Biochem Of Met, Block 2, # 11 - Nucleotide Metabolism

Front 1

What two pathways exist for the creation of nucleotides?

Back 1

NT's come from

DeNovo synthesis: incorporate old amino acids, ribose-5-phosphate, CO2, and NH3 into totally new nucleotides

Salvage: sugars and bases that were previously separated from nucelotides are re-constituted into functional NT's.

Front 2

Pyrimidine and purine synthesis: what common intermediate(s) do they have in common?

What is the major source of nitrogens for NT synthesis?

How common are NT's in the cytoplasm?

Back 2

phosphoribosyl pyrophosphate (PRPP) is the common intermediate for both pyrimidine and purine synthesis.

Glutamine is the major source of NT's (some purines also use asparagine)

NT's exist at very low concentration (less than 1%), so they can be rate limiting and are a good target for therapeutics.

Front 3

What is the AA precursor for purines and pyramadines?

Back 3

Purines is glycine

pyrimidines is aspartate

Front 4

PRPP synthesis: why is it important and what enzyme does it?

Back 4

phospho ribosyl pyrophosphate synthase turns RIBOSE-5-PHOSPHATE into PRPP. This forms:

5-phospho-beta alpha ribosylamine.

This is required for the creation of NT's, and is the FIRST REGULATED STEP.

Front 5

First steps of purine synthesis: first committed step? What happens afterwards?

Back 5

1st committed step:
Nitrogen donation. Remember that for purines, the nitrogen donor is GLUTAMINE, and later asparagine.

Glutamine donates an NH3 to PRPP via Glutamine-PRPP
amidotransferase.


Next, need to add the AA common to purines: glycine! it's added with ATP

Front 6

In purine synthesis, what donates the amino acid group and what donates nitrogens?

After 10 reactions, what's formed?

Back 6

amino acid group comes from GLYCINE, and amino acids come mostly from GLUTAMINE, but also get one from ASPARTATE.

After ten reactions, make IMP (Inositate)

Front 7

What can IMP become, and how?

Back 7

It turns into AMP or GMP.

To become AMP, going to get donation of a amino group from ASPARTATE

To become GMP, going to get an amino group from GLUTAMINE.

Conversion of IMP to AMP: use adenylosuccinate synthase.

Conversion of IMP to GMP: use IMP dehydrogenase.

Front 8

Purine synthesis: what steps are regulated, and what does the regulation?

Back 8

PrPP synthase is regulated by ADP (this will turn off the synthesis of ALL nucleotides)

Glutamine-PrPP amidotransferase is negatively controlled by IMP, GMP, and AMP.

Adenoylsuccinate Synthase (IMP to AMP enzyme) is turned off by its product, AMP.

IMP dehydrogenase (IMP to GMP) is turned off by its product, GMP.

Front 9

Pyrimidine synthesis: what is the first big step?

Back 9

Start with aspartate, add in carbomyl phosphate, and use the enzyme:
Aspartate transcarbomylase

this forms orotate.

Front 10

Once orotate is formed, then what?

Back 10

Orotate goes to Oratidylate, by combining with PRPP.
This uses the enzyme
Orotate phosphoribosyl transferase.

Front 11

Once you make oratidylate, then what? What can be done with the product?

Back 11

oratidylate goes to UMP via oritidylate decarboxylase.

add 2ATP and make UTP, which you can transaminate to make CTP.

Front 12

What disease states can be present in the creation of UMP?

Back 12

orotic acidurias can come from enzyme deficiencies in:

orotate p-ribosyl transferase
or
oritidyl decarboxylase

Front 13

describe the regulation of pyrimidines:

Back 13

Two enzymes are fed back on, both of which promote the synthesis of pyrimidines:

CPS II (carbomyl phosphate synthetase): note that type I is in the mitochondria and does urea cycle, type II in the cytosol and does pyrimidine biosynthesis.

It's activated by PrPP, deactivated by UMP.

1st enzyme in pyrimidine pathway is also subject to regulation: aspartate transcarbomylase, turned off by CTP.

Front 14

How are RT's turned into dRT's? What happens to the e-'s?

Back 14

need to be reduced, using Ribonucelotide Reductase!

Electrons will end up on NADPH

electrons can go down two pathways: the glutaredoxin and thioredoxin pathways. Associate FADH2 with thioredoxin and and GSSH/GSH with glutaredoxin.

Front 15

Once reduction from rNT's to dNT's has been made, how do you make "T"?

what does this have to do with cancer?

Back 15

dUMP to dTMP, using

thymadilate synthase!
note that this requires TETRAHYDRO FOLATE!!!!

if not enough folate, start encorporating UMP's, which are mutations and bad.

Front 16

Purine biosynthesis: what's up? What disease state should we think of?

Back 16

Purines can be salvaged using

hypoxanthine and the enzyme HGPRT to make IMP, which can go to GMP/AMP as before.

Also, can make AMP using adenine and PrPP with APRT.

Lesch-Nyhan syndrome = no HGPRT, so have to do lots of de novo synthesis. this makes PrPP build up, and uric acid (from degreation of excess purines that can't be salvaged) = gout and eat off fingertips (bad brains). See before age 2

Front 17

pyrimidine salvage: what's up?

Back 17

purine nucleoside phosphorylase, followed by more specific kinases.

Front 18

what do we need to know about purine degredation?

Back 18

uses nucleosidases, deaminases, and xanthine formation.

know: XANTHINE OXIDASE (helps make uric acid) is a target for gout therapy (allopuranol)

also, adenosine deaminase deficiency = lots of dATP, inhibit ribonucleotide reductase = stop other nucleotide making = b-cells don't work = bubble boy.

Front 19

what are some cancer therapies based on this?

Back 19

glutamine amiodotransferase targeter: azaserine and acivicin.

thymadiliate synthase inhibitor: flourouracil

dihydrofolate reductase (stop thymadilitate synthase reaction) = methotrexate and aminopterin

trimethoprim also targets dihydrofolate reductase, but targets bacteria.