Purine Synthesis

Question 1

What type of nucleotides often act as second messengers?

Answer 1

Purines: cAMP and cGMP

Question 2

What is made first DNA or RNA?

Answer 2

RNA as RNA is then coverted to DNA through removal of an OH group

Question 3

Where does nitrogen come from?

Answer 3

Amino acids

Question 4

What is the first step of purine synthesis?

Answer 4

Ribose 5-phosphate is converted into PRPP by PRPP synthetase

Question 5

What nucleotide is made from PRPP?

Answer 5

IMP (this is then converted into AMP and GMP)

Question 6

What base makes up Inosine monophosphate (IMP)?

Answer 6

Hypoxanthine

Question 7

How many Carbons and double bonds do purines have?

Answer 7

2 rings

• 6 carbon ring with 3 double bonds
• 5 carbon ring with 2 double bonds

Question 8

What is the rate limiting enzyme that converts PRPP to IMP?

Answer 8

Glutamine-PRPP amidotransferase

Question 9

What inhibits Glutamine-PRPP amidotransferase?

This enzyme converts PRPP to IMP

Answer 9

IMP/AMP/GMP

Question 10

What converts ADP and GDP to dADP and dGDP?

Answer 10

Ribonucleotide Reductase

Question 11

What blocks the conversion of IMP to GMP?

Answer 11

Ribavirin (antiviral) and Mycophenolate (immunosuppressant)

Question 12

What is purine salvage?

Answer 12

When bases Adenine, Guanine and Hypoxanthine are converted back into AMP, GMP and IMP (requires PRPP)

Question 13

What enzyme converts Hypoxanthine (+PRPP) and Guanine (+PRPP) into IMP and GMP?

Answer 13

HGPRT

Question 14

What converts Adenine (+PRPP) into AMP?

Answer 14

APRT

Question 15

What does 6-MP (and its prodrug azathioprine) mimic?

Answer 15

Hypoxanthine/Guanine (creates a mutant nucleotide) and causes decreased purine nucleotides

Question 16

What are Hypoxanthine and Guanine broken down into?

Answer 16

Xanthine and subsequently Uric acid

Question 17

What is Hypoxanthine converted into Xanthine by?

Answer 17

Xanthine Oxidase

Question 18

What is Guanine broken down into Xanthine by?

Answer 18

Guanase

Question 19

WHat is Xanthine converted into Uric acid by?

Answer 19

Xanthine Oxidase

Question 20

What base is adenosine converted into in order to break it down?

Answer 20

Hypoxanthine

Question 21

What are the steps involved in Adenosine breakdown/ excretion?

Answer 21

• Adenine -> AMP (through APRT)
• AMP -> Adenosine
• Adenosine -> Inosine (thru Adenosine deaminase)
• Inosine -> Hypoxanthine (thru Purine nucleoside phosphorylase)

Question 22

What is the difference between AMP and Adenine?

Answer 22

AMP has a phosphate and a sugar (ribose)

Question 23

What converts Adenosine into Inosine?

Answer 23

Adenosine deaminse (amine group removed)

Question 24

Difference between AMP and Adenosine?

Answer 24

Adenosine-MP has a Phosphate group

Question 25

What enzyme is effected in Severe combines immunodifficiency syndrome?

Answer 25

Adenosine deaminase (Adenosine into Inosine)

Question 26

What converts Inosine into Hypoxanthine?

Answer 26

Purine nucleoside phosphorylase

Question 27

What does Xanthine Oxidase convert 6-MP into?

Answer 27

Thiouric acid (inactive)

Question 28

Why does Allopurinol increase the effects of 6-Mp?

Answer 28

Inhibits Xanthine Oxidase thus inhibiting the breakdown of 6-MP into Thiouric acid

Question 29

What converts Uric acid into Allantoin?

Answer 29

Urate oxidase (rasburicase)