Lecture 13 - Nucleic Acid Metabolism

Question 1

purines are synthesised as:

Answer 1

ribonucleosides (not as free bases)

Question 2

what bases are double ringed and what ones are singularly ringed?

Answer 2

pyrimidines are single ringed and purines are double ringed

Question 3

first step in purine biosynthesis:

Answer 3

first step is the synthesis of the activated form of ribose-5-phosphate - 5-phosphoribosyl-1-pyrophosphate (PRPP)

Question 4

what is the purpose of the penrose phosphate pathway?

Answer 4

The purpose of this pathway is:
•to maintain carbon homoeostasis, to provide precursors for nucleotide & amino acid biosynthesis
•to provide reducing molecules for anabolism
•to counter oxidative stress

Question 5

what is the second step of purine biosynthesis?

Answer 5

the second step of purine biosynthesis is to replace the pryophosphate of PRPP with an amine from glutamine

Question 6

what happens after multiple steps in de novo purine nucleotide biosynthesis?

Answer 6

after multiple steps you have inosinate (IMP) also known as inosine monophosphate

Question 7

what is the first intermediate with a full purine ring in the synthesis of inosine monophosphate?

Answer 7

The first intermediate with full purine ring is Inosinate also known as Inosine Monophosphate (IMP)

Question 8

what does the synthesis of IMP begin with?

Answer 8

Synthesis of IMP begins with addition of amine from glutamine to PRPP

Question 9

Adenine and Guanine are synthesised from:

Answer 9

IMP as AMP and GMP, respectively

Question 10

Any breakdown products of nucleic acid will be recycled by:

Answer 10

purine salvage pathways where simply free bases of adenine and guanine are attached to PRPP

Question 11

what do savage pathways account for?

Answer 11

salvage pathways account for 90% of daily purine nucleotide biosynthesis

Question 12

what pathway requires less or more energy in nucleotide biosynthesis?

Answer 12

Salvage pathways require less energy than de novo synthesis pathway for purine synthesis

Question 13

Pyrimidine synthesis starts from:

Answer 13

Carbamoyl phosphate, that leads to the synthesis of orotic acid (a.k.a. orotate)
•5-phosphoribosyl-1-pyrophosphate (PRPP) is added to orotic acid to give orotidine 5’-monophosphate (OMP)
•OMP is used to synthesise UMP, UDP, CTP, and TTP

Question 14

what are purines synthesised as?

Answer 14

purines are synthesised as ribonucleosides

Question 15

what inhibits the enzyme for PRPP biosynthesis?

Answer 15

ADP, GDP, AMP, and GMP all inhibit the enzyme for PRPP biosynthesis

Question 16

what is the key intermediate for ATP & GTP synthesis?

Answer 16

Inositol mono phosphate, IMP is the key intermediate for ATP and GTP synthesis

Question 17

UDP and UTP inhibit the synthesis of:

Answer 17

carbamoyl phosphate

Question 18

uric acid:

Answer 18

•Uric acid is a waste product as the result of breaks down of purines in food

•Most uric acid dissolves in blood and filtered by the kidneys and excreted in urine

•When too much purine is present in the system, we develop a condition known as hyperuricaemia. A.k.a. Gout

•Needle-shaped uric acid crystals form in and around the joint resulting in acute pain.

Question 19

de novo synthesis of purine is determined by:

Answer 19

the level of uric acid in waste

Question 20

allopurinol:

Answer 20

allopurinol decreases the amount of uric acid produced by the body

•Purines are generally higher in high-protein foods. In the body, purines are converted to uric acid.

•Allopurinol blocks this conversion of hypoxanthine to xanthine and encourage the salvage pathway.