De Novo Synthesis of Purines

Question 1

What steps of purine synthesis consume ATP?

Answer 1

Steps 2, 4, 5, 6, & 8

Question 2

Describe step 1 of purine de novo synthesis

Answer 2

• A nitrogen atom from glutamine is added on to PRPP by glutamine-PRPP amidotransferase
• The product from this step is highly unstable making it ready to react in the following step
  This is the rate limiting step

Question 3

Describe step 2 of purine de novo synthesis

Answer 3

Take glycine and ATP and start to the ring (3 carbons added)

Question 4

Describe step 3 of purine de novo synthesis

Answer 4

Add a carbon atom from N10-Formyl-THF (derived from formate)

Question 5

Describe step 4 of purine de novo synthesis

Answer 5

Add another nitrogen from glutamine using ATP

Question 6

Describe step 5 of purine de novo synthesis

Answer 6

Consume ATP one more time to form the first 5-membered ring
3 of the 6 atoms needed for the second ring of the purine structure are in place

Question 7

Describe step 6 of purine de novo synthesis

Answer 7

Carbon atoms from CO2 are added using ATP
In humans step 7 is skipped, resulting product is carboxyamino imidazole ribonucleotide

Question 8

Describe step 8 and 9 of purine de novo synthesis

Answer 8

Add amino group from aspartate using ATP

Question 9

Describe step 10 of purine de novo synthesis

Answer 9

Add a carbon from N10-formyl-THF

Question 10

Describe step 11 of purine de novo synthesis

Answer 10

A second ring closure takes place and the inosinate (IMP) precursor is formed