Term
| What are some of the major diseases seen with Purine and Pyrimidine Metabolism? |
|
Definition
1) Gout
2) Adenosine deaminase deficiency
3) Lesch-Nyhan syndrome
4) Orotic Aciduria |
|
|
Term
|
Definition
| Accumulation of uric acid which will precipitate in joints and lead to severe pain. It is a direct result of a degradation product of purine rings, from excess purine degradation. Uric acid is relatively insoluble. |
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Term
| What are the functions of a purine or pyrimidine? |
|
Definition
1) energy source
2) precursor for nucleic acid biosynthesis
3) precursor for cofactor synthesis
4) second messenger
5) allosteric regulator
6) methyl donor
7) catalysis |
|
|
Term
| What are the two pathways for purine synthesis? |
|
Definition
1) de novo (from scratch)
2) salvage (take a free base and create a nucleotide)- dietary absorption of purines and pyrimidines is low |
|
|
Term
| Most purines are converted to what? And where is this released? |
|
Definition
| uric acid, released in the blood |
|
|
Term
| Why can't hydroxybutyrate be used to synthesize ribose for purine synthesis? |
|
Definition
| It is a ketone body, we can't get net carbon from anything that is ketogenic. |
|
|
Term
| What is a key intermediate for purine biosynthesis, pyrimidine biosynthesis, NADH synthesis, and salvage pathways for purines and pyrimidines? |
|
Definition
|
|
Term
| What enzyme makes PRPP from ribose-5-phosphate? |
|
Definition
|
|
Term
What activates PRPP synthetase?
What inhibits PRPP synthetase? |
|
Definition
activators- Pi
inhibitors- ADP and GDP |
|
|
Term
| Is PRPP the first committed step of purine biosynthesis? |
|
Definition
| No, its purpose is to activate C-1 of ribose for the next step |
|
|
Term
| What is the committed step of purine biosynthesis? |
|
Definition
| Transfer of Gln amide to C-1"with loss of pyrophosphate |
|
|
Term
| What inhibits the committed step of purine biosynthesis? |
|
Definition
AMP and GMP (enzyme binds to adenine or guanine, so technically A-DP/TP or G-DP/TP can also inhibit)
Inhibition additive: need both purines to totally inhibit enzyme |
|
|
Term
| Whenever aspartate donates its N, what results? |
|
Definition
|
|
Term
| Which disorder will lead to an increase in PRPP levels? |
|
Definition
| Von Gierke's disease- loss of glucose-6-phosphatase (Glycogen Storage DisorderI) |
|
|
Term
| Which ring is formed first in purine biosynthesis? |
|
Definition
|
|
Term
| Which purine is formed first? |
|
Definition
|
|
Term
| What enzyme is needed for the committed step? |
|
Definition
| Amidophosphoribosyl transferase |
|
|
Term
| What are the sources of all the base components of purines? |
|
Definition
1) glutamine provides 2 N (requires two glutamines)
2) glycine(provides N-C-C)
3) CO2
4) Aspartate- provides N
5) N10-Formyl-THF 2 of them provide 2 total C's |
|
|
Term
| Where does the -NH2 come from in AMP? |
|
Definition
| It comes from aspartate to fumarate |
|
|
Term
| What two enzymes are needed for AMP biosynthesis from IMP? What else is needed? |
|
Definition
1) Adenylosuccinate Synthetase (needs Aspartate and GTP)
2) Adenylosuccinate (Fumarate leaves) |
|
|
Term
| What regulates Adenylosuccinate Synthetase? |
|
Definition
|
|
Term
| Where does the -NH2 comes from in GMP biosynthesis? |
|
Definition
| Glutamine( -NH2 goes to position 2) |
|
|
Term
| What enzymes are needed for GMP biosynthesis from IMP? |
|
Definition
1) IMP DH (make NADH)
2) GMP synthetase (need Glutamine and ATP) |
|
|
Term
|
Definition
|
|
Term
| What enzyme makes GDP from GMP and where does the Pi come from? |
|
Definition
-GMP kinase
-ATP is the phosphate donor |
|
|
Term
| What enzyme makes ADP from AMP and where does the Pi come from? |
|
Definition
-adenylate kinase (myokinase in the muscle)
-ATP is the phosphate donor |
|
|
Term
| What produces a nucleotide triphosphate? |
|
Definition
| nucleoside diphosphate kinases (switches Pi from one NTP to a different NDP) |
|
|
Term
| Overproduction of purines leads to? |
|
Definition
Increased degradation of purines
Increased uric acid
Possibly Gout |
|
|
Term
| What can lead to overproduction of purines? |
|
Definition
1) high levels of glutamine
2) high PRPP levels
3) increased activity of amdiophosphoribosyl-transferase
4) loss of negative effectors for amdiophosphoribosyl-transferase(this can be loss of A or G site) |
|
|
Term
| Is the Km of amidophosphoribosyl-transferase for Gln or PRPP higher or lower than normal cellular concentrations? |
|
Definition
| Its higher, so an increase in Gln or PRPP will just increase rate of production of purines |
|
|
Term
| What cells need the salvage pathway? |
|
Definition
| erythrocytes and leukocytes(lack de novo pathway) |
|
|
Term
| What cells need the salvage pathway? |
|
Definition
| erythrocytes and leukocytes(lack de novo pathway) |
|
|
Term
| What is the major site of base synthesis? |
|
Definition
| liver- sends bases to other tissue for salvage |
|
|
Term
| Purine nucleoside phosphorylase(PNP) deficiency leads to? |
|
Definition
Immune disorders
-T-cell deficiency
-Hypouricemia |
|
|
Term
| Why does a PNP deficiency lead to an immune disorder? |
|
Definition
| dGTP accumulates (cannot be degraded), which leads to a reduced production of dCTP (will learn shortly), which leads to reduced levels of DNA synthesis- high levels of dGTP will reduce the activity of Ribonucleotide reductase in making dCTP |
|
|
Term
| Lesch-Nyhan deficiency results from and causes what? |
|
Definition
-HGPRT defieincy <2% activity
Symptoms include- neurological defects, self-mutilation, and gout |
|
|
Term
| If there is an HGPRT deficiency and 2-10% of the activity is observed what symptoms are observed? |
|
Definition
|
|
Term
| What results from Adenosine Deaminase Deficiency? |
|
Definition
-SCID(severe combined immunodeficiency disease)
Pt lacks B and T cells and lacks thymus
Treay with gene therapy |
|
|
Term
| How does SCID result from Adenosine Deaminase Deficiency? |
|
Definition
dATP levels increase- this is an inhibitor for ribonucleotide reductase, blocking DNA synthesis
-affects lymphocytes which must proliferate in response to antigens, so lose immune function |
|
|
Term
| What occurs primarily in the muscle and brain? It produces ammonia to buffer lactic acid? |
|
Definition
|
|
Term
| What causes this cycle to begin? |
|
Definition
| increase in levels during exercise |
|
|
Term
| Where does the nitrogen come from in the Purine Nucleotide cycle? |
|
Definition
| It comes from Aspartate which was made from a BCAA, Asp donates the NH3 to IMP and Fumarate is made |
|
|
Term
| What is the most important enzyme in purine degradation and the target for many drugs? |
|
Definition
|
|
Term
| What are some treatments for Gout? |
|
Definition
1) Reduce purine uptake through dietary means
-Partially effective, recall intestinal cells convert purines to uric acid
-most purines come from de novo pathway
2) Promote uric acid secretion by the kidney
-drugs do this
-does not solve problem, still excess uric acid and gout attacks still can occur
3) Add enzyme to degrade uric acid further (Uricase does this, but it comes from chimps and is targeted by our immune system, still developing less antigenic version)
4) Inhibit uric acid production with drugs (Allopurinol) |
|
|
Term
| Uricase breaks uric acid into? |
|
Definition
| Allantoin- which is more water soluble |
|
|
Term
| How does Allopurinol work in treatment of Gout? |
|
Definition
It irreversibly binds to Xanthine oxidase creating oxypurinol-that remains bound to xanthine oxidase. This is a suicide inhibitor.
There is a buildup of xanthine and hypoxanthine, but this is more water soluble than uric acid and it is readily cleared from circulation by the kidneys |
|
|
Term
| What is a difference between purine and pyrimidine synthesis? |
|
Definition
| In pyrimidines, ribose is added after bas formation. Opposite of purines. |
|
|
Term
| What is required for both purine and pyrimidine biosynthesis? |
|
Definition
1) PRPP
2) Gln
3) CO2
4) Aspartate |
|
|
Term
| What is needed to make the pyrimidine base? |
|
Definition
1) Glutamine
2) CO2
3) Aspartate
4 or 1/2) Carbamoyl Phosphate |
|
|
Term
| What is the major regulated step in pyrimidine biosynthesis? |
|
Definition
|
|
Term
| What is the difference between CPS-I and CPS-II? |
|
Definition
CPS-I located in the mitochondria and fixes free NH3
CPS-II located in cytoplasm and does not fix free NH3 |
|
|
Term
|
Definition
| It takes CO2 + Gln + ATP -> Carbamoyl Phosphate |
|
|
Term
What activates CPS-II?
What inhibits CPS-II? |
|
Definition
activator-PRPP
inhibitor-UTP |
|
|
Term
| UMP synthase contains what? |
|
Definition
| Both Orotate Phosphoribosyl Transferase and Orotidylic Acid Decarboxylase |
|
|
Term
|
Definition
| CPS-II, Aspartate transcarbamoylase and Dihydro-orotase |
|
|
Term
| What is the first pyrimidine formed in nucleic acids? |
|
Definition
|
|
Term
|
Definition
| UTP so UMP needs to be made into UTP for CTP to be made use a UMP kinase then a UDP kinase |
|
|
Term
| What makes CTP from UTP? What is the nitrogen donor and what ring number is it added to? |
|
Definition
-CTP Synthetase (uses ATP and H2O)
-Glutamine provides the -NH2
-It's added to C-4' |
|
|
Term
| The UTP to CTP rxn is similar to what other rxn? |
|
Definition
| XMP to GMP(both use Gln as source of -NH2) |
|
|
Term
| What enzyme makes all deoxyribonucleotides from XDP's to make dXDP's? |
|
Definition
|
|
Term
| When making deoxynucletotide, ribose is ___________ and thioredoxin is________. What happens to make it ready for another rxn? |
|
Definition
ribose is reduced
thioredoxin is oxidized
to regain thioreduxin it is reduced by NADPH |
|
|
Term
| Ribonucleotide reductase contains how many allosteric sites? |
|
Definition
-Overall activity site(activates ort inhibits enzyme)
-Substrate specificity site(controls which substrate to reduce) |
|
|
Term
| Ribonucleotide reductase binds two ligans which are they? |
|
Definition
-ATP activates enzyme
-dATP inactivates enzyme
(they both bind to the same site, compete for binding) |
|
|
Term
| When dTMP is synthesized from dUMP, where does the methyl group come from and what member of the ring gets this methyl? |
|
Definition
| The methyl comes from THF, it is added to C-5' |
|
|
Term
| What enzyme is the only one where THF is oxidized to dihyrofolate? |
|
Definition
|
|
Term
| What is used to regenerate THF? |
|
Definition
| Dihydrofolate reductase (DHFR) |
|
|
Term
| What happens if you inhibit DHFR and what drug does this? |
|
Definition
| Then THF (tetrahydrofolate) cannot be regenerated. This will lead to an inability to produce dTMP, and eventually will stop DNA synthesis. DHFR is a target of anti-cancer drugs such as ***methotrexate |
|
|
Term
| What happens when you have an Adenosine Deaminase deficiency? |
|
Definition
1 )deoxyadenosine levels increase
2) Adenosine kinase will convert deoxyadenosine to dAMP
3) dAMP is converted to dATP
4) As dATP levels increase in lymphocytes, inhibition of ribonucleotide reductase occurs
5) this cause levels of dGTP, dCTP, and dTTP to be too low for DNA synthesis to occur
6) T cells can't proliferate and the individual has an immune deficiency
7) this gets so bad you might as well call it SCID |
|
|
Term
| What is the major enzyme in pyrimidine base salvage? |
|
Definition
| pyrimidine nucleoside phosphorylase- it take free base, and ribose-1-phosphate to produce nucleoside and free phosphate |
|
|
Term
| What base will pyrimidine nucleoside phosphorylase not make? |
|
Definition
| thymine (do to low affinity) |
|
|
Term
| What will take Thymine and deoxyribose-1-phosphate and produce thymidine? |
|
Definition
|
|
Term
| What will phosphorylate uridine or cystidine? |
|
Definition
| Uridine-Cystidine Kinase (uses ATP and makes ADP) |
|
|
Term
| What will phosphorylate thymidine and make dTMP? |
|
Definition
| Thymidine kinase (uses ATP and makes dADP) |
|
|
Term
| What will phosphorylate dC? |
|
Definition
|
|
Term
| Where does pyrimidine catabolism occur? What is different about the end products? |
|
Definition
| It occurs in the liver, but the end products are soluble and no known disorders |
|
|
Term
| Hereditary Orotic Aciduria |
|
Definition
Cause: reduced activity of orotate phosphoribosyl transferase, and orotidine 5'-phosphate decarboxylase
-Pyrimidine de novo pathway is completely blocked
Symptoms: Retarded growth and development
-Hypochromic anemia
-excessive excretion of orotic acid
Treat with uridine or uracil (works well) because CPS-II is inhibited by UTP. |
|
|
Term
| What three nucleotide reactions require a THF derivative? |
|
Definition
-Two steps in the formation of the purine ring utilize N10-formyl-THF
-The conversion of dUMP to dTMP utilizes N5,N10 methylene THF, and produces DHF |
|
|
Term
| What 4 reactions in amino acid metabolism require THF forms? |
|
Definition
1) Serine to glycine reaction generates N5, N10 methylene THF
2) Glycine cleavage enzyme generates N5, N10 methylene THF
3) Histidine degradation generates N5 formimino THF
4) Homocysteine + N5-methyl THF yields methionine |
|
|
Term
| Why is folate needed in the diet? |
|
Definition
| We need it for THF because we can't generate a pteridine ring. Carbons are carried in various states on N5 and N10. |
|
|
Term
|
Definition
| DNA synthesis (purine rings and dTMP) |
|
|
Term
| What are two cancer drugs that block or inhibit DHFR? |
|
Definition
1) aminopterin
2) methotrexate |
|
|
Term
| What is the suicide inhibitor of thymidylate synthase? |
|
Definition
|
|
Term
| What is incorporated into HIV DNA, it is a chain terminator? |
|
Definition
|
|
Term
| What drug inhibits dihydrofolate reductase(DHFR)? |
|
Definition
|
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