1.13 - Nucleic Acid Metabolism

Question 1

purpose of pentose shunt pathway (3)

Answer 1

1. maintain carbon homeostasis
2. provide precursors for nucleotide and amino acid biosynthesis
3. counter oxidative stress

Question 2

what are purines synthesised as?

Answer 2

the ribonucleotide (not as free bases)

Question 3

first step of purine nucleotide synthesis

Answer 3

activated form of ribose-5-phosphate (5-phosphoribosyl-1-pyrophosphate (PRPP))

Question 4

second step of purine nucleotide synthesis

Answer 4

replace the pyrophosphate of PRPP with an amine from glutamine

Question 5

first intermediate with full purine ring of synthesis of purine nucleotides

Answer 5

inosinate (inosine monophosphate (IMP))

Question 6

how does synthesis of inosinate (IMP) begin

Answer 6

addition of amine from glutamine to PRPP

Question 7

what are adenine and guanine synthesised from (IMP)

Answer 7

AMP and GMP respectively

Question 8

role of purine salvage pathways

Answer 8

will recycle any breakdown products of nucleic acids

Question 9

purine salvage pathway

Answer 9

free bases of adenine and guanine (and hypoxanthine) added to PRPP

Question 10

what % of daily purine nucleotide biosynthesis do salvage pathways account for?

Answer 10

90%

Question 11

why do salvage pathways account for more purine biosynthesis than de novo synthesis pathways?

Answer 11

salvage pathways require less energy

Question 12

first step of pyrimidine nucleotide synthesis

Answer 12

carbamoyl phosphate and aspartate lead to the synthesis of orotic acid (orotate)

Question 13

second step of pyrimidine nucleotide synthesis

Answer 13

5-phosphoribosyl-1-pyrophosphate (PRPP) added to orotic acid to give orotidine 5’-monophosphate (OMP)

Question 14

what is OMP used to synthesise? (4)

Answer 14

1. UMP
2. UDP
3. CTP
4. TTP

Question 15

inhibitor of pyrimidine nucleotide biosynthesis

Answer 15

5 fluorouracil inhibits thymidylate synthesis

Question 16

inhibitors of the enzyme for PRPP biosynthesis (purine nucleotide synthesis) (4)

Answer 16

1. ADP
2. GDP
3. AMP
4. GMP

Question 17

key intermediate for ATP and GTP synthesis

Answer 17

inosine mono phosphate (IMP)

Question 18

what are pyrimidines assembled as?

Answer 18

free bases

Question 19

key intermediate of UTP, CTP and dTTP

Answer 19

orotidine monophosphate (OMP)

Question 20

inhibitors of carbamoyl phosphate synthesis (2)

Answer 20

1. UDP
2. UTP

Question 21

waste product of break down of purines in food

Answer 21

uric acid

Question 22

what happens to most uric acid in the body?

Answer 22

dissolves in blood, filtered by kidneys and excreted in urine

Question 23

what happens when too much purine is present in the body

Answer 23

develop a condition known as hyperuricaemia (gout)

Question 24

gout

Answer 24

needle-shaped uric acid crystals form in and around joint resulting in acute pain

Question 25

what determines de novo synthesis of purine

Answer 25

level of uric acid in waste

Question 26

% purine recycled under physiological condition

Answer 26

90%

Question 27

what does purine recycling prevent?

Answer 27

them from going down uric acid production

Question 28

result of non-physiological condition in purine recycling

Answer 28

reduced as result of malfunction in one or more steps

Question 29

result of non-physiological condition in de novo purine synthesis pathway

Answer 29

increase

Question 30

role of allopurinol

Answer 30

decreases amount of uric acid produced in the body

Question 31

how does allopurinol decrease the amount of uric acid produced in the body?

Answer 31

blocks the conversion of hypoxanthine to xanthine and encourages salvage pathway