Lect 9 Nucleotide Metabolism

Question 1

Nucleoside

Answer 1

Base + Sugar

Question 2

Nucleotide

Answer 2

Base + Sugar + Phosphate

Question 3

Purines

Answer 3

Pure As Gold (Ring)

Double Ring

Adenine & Guanine

Xanthine & Hypothanxine

Question 4

Pyrimidine

Answer 4

CUt The Pye

Single Ring

Cytosine & Thymine

Uracil

Question 5

What are 3 Roles of Nucleosides and Nucleotides

Answer 5

Components of Cofactors

Regulatory Roles

Important biomolecules

Question 6

What is the overall Purine Nucelotide Synthesis process?

Answer 6

Sugar Molecule Synthesis —> Ring Formation

Question 7

What occurs in Purine synthesis Phase I?

What enzyme is used?

Answer 7

Ribose 5P Activation

Ribose 5P –> PRPP/Phosphoribosyl pyrophosphate

(PRPP Synthetase)

Question 8

Purine Phase II

What is the enzyme?

Why is this step special?

Answer 8

Convert PRPP to PRA (Phosphoribosylamine)

Glutamine Phosphoribosyl Pyrophosphate Amidotransferase (GPPA)

Rate Limiting Step

Question 9

Purine Phase III

Why is methotrexate an inhibitor?

Why is it an anticancer drug?

Answer 9

Construct IMP Ring (PRA –> IMP in 9 Steps)

Methotrexate inhibits (competitive) oxidation of NADPH by DHFR/Dihyrofolate Reductase

Methotrexate: Competitive Inhibitor of enzymes utilizing folate (disrupts DNA replication in rapidly dividing cell)

Question 10

Purine Phase IV

Answer 10

Convert IMP to AMP and GMP

Question 11

What are Sulfa Drugs and what are their importance?

Answer 11

Competitive inhibitors of bacterial enzyme incorporating PABA into folate

Dirsupts DNA replication selectivley in bacteria

Question 12

Feeback Inhibition

Purine inhibition example

Answer 12

Accumulation of end product inhibit own synthesis

PRPP: inhibitted by IMP, AMP, GMP

Question 13

Cross Regulation

Answer 13

Synthesis is stimulated by production of other substrate

AMP synthesis stimulated by GTP

GMP stimulated by ATP

Question 14

Pyrimidine Nucleotide Synthesis Overall View

Answer 14

Pyrimidine Ring Formation –> Sugar Attachment

Sources: HCO3-, Gln, Asp, N, N-methylene THF

Cytosol and Mitochondria

Question 15

What does Pyrimidine Synthesis Phase I consist of?

What is the rate limiting step?

Answer 15

Formation of the orotate ring –> Committed Step

Carbamoyl phosphate + Asp –> carbamoyl aspartate via aspartate transcarbamoylase

Question 16

What does Pyrimidine Synthesis Phase II consist of?

What is orotic aciduria? and how is it treated?

Answer 16

Attach PRPP to Orotate Ring form UMP

Orotic Aciduria: Deficiency of UMP synthase

Tx: Oral Uridine

Question 17

What occurs in Pyrimidine Synthesis Phase III?

What is 5-fluorouracil and what does it do?

Answer 17

Convert UMP –> uridine, ctyosine, and thymidine (deoxy)nucelotides

(anticancer agent) inhibits thymidylate synthase (dUMP–>dTMP) and stops DNA production

Question 18

What does Thymidine Kinase do?

What is the mechanism of Acyclovir (Antiviral)

What is it used for?

Answer 18

• Phosphorylates dT –> dTMP –> DNA
• Acyclovir (resembles guanine) is phosphorylated by viral thymidine kinase
  
  • Convert to acyclo GMP –> aGTP –> DNA –> terminate DNA synthesis in infected cell
• Chicken Pox and Herpes

Question 19

Ribonucleases/Deoxyribonucleases Function

Answer 19

Convert RNA/DNA to short oligomers

Question 20

Phosphodiesterases Function

Answer 20

Convert short oligomers to nucleotides or deoxynucleotides

Question 21

Nucleotidases Function

Answer 21

Convert to nucleosides/deoxynucleosides

Question 22

Nucleosidases Funcations

Answer 22

Removes ribose group to form Pyrimidines / Purines Rings

Question 23

Purine Nucelotide Catabolism: GMP

Oxidative Process

Answer 23

GMP –> Guanosine –> Guanine –> Xanthine –> Uric Acid (via xanthine oxidase)

Question 24

Purine Nucelotide Catabolism: AMP

Oxidative Process

Allopurinol inhibits what enzyme? What steps does this affect?

Answer 24

AMP –> IMP –> Inosine

AMP –> Adenosine –> Inosine (Adenosine Deaminase (ADA)) –> Hypoxanthine –> Xanthine (Xanthine Oxidase) –> Uric Acid (Xanthine Oxidase)

Xanthine Oxidase inhibited by Allopurinol

Question 25

Adenosine Deaminase (ADA) is involved with what? What do overproductions and deficiencies cause?

Answer 25

* Involved with Adenosine homeostasis * Overproduction ADA: Hemolytic anema (increased adenosine degradation --\> premature RBC destruction) * Underproduction ADA: second most common form of severe combined immunodeficiency (SCID).

Question 26

What is GOUT Where is it mostly affected?

Answer 26

Intense pain and inflammation in joints Big toe most affected (metatarsal pharangeal joint)

Question 27

When do MSU (Monosodium Urate) crystals precipitate in joints? Why does GOUT occur in extremities more often

Answer 27

When there is high concentration and at low temperatures Lower temperature away from core

Question 28

Pyrimidine Nucelotide Catabolism Cytosine/Uracil What is the fate of the final product?

Answer 28

UTP/CTP --\> Uridine --\> Uracil --\> B-alanine --\> Maonyl CoA (water soluble) FA Synthesis

Question 29

Pyrimidine Nucleotide Catabolism Thymine What does B-aminoisobutyrate indicate? What is the fate of the final products?

Answer 29

Thymine --\> B-aminoisobutryate (estimates DNA turnover) --\> Methmalonyl CoA & Succinyl CoA (water soluble) TCA Cycle

Question 30

Purine Nucelotide Salvage Pathway Adenine --\> AMP

Answer 30

Adenine + PRPP --\> AMP via **adenine phosphoribosyl transferase (APRT)** **Renal Lithiasis (kidney stone)** occurs with APRT defect

Question 31

Purine Nucleotide Salvage Pathway Guanine/Hypoxanthine --\> GMP/IMP What is caused by this defective enzyme?

Answer 31

Guanine/Hpoxanthine + PRPP --\> GMP / IMP (Hyoxanthine guanine phosphoribosyl transferase **(HGPRT)** Lesch-Nyhan Syndrome & Kelly Seegmiller Syndrome occur with HGPRT defect

Question 32

Lesch Nyhan Syndrome What does this cause?

Answer 32

Defect in HGPRT enzyme in purine salvage pathway Overproduce uric acid --\> Primary hyperuricemia and hyperuricosuria (leading to gout) Urate kidney stones

Question 33

Pyrimidine Nucelotide Salvage Pathway

Answer 33

Uracil + Ribose --\> Uridine --\> UMP --\> UDP --\> UTP Thymin + deoxyribose --\> Deoxythymidine --\> dTMP (thymidine kinase - acyclovir)--\> dTDP --\> dTTP