Exam 1 Flashcards
What is the key precursor in the synthesis of Purines and Pyrimidines?
PRPP
Purines are formed at what kind of level?
They are formed at the nucleotide level, starting with PRPP.
Pyrimidines are synthesized at what kind of level?
They are synthesized at the base level with the conversion to a nucleotide occurring late in the pathway.
Ribonucleotides are precursors for what?
Deoxyribonucleotides.
What is the main branch point in purine biosynthesis?
The production of inosine 5-monophosphate. - IMP
What compounds make up a purine ring when synthesis is de novo?
Aspartate -> 1 Nitrogen
Glutamine -> 2 Nitrogen
Formate -> 2 Carbons
Glycine -> 2 Carbons and 1 Nitrogen
What is another way that IMP can be produced, instead of using PRPP?
Through amino acids.
PRPP can be synthesized with what?
5-Carbon Sugars
Purine Reaction 1: IMP Production
Glutamine-PRPP Amidotransferase
Cofactors: Glutamine -> Glutamine + PPi
Addition of Nitrogen
Purine Reaction 2: IMP Production
GAR Syntetase
Cofacters: Glycine + ATP -> ADP + Pi
Addition of 2 Carbon and 1 Nitrogen (the whole structure of glycine)
Purine Reaction 3: IMP Production
GAR Transformlyase
Cofactors: Formate Derivative -> Formate Derivative
Addition of 1 Carbon
Purine Reaction 4: IMP Production
FGAR Amidotransferase
Cofactors: Glutamine + ATP -> Glutamate + ADP + Pi
Addition of 1 Nitogen
Purine Reaction 5: IMP Production
FGAM Clycase
Cofactors: ATP -> ADP + Pi + H2O
Cyclization of the compound to form a ring.
Purine Reaction 6: IMP Production
AIR Carboxylase
Cofactors: HCO3 + ATP -> ADP + Pi
Addition of 1 Carbon
Purine Reaction 7: IMP Production
CAIR Mutase
Cofactors: None
Rearranges molecule.
Purine Reaction 8: IMP Production
SAICAR Synthetase
Cofactors: Aspartate + ATP -> ADP + Pi
Addition of 4 Carbons and 1 Nitrogen
Purine Reaction 9: IMP Production
SAICAR Lyase
Cofactors: None
Loss of Fumarate -> Most of that aspartate that was added before this step was lost, only the nitrogen was kept.
Purine Reaction 10: IMP Prodution
AICAR Transformylase
Cofactors: Formate Derivative -> Formate Derivative
Addition of 1 Carbon
Purine Reaction 11: IMP Production
IMP Synthase
Cofactors: None
Loss of water, following cyclization. FINAL END PRODUCT! IMP IS FORMED!
Describe the pathway from IMP to AMP.
Reaction 1: Addition of aspartate (which will be the nitrogen source) through the use of a GTP.
Reaction 2: Loss of fumarate, leaving back an amine group, forming AMP.
Describe the pathway from IMP to GMP.
Reaction 1: Addition of water forms a ketone on the ring with the oxidizing power of NAD+.
Reaction 2: Addition of glutamine (nitrogen source) with the help of ATP, forming GTP.
What bases are purines?
Guanine and Adenosine.
How is the biosynthesis of Purines regulated?
Via allosteric feedback control of purine biosynthetic enzymes by BOTH intermediates sand end products.
What is HGPRT and what does it do?
It is an enzyme that is apart of the purine salvage pathway. It catalyzes the reactions:
Guanine -> GMP
Hypoxantine -> IMP
To reuse the end products of GMP and AMP to create more nucleotides.
If HGPRT was not present, what would the fate of GMP and AMP be?
They would be converted to Uric Acid which can cause many diseases.
What molecules make up a pyrimidine ring?
Carbamoly-P and Aspartate
What molecule gets made before being added to PRPP in pyrimidine synthesis?
Orotate, the basic pyrimidine ring.
