Purine Synthesis Flashcards
What type of nucleotides often act as second messengers?
Purines: cAMP and cGMP
What is made first DNA or RNA?
RNA as RNA is then coverted to DNA through removal of an OH group
Where does nitrogen come from?
Amino acids
What is the first step of purine synthesis?
Ribose 5-phosphate is converted into PRPP by PRPP synthetase
What nucleotide is made from PRPP?
IMP (this is then converted into AMP and GMP)
What base makes up Inosine monophosphate (IMP)?
Hypoxanthine
How many Carbons and double bonds do purines have?
2 rings
- 6 carbon ring with 3 double bonds
- 5 carbon ring with 2 double bonds
What is the rate limiting enzyme that converts PRPP to IMP?
Glutamine-PRPP amidotransferase
What inhibits Glutamine-PRPP amidotransferase?
This enzyme converts PRPP to IMP
IMP/AMP/GMP
What converts ADP and GDP to dADP and dGDP?
Ribonucleotide Reductase
What blocks the conversion of IMP to GMP?
Ribavirin (antiviral) and Mycophenolate (immunosuppressant)
What is purine salvage?
When bases Adenine, Guanine and Hypoxanthine are converted back into AMP, GMP and IMP (requires PRPP)
What enzyme converts Hypoxanthine (+PRPP) and Guanine (+PRPP) into IMP and GMP?
HGPRT
What converts Adenine (+PRPP) into AMP?
APRT
What does 6-MP (and its prodrug azathioprine) mimic?
Hypoxanthine/Guanine (creates a mutant nucleotide) and causes decreased purine nucleotides
What are Hypoxanthine and Guanine broken down into?
Xanthine and subsequently Uric acid
What is Hypoxanthine converted into Xanthine by?
Xanthine Oxidase
What is Guanine broken down into Xanthine by?
Guanase
WHat is Xanthine converted into Uric acid by?
Xanthine Oxidase
What base is adenosine converted into in order to break it down?
Hypoxanthine
What are the steps involved in Adenosine breakdown/ excretion?
- Adenine -> AMP (through APRT)
- AMP -> Adenosine
- Adenosine -> Inosine (thru Adenosine deaminase)
- Inosine -> Hypoxanthine (thru Purine nucleoside phosphorylase)
What is the difference between AMP and Adenine?
AMP has a phosphate and a sugar (ribose)
What converts Adenosine into Inosine?
Adenosine deaminse (amine group removed)
Difference between AMP and Adenosine?
Adenosine-MP has a Phosphate group
What enzyme is effected in Severe combines immunodifficiency syndrome?
Adenosine deaminase (Adenosine into Inosine)
What converts Inosine into Hypoxanthine?
Purine nucleoside phosphorylase
What does Xanthine Oxidase convert 6-MP into?
Thiouric acid (inactive)
Why does Allopurinol increase the effects of 6-Mp?
Inhibits Xanthine Oxidase thus inhibiting the breakdown of 6-MP into Thiouric acid
What converts Uric acid into Allantoin?
Urate oxidase (rasburicase)
