).
Diseases associated with purine degradation
GoutElevated uric acid levels
in the bloodUric acid crystals will
form in the extremities with a surrounding area of inflammation. This is called a tophus and is often described as an arthritic “great toe”.
Can be caused by a defect in an enzyme of purine metabolism or by reduced secretion of uric acid into the urinary tract.
tophus
Adenosine Deaminase (ADA) and Purine Nucleoside Phosphorylase (PNP) Deficiency.
accumulation of adenosine wich is converted to its ribonucleotide or deoxyribonucleotide form by cellular kinases
As dATP level rise, ribonucleotide reductase is inhibited↓ production of all deoxyribose containing nucleotidescells cannot make DNA and divide.
Most severe form: severe combined immunodeficiency disease (SCID)lack of T and B cells
A deficiency of either ADA or PNP causes a moderate to complete lack of immune function.
Affected children cannot survive outside a sterile environment.
They may also have moderate neurological problems, including partial paralysis of the limbs.
When a compatible donor can be found, bone marrow transplant is an effective treatment.
Lesch-Nyhan SyndromeHypoxanthine Guanine
Phosphoribosyltransferase (HGPRT) deficiency
X-linked genetic conditionSevere neurologic disease, characterized
by self-mutilating behaviors such as lip and finger biting and/or head banging
Up to 20 times the uric acid in the urine than in normal individuals. Uric acid crystals form in the urine.
Untreated condition results in death within the first year due to kidney failure.
Treated with allopurinol, a competitive inhibitor of xanthine oxidase.
SYNTHESIS OF DEOXYRIBONUCLEOTIDES
Deoxyribonucleotides required for DNA synthesis (2’-deoxyribonucleotides)
Enzyme: ribonucleotide reductase Inhibitor : dATPNeeded a coenzyme : thioredoxinThioredoxin is regenerated by
thioredoxin reductase Regulation of ribonucleotide reduction
is controlled by allosteric feedback mechanisms.
PYRIMIDINE SYNTHESIS AND DEGRADATION
Source of pyrimidine ring: glutamine, CO2, aspartic acid
Synthesis of carbamoyl phosphate
from glutamine & CO2, enzyme: carbamoyl phosphate synthetase II (CPS II), inhibited by UTP
activated by ATP and PRPP
Synthesis of orotic acidformation of
carbamoylaspartatedihydroorotateorotic acid (mind the enzymes!!)
Formation of a pyrimidine nucleotide : orotidine 5’-monophosphate (OMP)the parent of pyrimidine mononucleotide
OMPUridine monophosphate (UMP)Synthesis of uridine triphosphate
and cytidine triphosphateCTP is produced by amination of UTPSynthesis of thymidine
monophosphate from dUMP
Orotat fosforibosiltransferase
Orotidilate dekarboksilase
UMP kinase
CTP synthetase
Nukleosida diphosphat kinase
Pyrimidine Synthesis
Production of Uridine 5’-
monophosphate (UMP) from orotate is
catalyzed by the enzyme UMP
synthase
Orotic AciduriaDeficiency in UMP synthetase activityDue to the demand for nucleotides in the
process of red blood cell synthesis, patients develop the condition of megaloblastic anemia, a deficiency of red blood cells.
Pyrimidine synthesis is decreased and excess orotic acid is excreted in the urine (hence the name orotic aciduria)
Degradation of pyrimidine nucleotides
Unlike the purine rings, which are not cleaved in human cells, the pyrimidine ring can be opened and degraded to highly soluble structures, such as β-alanine, and β-aminoisobutyrate, which can serve as precursors of acetyl coA and succinyl coA
SALVAGE OF PYRIMIDINES
Pyrimidine salvage defects have not been clinically documented
Nucleic Acid Metabolism Overview
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