Quiz 1 (Nucleotide Metabolism)

Question 1

Nucleotides are ___ nucleosides.

Answer 1

Phosphorylated

• nucleoside = nitrogenous base + sugar
• nucleotide = nitrogenous base + sugar + phosphate(s)

Question 2

What is used in DNA synthesis, but not RNA sysnthesis?

A. ADENINE
B. GURANINE
C. THYMINE
D. CYTOSINE
E. URACIL

Answer 2

C. THYMINE

*Uracil is used in RNA synthesis instead

Question 3

What is the role of nucleotide sugars in the body?

A. They act as activated monosaccharide donors
B. They are used in glycogen synthesis
C. They are used in glycoprotein synthesis
D. All of the above

Answer 3

D.

Question 4

The activation of ribose-5-phosphate is done by the enzyme ___ which requires ATP.

Answer 4

PRPP Synthetase

Question 5

The committed step of purine synthesis is the formation of ___ from ___.

Answer 5

PRA / PRPP

Question 6

The formation of IMP is inhibited by ___.

Answer 6

Methotrexate

Question 7

The formation of ATP during purine synthesis also forms ___ which goes into the TCA cycle.

Answer 7

Fumarate

Question 8

What is cross-regulation during nucleotide synthesis?

Answer 8

When the need of one nucleotide is coupled to another

Ex: AMP synthesis is stimulated by GTP synthesis

Question 9

During pyrimidine synthesis, the ___ is built first and then PRPP is added.

Answer 9

Pyrimidine ring

Question 10

The rate limiting step in pyrimidine synthesis involves the formation of ___ by CPS-II.

Answer 10

Carbamoyl phosphate

Question 11

Disfunctions in UMP Synthetase can result in ___.

Answer 11

Orotic Aciduria

Question 12

dUTP is highly regulated so that it ___.

Answer 12

Does not get incorporated into DNA

Question 13

IMP —> ?

UMP —> ?

Answer 13

IMP —> purines (A/G)

UMP —> pyrimidines (T/C/U)

Question 14

Defects in CPS-I result in ___ whereas defects in CPS-II result in ___.

Answer 14

Hyperammonemia / ?

• CPS-I = allows NH4+ to enter the Urea Cycle
• CPS-II = allows for the formation of pyrimidines

Question 15

___ is a key antioxidant regulated by the formation of NADPH from the Pentose Phosphate Pathway.

Answer 15

Glutathione

Question 16

Methotrexate can be used to inhibit ___ in rapidly dividing cancer cells by preventing the formation of ___.

Answer 16

DNA replication / dTMP

Question 17

Sulfa drugs selectively disrupt DNA synthesis in ___ by inhibiting the formation of ___.

Answer 17

Bacteria / folate

Question 18

Purine catabolism converges to form ___ which is largely converted to Uric Acid by the enzyme ___.

Answer 18

Xanthine / Xanthine Oxidase

*buildup of Uric Acid leads to Gout

Question 19

___ can target Xanthine Oxidase to inactive it so that Uric Acid is not made in excess.

Answer 19

Allopurinol

Question 20

Overproduction of ___ can lead to hemolytic anemia, while under production can lead to SCID (“bubble boy syndrome”).

Answer 20

ADA (Adenosine Deaminase)

*is responsible for deaminating Adenosine in purine catabolism

Question 21

___ is the endpoint of purine catabolism.

Answer 21

Uric Acid

Question 22

Limit dietary intake of ___ is used to treat gout.

Answer 22

Purines

*or use of Allopurinol to inhibit Xanthine Oxidase

Question 23

Salvage pathways dominated de novo synthesis of ___.

Answer 23

Purines

• APRT regenerates AMP
• HGPRT regenerates GMP / IMP (deficiency —> Lesh-Nyhan Disease)

Question 24

The activity of HGPRT contributes to ___ a disease characterized by self-destructive behavior.

Answer 24

Lesh-Nyhan Disease

*HGPRT regenerates purines excessively

Question 25

The antiviral agent ___ structurally resembles guanine.

Answer 25

Acyclovir

*thymadine kinase from a virally-infected cell will use it to make DNA, but it will block DNA synthesis

Question 26

In Severe Combined Immunodeficiency Disease (SCID), the enzyme ___ is deficient.

Answer 26

Adenosine Deaminase (ADA)

*deficiency in ADA results in buildup of dATP which inhibits ribonucleotide reductases (inhibits production of other dNTPs)

Question 27

____ is an inhibitor of Xanthine Oxidase and is used to treat ___.

Answer 27

Allopurinol / GOUT

Question 28

Treatment of Orotic Aciduria involves a uridine diet. How does this affect the disease?

Answer 28

• exogenous uridine can be converted to UMP by phosphotransferase
• UTP made from the exogenous uridine provides the substrate for CTP synthesis
• UTP made from the exogenous uridine can inhibit CPS-II

Question 29

What is true of de novo synthesis of pyrimidine nucleotides?

A. All reactions take place in the cytosol
B. UMP and CMP are formed from a common intermediate
C. PRPP is required in the rate limiting step
D. UMP-mediated inhibition of OMP decarboxylase is the major mechanism of control
E. A free base is formed as the intermediate

Answer 29

E.

A. No - one step occurs in the mitochondria
B. No - UMP is eventually converted to CTP, however CMP is not part of that process
C. No - PRPP is the RLS for purine synthesis, not pyrimidine synthesis
D. No - OMP decarboxylation is done by UMP Synthase which is not the main regulatory step (CPS-II is the major step regulated by UMP)

Question 30

Deoxyribonucleotides are synthesized by an enzyme system involving ___.

Answer 30

Thioredoxin