Week 2 RAS live Lecture 5

Question 1

1) How are pyrimidines assembled?

Answer 1

1) Ring first, then ribose attaches

Question 2

2) How are Purines assembled?

Answer 2

2) Ribose first, then ring

Question 3

3) What is the core pathway for purines?

Answer 3

3) Ribose-5-p PRPPphosphoribosy-lamineIMP

Question 4

4) What is the full pathway for purines?

Answer 4

4) Ribose-5-p PRPP
a)  Deamination of PRPP into PRA (energy from PRPP )
b) Glycine + PRA into GAR (uses the carboxylate group of glycine + requires ATP)
c) GAR into FGAR by adding C1 via FH4
d) FGAR into FGAM by adding NH2 (from glutamine)
e) FGAM into AIR (ring closure)
f) AIR into CAIR (CO2 attaches to the first NH2 then it rearranges)
g) CAIR into SAICAR by addition of aspartate and ATP (aspartate donates NH2)
h) SAICAR into AICAR (fumarate leaves)
i) AICAR into FAICAR (addition of C1 via FH4)
j) FAICAR intp IMP (ring closure, loss of water)phosphoribosy-lamineIMP

Question 5

5) How is PRPP formed?

Answer 5

5) Ribose-5-P + ATP 5-phosphoribosyl-1-pyrophosphate (PRPP) + AMP Using ribosephosphate pyrophosphokinase

Question 6

6) Where does ribose-5-p come from?

Answer 6

6) Pentose Phosphate pathway

Question 7

7) How can the formation of PRPP downregulated?

Answer 7

7) By ADP and GDP

Question 8

8) The reactions 2-7 of purine biosynthesis are homologous, what are the common steps, and how do they usually work?

Answer 8

8) 2 steps:
a) Activation of an oxygen atom (usually ATP): The lone pair of the oxygen will attack the slightly positive phosphate,
b) Attack by a nucleophile (ammonia or an amine group): nucleophile attacks the activated carbon.

Question 9

9) Where do the components of a purine ring come from?

Answer 9

9) 2 glutamines, 2 Formates (FH4), aspartate, glycine and CO2

Question 10

10) How is IMP made into AMP?

Answer 10

10) By adding Aspartate, GTP to IMP  making AMP, GDP and fumarate

Question 11

11) How is ribonucleotide converted into deoxyribonucleotide?

Answer 11

11) By NADPH using ribonucleotide reductase as enzyme.

Question 12

12) What can work as an NH2 Donor?

Answer 12

12) Aspartate, by product is fumarate

Question 13

13) What does amination always require?

Answer 13

13) Energy

Question 14

14) What is the overall control for purine biosynthesis?

Answer 14

14) IMP (AMP, GMP) negative inhibition

Question 15

15) How are the end products controlled (ATP and GTP)?

Answer 15

15) ATP activates the production of GTP, and GTP activates the production of ATP