Biochem - Nucleotide Synthesis & Degradation

Front 1

cells that need nucleotides

Back 1

Frequently dividing cells
- Embryos/Fetuses
- Bone marrow, immune cells, GI tract
- Cancer

Front 2

Phosphoribosyl-pyrophosphate (PRPP)

Back 2

Component of purines, pyrmidines, and salvage pathway

Front 3

Purine biosynthesis overview

Back 3

Built on PRPP from the start
- Elements of purine gradually added
- IMP -> either AMP or GMP

Front 4

Purine components

Back 4

- Glycine
- 2 Glutamine aminos
- Aspartate amino
- 2C's from N10-formyl THF
- 1 CO2

Front 5

PRPP to IMP pathway committed step

Back 5

PRPP + Glutamine -> Phosphoribosylamine + Glutamate

Front 6

PRPP committed step enzyme

Back 6

PRPP-Gln-amido transferase

Front 7

PRPP to IMP rxns

Back 7

PRPP + Glutamine -> Phosphoribosylamine + Glutamate
+ 1C
+ Glutamine amino
+ Co2
+ Aspartate amino
+ 1C
= IMP

Front 8

IMP destiny

Back 8

Converted to either AMP or GMP

Front 9

Excess PRPP feedback

Back 9

Activates own committed step

Front 10

Excess IMP, AMP, GMP feedback

Back 10

Inhibits PRPP comitted step

Front 11

Excess AMP/GMP feedback

Back 11

Inhibits IMP -> AMP/GMP

Front 12

Pyrimidine biosynthesis overview

Back 12

Pyrimidine ring built first
- Ring then added to PRPP
- 1C THF addition only for Thymidylate (NOT for C or U)

Front 13

Pyrimidine components

Back 13

Glutamine amide
- Aspartate
- CO2

Front 14

Pyrimidine synthesis rxns

Back 14

Glutatmine + ATP + CO2 (via CPS II) -> Carbomoyl phosphate
-> Dihydroorotate (ring)
-> Orotate + PRPP -> OMP -> UMP + CO2

Front 15

CPS I vs CPS II

Back 15

CPS I = Urea cycle, only in mitochondria
CPS II = in cytosol, only making nucleotides
- Regulation - Spatially separated

Front 16

CTP synthesis

Back 16

UMP phos. 2x -> UTP
UTP + ATP + Glutamine -> CTP + Glutamate

Front 17

Excess CTP feedback

Back 17

inhibits initial step (CPS II)
- also inhibits UTP -> CTP

Front 18

Excess UMP feedback

Back 18

inhibits OMP conversion

Front 19

Excess PRPP/ATP

Back 19

Activate first step

Front 20

TMP synthesis rxns

Back 20

UMP -> dUMP (via Ribonucleotide reductase)
dUMP + N5,10-methylene THF -> TMP + DHF

Front 21

5-Fluorouracil (5-FU)

Back 21

Gets incorporated in pyrimidine nucleotide
- Make 5-FUMP instead of UMP
- 5-FUMP -> 5-FdUMP = inhibits TMP synthesis!

Front 22

5-FU drug mode of action

Back 22

Mimics pyrimidine
- acts like dUMP, product falls apart
- no production of TMP (DNA synthesis problems)

Front 23

Methotrexate drug effects

Back 23

Inhibits DHFR
- Reduced DHF, THF production
- Reduced nucleotide (A,G,T) production

Front 24

Hydroxyurea

Back 24

Inhibits Ribonucleotide reductase
- Reduced DNA nucleotides

Front 25

Gemcitabine

Back 25

Potent cancer drug
- Halts DNA synthesis
- Also irreversibly binds ribonucleotide reductase

Front 26

Purine/pyrimidine analog functions

Back 26

1) Chemo drugs - inhibit DNA synthesis by impersonating nucleotides
2) Immunosuppressive (impair lymphocyte production)
3) Anti-biotics/virals - mess up nucleotide metabolism in microbes

Front 27

Nucleoside vs. Nucleotide

Back 27

Nucleotides have one or more phosphate groups, nucleosides have none

Front 28

Chemo drugs

Back 28

Fluorouracil
- Methotrexate
- Hydroxyurea
- Gemcitabine

Front 29

Anti-herpes drugs

Back 29

Activated by Herpes own Thymidine kinase (tk) = Only affect infected cells
- Inhibit herpes DNA polymerase
- Acyclovir
- Ganciclovir
- Famciclovir

Front 30

Anti-retroviral drugs

Back 30

Activated by cellular kinases
- Inhibit reverse transcriptase because they lack 3' -OH groups
- Chain terminators

Front 31

AZT, DDI, and DDC

Back 31

no -OH groups
- Chain terminators

Front 32

Leflunomide

Back 32

Rheumatoid arthritis drug
- Inhibits ribonucleotide production in lymphcytes
- Immunosuppressive

Front 33

Azathioprine

Back 33

Immunosuppressive drug
- Used after organ transplants
- Prodrug of Mercaptopurine - inhibits DNA synthesis
- Affects proliferating cells (B- and T- cells)

Front 34

Nucleoside analog risks

Back 34

Hepatitis B, liver failure
- Inhibition/mutation of mitochondrial DNA

Front 35

Mitochondrial toxicity syndrome

Back 35

-Lactic acidosis (lacate metab. problems)
- Fatty liver (can't oxidize FA)
- Hypoglycemia (gluconeogenesis steps affected)
- Mm. weakness - inadequate energy made

Front 36

Adenosine nucleotide breakdown pathway

Back 36

Adenosine nucleotides -> Inosine -> Hypoxanthine -> Xanthine -> Uric acid

Front 37

Guanine nucleotide breakdown pathways

Back 37

Guanine nucleotides -> Guanosine -> Guanine -> Xanthine -> Uric acid

Front 38

Purine salvage pathways

Back 38

1) Guanine -> GMP (via PRPP and HGPRT)
2) Hypoxanthine -> IMP (via PRPP and HGPRT)

Front 39

HGPRT

Back 39

Hypoxanthine-guanine phosphoribosyl transferase

Front 40

Uric acid

Back 40

True metabolic "dead end"
- High concentration - can precipitate in joints, skin, or urine

Front 41

Hyperuricemia causes

Back 41

- Too much purine synthesis (excess PRPP or crazy enzymes)
- HGPRT salvage failure (Lesch-Neyhan)
- Reduced renal clearance - competing drugs, anions
- High DNA/RNA release from dying tumor cells

Front 42

Uric acid deposits

Back 42

- Gout - in joints
- Tophi - in CT (ears)
- Kidney stones

Front 43

Home distilling hyperuricemia

Back 43

Pb in sauter
- Lead poisoning - impaired uric acid clearance, gout

Front 44

Lesch-Neyhan

Back 44

X-linked recessive HGPRT defect

Front 45

Hyperuricemia treatment

Back 45

- Minor purine dietary restriction
- Xanthine oxidase inhibitors (less hypoxanthine -> xanthine)

Front 46

Allopurinol

Back 46

Xanthine oxidase inhibitor (less hypoxanthine -> xanthine)

Front 47

Adenosine deaminase deficiency (ADA)

Back 47

Accumulate adenosine and deoxyadenosine
- Ribonucleotide reductase inhibited
- Shortage of other dNTP's
- Poor DNA synthesis - impairs lymphocytes
- Immunodeficiency