Week 6: Purine and Pyrimidine Biosynthesis

Question 1

Purine biosynthesis

Answer 1

PPP -> NADPH + Ribose-5-phosphate

Ribose-5-phosphate if Ribose-5-phosphate is not needed then returned to glycolysis into fructose-6-phosphate and to Glyceraldehyde-3-phospate to oxidize into energy in the glycolytic pathway

If Ribose-5-phosphate is needed:

Ribose-5-phosphate + ATP x-PRPP Synthase (5-Phosphoribosyl-1-phosphate synthase)-> PRPP( 5-Phosphoribosyl-1-phosphate) + ADP

PRPP + Purine ring on C1 –> Inosine Monophosphate (IMP)

IMP -> AMP or GMP

Question 2

PPP AKA

Answer 2

Pentose Phosphate Pathway

Question 3

Purine synthesis regulation

Answer 3

• Ribose-5-phosphate + ATP x-PRPP Synthase (5-Phosphoribosyl-1-phosphate synthase)-> PRPP( 5-Phosphoribosyl-1-phosphate) + ADP
  
  • This step is regulated by purines ([AMP] and [GMP]) inhibit PRPP synthase blocking the Ribose-5-phosphate into the purine synthesis pathway and shunt it into the glycolytic pathway to generate energy

Question 4

Pyrimidine Biosynthesis

Answer 4

synthesize the ring structure without the ribose and then add it to PRPP to construct Orotate (uses AAs and small molecules such as carbamoyl phosphate to close up the ring)

Orotate + PRPP -orotate phosphoribosyl transferase-> Uridine monophosphate (UMP)

UMP –> CMP or TMP (Cytosine monophosphate or Thymidine monophosphate)

Question 5

Pyrimidine Biosynthesis regulation

Answer 5

• genetic error in Orotate phosphoribosyl transferase will lead to orotate aciduria because cant add orotate to PRPP so orotate will build-up
  
  • orotate is an acid from carboxylic acid
  • inborn genetic error