BIOL302 Class 17

Question 1

nitrogenous bases

Answer 1

• pyrimidine
• purine
• both are weakly basic
• both are flat/planar molecules (useful to form hydrogen bonds between bases & provides a 3D structure)

Question 2

Purines

Answer 2

Adenine & Guanine

Question 3

Pyrimidines

Answer 3

Cytosine, Uracil, Thymine

Question 4

Nucleic Acid Polymers

Answer 4

DNA: ATG
RNA: UGC
5 prime to 3 prime

Question 5

nucleosides are building blocks for numerous biological molecules

Answer 5

examples such as cyclic AMP & cGMP are important signaling molecules

Question 6

NTPS (not just ATP)

Answer 6

Important sources of energy for enzymatic catalysis in metabolism (energizing compounds for chemical transfers)

Question 7

AMP

Answer 7

a structural component of important coenzymes like NAD(P), coenzyme A, and FAD

Question 8

cAMP/cGMP and GTP

Answer 8

are important metabolic regulators and signaling molecules (PKA, G-Proteins, etc)

Question 9

metabolic requirements for nucleotides are met by

Answer 9

1) recycling/salvage pathways
2) dietary intake
3) de novo synthesis from pre-existing metabolites

Question 10

metabolic fates of dietary nitrogenous bases overlaps with salvage pathways of bases during normal “tunover”

Answer 10

• free bases and 5-P-Ribose can be used to rebuild NTPS (salvage pathways)
• Ribose-P can be synthesized from glucose via Pentose Phosphate Pathway
• there is a constant and rapid turn-over of nucleic acids in a cell, so salvage is essential

Question 11

PRPP Kinase

Answer 11

• ADP and GDP are negative regulators (PRPP is the limiting substrate in purine synthesis)
• NOT the commitment step since PRPP has multiple metabolic fates (such as the salvage pathway)

Question 12

where does Ribose-5-Phosphate come from? under what conditions would this sugar become available?

Answer 12

• comes from Pentose Phosphate pathway
• becomes available when there’s a high energy demand & when RNA and DNA need to be made

Question 13

Purine Biosynthesis

Answer 13

• step by step building of the base onto the activated ribose PRPP
• the eventual cyclization yields Inosine monophosphate (IMP) which is the direct precursor to both AMP and GMP

Question 14

committed step for purine biosynthesis

Answer 14

Gln-PRPP Amidotransferase

Question 15

why does it make sense for AMP and GMP to be negative regulators?

Answer 15

They’re the end products **

Question 16

once inosine is made it is converted to GMP and AMP

Answer 16

• if you dont have sufficient AMP you cant make GMP, if you dont have sufficient GMP you cant make AMP

Question 17

what do amino acids provide to nucleotide synthesis?

Answer 17

nitrogens

Question 18

uric acid

Answer 18

anything causing a build up of uric acid concentration in blood or urine past its solubility in these liquids can lead to its precipitation

Question 19

gout

Answer 19

painful accumulation of uric acid crystal needles
- clogs arteries, especially at the joints

Question 20

inhibition of xanthine oxidase by allopurinol

Answer 20

prevents uric acid production and allows for xanthine and hypoxanthine to be excreted instead

Question 21

purine salvage

Answer 21

purines are a major metabolic investment so salvage pathways collect free adenine, hypoxanthine, and guanine bases and convert them back to useful forms (nucleotides) via PRPP

Question 22

HGPRT is essential for the purine salvage pathways

Answer 22

• disruption of the enzyme by heritable mutation causes lesch-nyhan syndrome (a sex-linked trait since HGPRT is on the x)
• results in build up of uric acid –> gouty arthritis, severe mental retardation and/or behavioral abnormalities at worse

Question 23

pyrimidine biosynthesis

Answer 23

• unlike purines, the pyrimidine ring is assembled first, and then added to PRPP as a unit
• initial step uses CPSII to make carbamoyl phosphate; built from HCO3- and amide from glutamine
• end-product regulation targets CPSII
• synthesis is essentially coupling of carbamoyl-P to Aspartate, followed by cyclization and transfer to PRPP

Question 24

Tetrahydrofolate

Answer 24

the methyl carrier for methylation of dUMP by thymidylate synthase

Question 25

folate deficiency

Answer 25

can cause anemia in adults and insufficiency during pregnancy that can lead to birth defects like Spina Bifida (failure to close neural tube)