Chapter 25: Purines and Pyrimidines

Question 1

Know the source of each atom in the pyrimidine ring (bicarbonate, aspartate, and ammonia).

Question 2

Know that the pyrimidine ring is made and THEN bonded to the ribose, whereas the purine ring made on the ribose.

Question 3

Know that we add the pyrimidine ring to 5-phosphoribosyl-1-pyrophosphate, with PPi as the leaving group.

Answer 3

Pyrimidine ring + PRPP–> PPi + ring and sugar

Question 4

Know that the Purine synthesis is expensive in terms of ATP and this is why the salvage pathway is of such great value

Question 5

Describe the regulation of pyrimidine and purine synthesis (pg 837 copied from the book into the notes (April 26).

Answer 5

ATCase is the control point.

-ATP activates.
-CTP inhibits. (feedback inhibition).

Question 6

Know that HMG-CoA reductase is the key control point of cholesterol biosynthesis.