What intermediate or intermediates in purine synthesis would you expect to accumulate in sulfanilamide-treated bacteria?
1. glycinamide ribonucleotide and 5-aminoimidzole-4-carboxamide
2. 4-Carboxy-5-aminoimidazole ribonucleotide and 5-phosphoribosylamine
glycinamide ribonucleotide and 5-aminoimidzole-4-carboxamide
Suppose that a cultured mammalian cell line was treated with sulfanilamide. What intermediates might accumulate in these cells?
1.glycinamide ribonucleotide and 5-aminoimidazole-4-carboxamide ribonucleotide
2. 5-aminoimidazole ribonucleotide and N-succiny
Mammalian cells are not influenced by sulfanilamide, therefore no products will accumulate.
If you were to determine whether a similar reaction converts adenine directly to dAMP, what metabolite would you need to find in cells at appreciable concentrations
1. 3-Phospho-2'-deoxyribosyl-1-pyrophosphate
2 .5-Phospho-2'-deoxyribosyl-3-pyrophosphate
5-Phospho-2'-deoxyribosyl-1-pyrophosphate
Which of the following enzymes is NOT primarily used in salvage of nucleic acids because the pyrophosphate product is rapidly hydrolyzed?
1. Phosphoribosyltransferase
2. Phosphodiesterase
3. Endonuclease
4.Nucleotidase
5. None of the above
Phosphoribosyltransferase
5-phosphoribosyl-?-D-1-pyrophosphate is a key intermediate in de novo synthesis of nucleotides but not in salvage pathways.
True
False
FALSE
Which of the following compounds is NOT a precursor for nucleotide biosynthesis?
Carbamoyl phosphate
Glutamine
Glycine
Fumarate
Aspartate
Fumarate
Choose the most plausible mechanism by which DON inhibits these enzymes.
1. DON interacts with hydrophobic amino acid side chains inside protein molecules because of its amphiphilic properties. This destabilizes the structure of the enzymes depriving them
The diazomethyl group on carbon no. 5 in this glutamine analog is reactive and is thought to alkylate the position in the enzyme that becomes amidated by glutamine amidotransferase reactions. This irreversibly blocks access to the site by glutamine.
Which participants in pyrimidine synthesis?
Select all that apply.
UTP
dihydroorotate
OMP
orotate
carbamoyl aspartate
UTP
Which intermediate or intermediates in purine nucleotide biosynthesis would you expect to accumulate in DON-treated cells?
Select all that apply.
PRPP
formylglycinamide ribonucleotide
5-phosphoribosylamine
formylglycinamidine ribonucleotide
XMP
IMP
glycin
PRPP, XMP, Fomylglycinamide
The purinosome contains enzymes that convert the serine hydroxymethyl group to the formyl group of 10-formyltetrahydrofolate.
1)Serine+THF?Glycine+5,10?methylene?THF+H2O
2) 5,10?METHYLENE-THF+NAD(P).?5,10?methenyl?THF+NAD(P)H+H+
3) 5,10?methenyl?THF+H2
O?10?formyl?THF
Consider either the purinosome or a multifunctional protein such as the CAD protein. Choose the evidence showing that the enzyme "channels" substrates through a multistep reaction sequence.
Select all that apply
1. The whole pathway would be immediately i
3,4,5
What additional pathway exists for GTP synthesis?
1. G-proteins produce GTP from GDP.
2. In some bacteria GTP is produced during fermentation instead of ATP.
3.The succinyl-CoA synthetase reaction in the citric acid cycle synthesizes GTP from GDP.
4. The
3.The succinyl-CoA synthetase reaction in the citric acid cycle synthesizes GTP from GDP.
Which of the following statements about purine biosynthesis in vertebrates is FALSE?
1. The multienzyme complex is called a purinosome.
2. Six proteins form a multienzyme complex with covalent linkages.
3.Many of the proteins are multifunctional in that t
Six proteins form a multienzyme complex with covalent linkages
The initial end products of purine nucleotide biosynthesis are monophosphates.
True
False
TRUE
The text describes a form of gout that results from HGPRT deficiency. Which enzyme abnormalities might similarly lead to hyperuricemia?
Select all that apply.
1.mutations that lead to overexpression of PRPP synthetase
2.mutations that weaken allosteric re
1,3,4
Why might this treatment be effective, while injection of the missing enzyme is ineffective in other conditions, such as HGPRT deficiency or a deficiency of one of the mitochondrial deoxyribonucleoside kinases?
Injected adenosine deaminase need not be taken up into cells in order to be effective because the substrates, adenosine and deoxyadenosine, are uncharged and, when they accumulate, can efflux from cells and undergo deamination in the extracellular space a
Nucleoside phosphorylase cleaves a glycosidic bond to yield a base and either ribose-1-phosphate or deoxyribose-1-phosphate.
True
False
TRUE
The end product of purine catabolism in humans is:
allantoin.
xanthine.
uric acid.
hypoxanthine.
urea.
uric acid
CTP synthetase is allosterically activated by GTP.
What function might this play in the cell?
1. This is a way to prevent GTP overproduction, because CTP, in its turn, is an allosteric inhibitor of purinosome enzymes E1 and E3 involve d in produxtion of G
This is a way to keep purine and pyrimidine nucleotide pools in balance
Why do mutant cells have unbalanced nucleotide pools and require thymidine in growth medium?
1.Uncontrolled conversion of UTP to CTP elevates pools of cytidine nucleotides leading to unbalanced pyrimidine nucleotide composition associated with toxic effec
Uncontrolled conversion of UTP to CTP elevates pools of cytidine and deoxycytidine nucleotides, while pools of uridine and thymidine nucleotide pools are diminished. The depletion of endogenous thymidine nucleotides explains the growth requirement for exo
Why do mutant cells have an elevated spontaneous mutation rate?
1. The perturbed dNTP pool imbalance (dCTP/dTTP pool ratio is elevated) causes DNA replication errors, principally C incorporated opposite A, that lead to mutations.
2.The diminished level of
The perturbed dNTP pool imbalance (dCTP/dTTP pool ratio is elevated) causes DNA replication errors, principally C incorporated opposite A, that lead to mutations
All six atoms in the pyrimidine ring are derived from two amino acids.
True
False
FALSE
Mammalian cells can become resistant to the lethal action of methotrexate by the selective survival of cells containing increases in dihydrofolate reductase gene copy number so that intracellular levels of the enzyme become very high.
What other biochemic
1,3,5,6,7
A classic way to isolate thymidylate synthase-negative mutants of bacteria is to treat a growing culture with thymidine and trimethoprim. Most of the cells are killed, and the survivors are greatly enriched in thymidylate synthase-negative mutants.
What p
2,5
What is the biochemical rationale for the selection? (That is, why are the mutants not killed under these conditions?)
1.The mutants have negligible flux through the thymidylate synthase reaction because of the enzyme deficiency, they no longer need their
3,5
How would the procedure need to be modified to select mammalian cell mutants defective in thymidylate synthase?
1.Use methotrexate in addition to trimethoprim for the selection, because mammalian cells utilize tetrahydrofolate coenzyme pools more actively
Use methotrexate instead of trimethoprim for the selection, because trimethoprim is an ineffective inhibitor of mammalian dihydrofolate reductases
The text states that a side effect of 5-fluorouracil therapy is its incorporation into RNA.
1.FU+deoxyribose?1?phosphate?Fluorodeoxyuridine(FUdR)Pi (thymidine phosphorylase)
2) Fluorodeoxyuridine+ATP?F?dUMP+ADP
Which statement about nucleotides is FALSE?
1.The only role of deoxyribonucleotides is as constituents of DNA.
2.The electrons for reduction of ribonucleotides to the corresponding deoxyribonucleotides ultimately come from NADPH.
3.dTTP can only be synthe
dTTP can only be synthesized from dCDP
All of the dNTPs are produced in approximately the same amounts because the first step in each pathway is catalyzed by the same ribonucleotide reductase enzyme
T or F
FALSE
The mechanism of action of dihydrofolate reductase inhibitors used for chemotherapy is based on their ability to block the synthesis of dTMP.
True
False
TRUE
5-methyl-dCMP completely substitutes for dCMP
1.virus-specified dCMP demethylase
2.virus-specified dCMP methylase
3.virus-specified dCMP monooxigenase
4.virus-specified dCMP reductase
virus-specified dCMP methylase
5-hydroxymethyl-dUMP completely substitutes for dTMP. Choose a set of virus-coded enzyme activities that could lead to the observed substitution.
virus-specified dUMP hydroxymethyltransferase
virus-specified hydroxymethyl-dUMP kinase
virus-specified 5-hyd
virus-specified dUMP hydroxymethyltransferase
virus-specified hydroxymethyl-dUMP kinase
dUMP completely substitutes for dTMP. Choose a set of virus-coded enzyme activities that could lead to the observed substitution.
Select all that apply.
virus-specified inhibitor of thymidylate synthase
virus-specified dTMP demethylase
virus-specified dUT
virus-specified inhibitor of thymidylate synthase,
Virus- specified dUTPase
Consider the large number of therapeutically effective nucleoside analogs.
Part A
Why do you suppose that these drugs are administered as nucleosides, rather than as nucleotides, which would be more readily converted to the active form of the drug?
Nucleo
Nucleotides, being charged by the presence of phosphate, can be taken up into cells only by specific transport systems, whereas uncharged nucleosides are readily taken up into most cells by facilitated diffusion.
.