Purine Nucleotide Biosynthesis

Front 1

What are the bicyclic, planar, aromatic nitrogenous bases?

Back 1

purines; adenine and guanine

Front 2

What are the cyclic, planar, aromatic nitrogenous bases?

Back 2

pyrimidines; thymine, cytosine, uracil

Front 3

Which bases are different between DNA and RNA?

Back 3

thymine (DNA), and uracil (RNA)

Front 4

What is a nucleoside?

Back 4

a nitrogenous base (A,G, T, C, U) plus a sugar (ribose, deoxyribose)

Front 5

What is a nucleotide?

Back 5

a phosphorylated nucleoside

Front 6

What are the suffixes for purines and pyrimidines?

Back 6

purines: -osine
pyrimidines: -idine

Front 7

What atom is usually associated with negatively charged nucleotides within the cell?

Back 7

Mg2+

Front 8

What is the difference between the prefixes tri- and tris-

Back 8

tri- (phosphates linked to each other)
tris- (phosphates linked to a different carbon)

Front 9

How is adenosine unlike the other nitrogenous bases in function?

Back 9

it is unique in that it functions by itself, without being converted, it is implicated in sleep regulation

Front 10

What are the effects of caffeine?

Back 10

it is a competetive inhibitor of adenosine receptors, promotes wakefulness

Front 11

When are purine synthesis pathways most active?

Back 11

during DNA replication (S-phase of cell cycle)

Front 12

What is the major site of purine synthesis de novo?

Back 12

within the cytosol of the liver

Front 13

What is the rate limiting step in purine and pyrimidine synthesis and what is the enzyme involved?

Back 13

the first step, PRPP synthetase

Front 14

What is the first committed step of purine synthesis and what is the enzyme involved?

Back 14

the second step, glutamine-PRPP-amidotransferase

Front 15

What is the last common intermediate and first recognizable purine nucleotide?

Back 15

IMP (common between adenine and guanine pathways)

Front 16

What is the reaction that PRPP synthetase catalyzes and how is it regulated?

Back 16

transfers a pyrophosphate group from ATP to ribose-5-P to form PRPP (activated sugar), allosterically inhibited by purine and pyrimidine nucleotides

Front 17

What is the reactioin that glutamine-PRPP amidotransferase catalyzes and how is it regulated?

Back 17

replaces the pyrophosphate group with the amide nitrogen of glutamine, PRPP is a positive allosteric activator, purine nucleotides are allosteric inhibitors

Front 18

What are some key points to consider in the mechanism leading to the formation of IMP?

Back 18

7 ATP and 2 N-formyl-tetrahydrofolate are required, tetrahydrofolate is required for all purines plus thymidine, folic acid is required, the base in IMP is hypoxanthine, 7 of 9 steps are catalyzed by multifunctional enzymes

Front 19

What are the synthesis products of the two branches originating from IMP and where is the energy supplied from to produce them?

Back 19

AMP - energy from GTP
GMP - energy from ATP

Front 20

How are AMP and GMP converted to their respective diphosphates and triphosphates?

Back 20

to ADP by adenylate kinase
to GDP by guanylate kinase
to ATP and GTP by nucleoside diphosphate kinases (ATP is P donor)

Front 21

What is the salvage pathway for purine nucleotides, how much energy does it use compared to de novo synthesis, and what is the enzyme involved?

Back 21

recycling of purine bases, uses less energy than de novo synthesis, accounts for 90% of purine bases, uses hypoxanthine-guanine phosphoribosyltransferase (HGPRT)

Front 22

For purines that are not salvaged, how are they degraded?

Back 22

amino acid removed from AMP to form IMP by adenosine deaminase → IMP and GMP → inosine and guanosine →hypoxanthine and guanine → guanine converted to xanthine → xanthine oxidase converts hypoxanthine and xanthine to uric acid

Front 23

What is the final product of purine degradation and what is the enzyme that catalyzes the reaction that creates it?

Back 23

uric acid by xanthine oxidase

Front 24

What is the function of HGPRT?

Back 24

in the salvage pathway, recycles hypoxanthine back to IMP and guanine back to GMP

Front 25

How much energy is produced in purine catabolism?

Back 25

none

Front 26

What will a decrease in purine salvage do to de novo purine sythesis?

Back 26

de novo purine synthesis will increase proportionally to the decrease in salvage (as a result, excreted uric acid is relatively constant)