Purines and Pyrimidines

A rapidly dividing cell will have a greater abundance of which nucleotide?

• Guanine and Adenine because purine synthesis is more important for a developing cell

• Cytosine and Thiamine because pyrimidine synthesis is less taxing and therefore proceed more quickly

• The concentration of pyrimidines and purines will be equal regardless of the conditions

• Purines are critical for DNA replication, so purine concentration will be higher

Which of the following is a nucleotide?

For the previous question why was the correct answer the only nucleotide?

• It was the only answer that consisted of a nucleoside bound to a phosphate group

• All of the other answers were sugars

• All of the other answers were bases

• None of the other answers were biologically important molecules

Which of the following is not a biological function of Nucleotides?

• They are precursors to glycogen and other phosphoglycerides

• Nucleotides exclusively compromise the universal energy currency

• They serve as metabolic regulators and mediate the action of many hormones

• Nucleotides entirely make up three major co-enzymes: NADH, FAD, and CoA

Purine biosynthesis involves which of the following precursors?

• Glycine

• Glutamine

• Aspartate

• carbon dioxide

• Formyltetrahydrofolate

• All of the above are required atom contributors

PRPP (Phosphoribosylpyrophosphate) is the source of the ribose sugar in...

• purine de novo synthesis and purine salvage pathways

• purine de novo synthesis

• purine salvage

• purine and pyrimidine de novo synthesis

Which describes the committed step for purine de novo synthesis?

• Glutamine-PRPP amido-transferase is the active enzyme

• PRPP feeds into the committed step

• Glutamine feeds into the step and becomes glutamate

• All of the above

THF is an enzyme that performs which of the following actions?

• Eliminates an amide group

• Transfers one carbon from N10-Formyl THF to the growing purine precursor

• Allosterically activates HGRPT

• Facilitates a Glutamine dependent nitrogen tranfer

• Facilitates ring closure of the growing purine

The base hypoxanthine is described by which of the following statements?

• Inosinic Acid (IMP) is the nucleoside form of hypoxanthine

• Hypoxanthine is critical only to the conversion of IMP to GMP not IMP to AMP

• Hypoxanthine is reduced to xanthine during the purine synthesis pathway

• The oxidation of hypoxanthine to xanthine is blocked by allpurinol

PRPP impacts which of the following?

• De novo synthesis of purines

• Direct production of IMP through PRPP's reaction with Hypoxanthine

• Direct production of GMP through PRPP's reaction with Guanine

• All of the above are catalyzed by HGPRT and all are true in healthy cells

Which of the following is deficient in Gout?

• HGPRT

• ADA (adenosine deaminase)

• PNP (purine nucleoside phosphorylase)

• You have to be more specific, gout could be the result of numerous enzyme deficiencies

• XO (xanthine oxidase)

Lesch Nyhan Syndrome is caused by a deficiency in which of the following?

• PRPP

• XO (xanthine oxidase)

• ADA (adenosine deaminase)

• HGPRT

• You have to provide more information, Lesch Nyhan Syndrome could be caused by the deficiency of a number of different enzymes

Which is the committed step of Pyrimidine synthesis?

• Aspartate Transcarbamoylase ATCase

• Dihydroorotase

• OPRT

• CTP synthetase

Familial Orotic Aciduria can be treated using which of the following methods?

• There is no curative treatment, simply a management of symptoms

• Delivery of large doses of orally administered uridine to simply bypass the early steps of pyrimidine synthesis

• Delivery of large doses of the missing/deficient orotate phosphoribosyltransferase (OPRT)

• Delivery of fully synthesized pyrimidines for uptake into the cell

Which of the following are made by a two enzyme complex (Thymidylate Synthetase and Dihydrofolate reductase) after ribonucleotide reductase acts on freshly minted purines and pyrimidines?

• dADP

• dGDP

• dCDP

• dUDP

• dTTP

Which of the following enzymes should I know really well?

• Ribosomyl Reductase

• PRPP Synthetase

• Xanthine Oxidase

• Dihydrofolate Reductase

• HGPRT

• Amidophosphoryl Transferase ATase = glutamine PRPP amidotransferase

• I should probably know all of these

Why do we use "De Novo" instead of saying from scratch?

• Because Carl Sagan's famous Apple Pie from scratch comment makes it too awesome to use in any setting other than musing about the universe

• Because De Novo is more descriptive

• To confuse those who are sadly lacking in medical jargon

• Because fancy language is awesome