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Medical Biochemistry > 5- Pyrimidine nucleotide metabolism > Flashcards

5- Pyrimidine nucleotide metabolism Flashcards

1
Q

Wha is CAD in eukaryotes ?

A

It is a multienzyme complex made from : Carbamoyl phosphate synthetase II, Aspartate transcarbamoylase and Dihydrooratase .

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2
Q

What is the first reaction of the pyrimidine biosynthesis ?

A

The synthesis of carbamoyl phosphate

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3
Q

How is the carbamoyl phosphate is synthesized ?

A

from γ- amino of Gln
and CO2 by cytosolic carbamoyl phosphate synthetase II in
expense of two moles of ATP.

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4
Q

What is the first step in urea biosynthesis ?

A

carbamoyl phosphate
synthetase I

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5
Q

What is the difference between carbamoyl phosphate synthetase-I and carbamoyl phosphate synthetase-II ?

A
  • Cellular location : mitochondria / cytosol
  • metabolic pathway : urea cycle / pyrimidine synthesis
  • nitrogen source : ammonia / glutamine
  • regulator : activator (N-Acetyl-glutamate) / activator (PRPP) , inhibitor (UTP)
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6
Q

What happens in the aspartate transcarbamoylase (ATCase) reaction ?

A

It will transfer carbamoyl group to the a-
amino group of an aspartate for the biosynthesis of carbamoyl aspartate.

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7
Q

What is the allosteric enzyme and regulates the rate of the pyrimidine bosynthesis ?

A

ATCase

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8
Q

What happen in the dihydroorotase reaction ?

A

Ring closure occurs by removal of a mole of water from carbamoylaspartate by
dihydroorotase and the pyrimidine derivative, L- dihydroorotate is synthesized.

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9
Q

What happens in the reaction mechanism of dihydroorotate dehydrogenase in the eukaryotic cells ?

A

a pair of hydrogen is extracted from dihydroorotate (it isoxidized) and orotate is formed in pyrimidine biosynthesis only this reaction occurs in mitochondria.

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10
Q

What happens in the orotate phosphoribosyltransferase reaction ?

A

Ribose-5-phosphate in PRPP is
fused from its first carbon to the first
amide nitrogen in the structure of
orotate to form OMP (Orotidine - 5’
–phosphate). OMP (Orotidylate) is the
first pyrimidine nucleotide
synthesized.

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11
Q

What is the difference in the regulation pyrimidine biosynthesis in E. coli and
animal cells ?

A

in E. coli at control step ATCase whereas in animal cells at control step carbamoyl phosphate synthetase II is found.

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12
Q

How will the Pyrimidine phosphoribosyltransferase will synthesize new pyrimidine nucleotides ?

A

using pyrimidine bases released from RNA and DNA degradation.

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13
Q

What are the deoxyribonucleotides ?

A

The structural units of the DNA

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14
Q

Where are deoxyribonucleotides are derived from ?

A

From corresponding ribonucleotides by reduction at the 2’ carbon of the ribose .

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15
Q

What are reduction reactions and what is its catalyzer ?

A

It is the unusual reduction occuring at an unactivated carbon and its catalyzed by the ribonucleotide reductase .

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16
Q

What is the substrates of biosynthesis of deoxyribonucleotides ?

A

ribonucleoside diphosphates (NDP).

17
Q

What are the two carries of proteins During the reduction of D-riboses to deoxy D-riboses of a pair of hydrogen atoms from NADPH to D-riboses of the NDPs ?

A
  1. Thioredoxin
  2. Glutaredoxin
18
Q

How is ribonucleotide reductase is regulated ?

A

its substrate specificity is regulated by the binding of effector molecules.

19
Q

What happens in the regulation at primary activity regulatory site ?

A

ATP function as the activator, dATP as the inhibitor for conversion
of CDP, UDP, GDP and ADP to dCDP, dTTP, dGDP and dADP .

20
Q

What happens in the regulation at substrate specificity regulatory site ?

A
  • If ATP or dATP bind to substrate specificity regulatory site, enzyme will prefere to reduce CDP and UDP to dCDP and dUDP (dTTP).
  • If dTTP or dGTP bind substrate specificity regulatory site, enzyme will prefere to reduce GDP and ADP to dGDP and dADP .
21
Q

What is required for the biosynthesis of thymine nucleotide ?

A

dTMP, dUMP

22
Q

What converts dUMP ti dTMP ?

A

Thymidylate synthase

23
Q

How is biosynthesis of thymine nucleotide ?

A

is controlled by dCTP deaminase.

24
Q

What is the allosteric modulators of the biosynthesis of thymine nucleotide ?

A

dCTP is the positive and dTTP is the negative allosteric modulator.

Medical Biochemistry (5 decks)

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