Question 1

How would the flux of the pyrimidine biosynthetic pathway in E.coli cells be affected if the enzyme level of PRPP synthetase is upregulated? Explain your reasoning.

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Question 2

Contrast the source of the nitrogen required for the conversion of UTP to CTP in humans and bacteria.

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Question 3

An in vitro experiment with all precursors available for the conversion of dUMP to dTMP would also need to include thymidylate synthase and two additional enzymes necessary for the regeneration of N⁵,N¹⁰-methylenetetrahydrofolate.What are the two enzymes?

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Question 4

What is the name of the enzyme that catalyzes the methylation of dUMP to generate dTMP? Describe the mechanism of the enzyme and include the coenzyme requirement.

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Question 5

Mutations in HGPRT cause Lesch-Nyhan syndrome.Mutations can lead to two different outcomes,both of which result in a reduction of guanine salvaging in cells.Contrast the two classes of mutations in HGPRT that can lead to the same result.

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Question 6

Describe how feedback inhibition by GDP may affect the flux of the ATP synthesis pathway.

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Question 7

A part of the pathway of UMP biosynthesis is shown below.What intermediate is missing? What is the enzyme that generates this compound in the pathway? What is the enzyme that uses this compound as a substrate in the pathway?
Carbamoyl phosphate + Aspartate  Carbamoyl aspartate __________  Orotate

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Question 8

The oxidation of dihydroorotate to orotate,which occurs during the biosynthesis of UMP,uses what molecule as an electron acceptor?

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Question 9

Distinguish between the enzyme requirements for the regeneration of NADP⁺ needed during dNDP formation in humans and bacteria.

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Question 10

Two biosynthesis steps are necessary to incorporate the carbon from HCO₃ into carbamoyl aspartate.Describe the intermediate compound generated during this conversion.

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Question 11

Identify the error in the diagram of the regulation of flux through the pyrimidine biosynthetic pathway shown below.

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Question 12

What is the name of the compound below,which is part of the pathway that regenerates N⁵,N¹⁰-methylenetetrahydrofolate?

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Question 13

Glutamine-PRPP amidotransferase is a tetrameric enzyme that displays sigmoidal kinetics when no inhibitors are present.In the presence of either GTP or ATP the kinetics curve is sigmoidal.Why does this difference in kinetics occur?

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Question 14

The activity site of ribonucleotide reductase can bind two different molecules,whereas the specificity site can bind several.Construct a situation where the activity of the enzyme is inhibited by choosing the identity of the molecules bound to each site.

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Question 15

Compare the regulatory effects of ATP and CTP on ATCase in E.coli.

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Question 16

What would be the effect on the enzyme activity of a mutant ribonucleotide reductases in which the metal-coordinated Tyr is missing? Explain your reasoning in the context of the role of the Tyr in the mechanism of the enzyme.

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Question 17

Propose a pathway by which AMP could be converted to hypoxanthine in a cell if there is a mutation that inactivated the enzyme AMP deaminase.

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Question 18

What would be the effect on thymidylate synthase activity if raltitrexed is present?

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Quiz 18: Nucleotide Metabolism