Nucleotide Metabolism

Question 0

What are the three structures of a nucleotide?

Answer 0

Pentose sugar, nitrogenous base, phosphates

Question 1

What are polymers of nucleotides?

Answer 1

Nucleic acids

Question 2

What is a base + sugar?

Answer 2

nucleoside

Question 3

What are the two purines?

Answer 3

adenine and guanine

Question 4

What are the three pyrimidines?

Answer 4

thymine, cytosine, and uracil

Question 5

What are some of the uses of nucleotides? (5)

Answer 5

1. Energy currency
2. Phosphate source
3. Coenzymes
4. Substrate activators
5. 2nd messengers

Question 6

What is an important intermediate in the biosynthesis of purines?

Answer 6

PRPP

Question 7

PRPP is formed from ribose-5-phosphate. What enzyme is used? Activator? Inhibitor?

Answer 7

PRPP synthetase; inorganic phosphate; ADP

Question 8

The base of what is built upon a molecule of PRPP?

Answer 8

A purine ring

Question 9

Where do the carbons in a purine ring come from?

Answer 9

glycine, folate derivatives, and CO2

Question 10

Where do the nitrogens in a purine ring come from?

Answer 10

glycine, aspartate, and glutamine

Question 11

What is the first purine formed in the ten-step process?

Answer 11

IMP - inosine monophosphate

Question 12

How many high energy bonds are required in purine synthesis?

Answer 12

6

Question 13

AMP and GMP are formed from what?

Answer 13

IMP

Question 14

What amino acid provides a nitrogen to IMP in the formation of adenosine?

Answer 14

aspartate

Question 15

In the formation of guanosine, glutamine provides a nitrogen to what?

Answer 15

xanthosine

Question 16

Where are the enzymes that construct the purine ring system?

Answer 16

cytosol, namely the liver, which secretes free bases and nucleosides

Question 17

What are the first two steps of purine synthesis?

Answer 17

PRPP sythesis and amidotransferase

Question 18

What is the committed step of purine synthesis?

Answer 18

2nd step - PRPP amidotransferase

Question 19

What cells are reliant on purine recycling?

Answer 19

brain, lymphocytes, neutrophils

Question 20

Purine rings are recycled by what?

Answer 20

re-attachment to PRPP

Question 21

In purine recycling Adenine phosphoribosyl transferase forms what from adenine?

Answer 21

AMP

Question 22

In purine recycling hypoxanthine-guanine phosphoribosyl transferase (HGPRT) recycles H and G to form what?

Answer 22

Hypoxanthine > IMP

Guanine > GMP

Question 23

What are the original ring components of pyrimidines?

Answer 23

glutamine, aspartate, and CO2

Question 24

What enzyme forms UMP?

Answer 24

CPS-II carbomoyl phosphate synthetase

Question 25

Where is UMP formed?

Answer 25

Cytosol and mitochondria

Question 26

What is required in the formation of CTP from UTP?

Answer 26

glutamine

Question 27

Deoxyribonucleotides are formed by reduction of what?

Answer 27

ribonucleotide disphosphates

Question 28

What is the product of purine breakdown?

Answer 28

Uric acid

Question 29

What is the key enzyme in the degradation of purines and pyrimidines?

Answer 29

Xanthine oxidase

Question 30

What are the cofactors in the degradation of purines and pyrimidines?

Answer 30

O2, molybdenum, iron, sulfur

Question 31

Beta-alanine and beta-aminoisobutyrate are the final products of what?

Answer 31

pyrimidine degradation

Question 32

What are used to treat neoplasms?

Answer 32

Inhibitors of nucleotide metabolism

Question 33

We don't store nucleotides, so what happens if we have extra?

Answer 33

They get degraded

Question 34

What are the three inhibitors of nucleotide metabolism?

Answer 34

Structural analog, antifolates, glutamine antagonists

Question 35

What is a folic acid analog?

Answer 35

methotrexate

Question 36

Gout results from what?

Answer 36

Deposition of sodium urate crystals in the joints and kidneys

Question 37

What is defective in gout? (2)

Answer 37

PRPP synthetase is abnormal in some cases; HGPRT may be partially deficient in others

Question 38

In gout, leukocytes take up crystals and what happens next?

Answer 38

They rupture, releasing lysosomal enzymes which inflame and erode joints. Uric acid crystals in the kidney impair renal function

Question 39

What blocks formation of uric acid crystals through suicide inhibition of xanthine oxidase?

Answer 39

Allopurinol

Question 40

de novo purine synthesis is decreased by the reaction of what two things?

Answer 40

PRPP with allopurinol

Question 41

What is an anti-inflammatory used to reat gout which inhibits leukocyte movement?

Answer 41

Colchicine

Question 42

What inhibits organic ion transport? (gout)

Answer 42

Probenicid

Question 43

What condition is associated with x-linked recessive, deficiency of HGPRT activity?

Answer 43

Lesch-Nyhan syndrome

Question 44

In lesch-nyhan syndrome, intracellular levels of PRPP increase, IMP and GMP decrease. What does this lead to?

Answer 44

Increase in de novo purine synthesis

Question 45

What are some of the symptoms of lesch-nyhan syndrome?

Answer 45

gout, hyperuricemia, urinary tract stones, mental retardation, self-mutilation, spasticity

Question 46

PRPP cannot react with allopurinol, so in treating lesch-nyhan syndrome, de novo purine synthesis does not decrease. What is reduced? What is not reduced?

Answer 46

gout; mental symptoms

Question 47

What is deficient in glycogen storage disease type I (von gierke's)?

Answer 47

Glucose-6-phosphatase

Question 48

What two things are increased in glycogen storage disease type I (von Gierke's)?

Answer 48

ribose-5-phosphate and PRPP

Question 49

In glycogen storage disease type I (von gierke's) is de novo purine synthesis increased or decreased?

Answer 49

increased

Question 50

What condition is associated with the following?: 1. defective conversion of orotate or orotidine monophosphate to UMP 2. reduced DNA and RNA synthesis results leading to sever anemia 3. treatment with uridine can be effective

Answer 50

Orotic aciduria