Day 21

Question 1

Fate of IMP

Answer 1

IMP is rapidly converted to either AMP or GMP

Question 2

Synthesis of AMP

Answer 2

First IMP is condensed with aspartate by adenylosuccinate synthetase and then fumarate is eliminated by adenylosuccinate forming AMP

Question 3

Synthesis of GMP

Answer 3

IMP is oxidized to XMP by IMP dehydrogenase and then an amide group from glutamine with ATP and GMP synthetase making GMP.

Question 4

B and T lymphocytes

Answer 4

In these immune cells IMP dehydrogenase activity is high forming lots of GMP

Question 5

Mycophenolic Acid

Answer 5

Fungal compound that inhibits IMP dehydrogenase and is used as an immunosuppressant.

Question 6

Nucleoside triphosphates

Answer 6

Nucleotide monophosphates must be converted to these so that nucleic acids can be synthesized.

Question 7

Nuceloside Diphosphates

Answer 7

Made from nucleoside monophosphates by base-specific nucleoside monophosphate kinases

Question 8

Nucleoside Monophosphate Kinases

Answer 8

Do not discriminate between ribose and deoxyribose

Question 9

Adenylate kinase

Answer 9

Catalyzes the reaction AMP + ATP —- 2 ADP

Question 10

Nucleoside Triphosphate Kinase

Answer 10

Enzyme that converts nucleoside diphosphates to triphosphates. Written here as ATP is the phosphoryl donor but it can be any nucleoside triphosphate. GDP+ATP—GTP+ADP

Question 11

Regulation of Purine Nucleotide Biosynthesis

Answer 11

Synthesis of IMP, AMP, and GMP are individually regulated. IMP is regulated at first two steps. Second level of regulation is immediately at the branch point of IMP to AMP or GMP.

Question 12

Regulation of IMP

Answer 12

Ribose phosphate pyrophosphokinase is inhibited by both ADP and GDP. Amidophosphoribosyl transferase is inhibited by adenosine phosphates and guanine phosphates and activated by PRPP