Nucleotides Pyr

Question 1

Pyrimidine Ingredients

Answer 1

Gln, Asp, CO2, ATP, PRPP, FAD

Question 2

Pyrimidine Synth step 1

Answer 2

Make carbomyl phosphate
Gln, CO2, ATP used
Enz = CPS 2 (same as CPS 1 but not in mito)
Rqrs PRPP inhib by UTP

Question 3

Pyrimidine Synth step 2-4

Answer 3

Make orotic acid

From addition of Asp to Carbomyl phosphate, makes body of pyr

Question 4

Pyrimidine Synth step 5-6

Answer 4

Finish body
Orotate binds PRPP to OMP to UMP
enz = UMP synthase

Question 5

Pyrimidine Synth step 7

Answer 5

UMP to UDP

rqrs ATP, UDP to UTP or dUDP therefore number of P added determines UDP outcome

Question 6

Pyrimidine Synth step 8a

Answer 6

UDP to CTP/dCTP
UDP to UTP to CTP (rqrs Gln)
CTP minus P (ribonucleotide reductase) to dCTP

Question 7

Pyrimidine Synth step 8b

Answer 7

UDP to dUDP
enz = ribonucleotide reductase which reduces ribose sugar and is used for all DNA
act by ribonucleotides and inhib by deoxyribonucleotides (enough DNA)
Rqrs Thioredoxin and NADPH; irreversible

Question 8

Pyrimidine Synth step 8c

Answer 8

dTDP
UDP to dUDP (ribonuc reductase) to dUTP (add P) to dUMP (minus PP) to dTMP (add CH3, via thymidylate synthase, rqrs THF-Me)

Question 9

Pyrimidine Degrade

Answer 9

Degraded to soluble molecules which are converted to acetyl CoA, Succinyl CoA
No salvage pathway

Question 10

Orotic Aciduria

Answer 10

Mut in subunits of UMP synthase; Orotate phosphoribosyl transferase or OMP decarboxylase
leads to poor growth, megoblastic anemia, orotic aciduria
Treatment is admin of uridine to improve anemia and decrease excretion of orotic acid as it inhibs CPS2

Question 11

Xeroderma Pigmentosa

Answer 11

AR

Pyr dimerization due to UV dmg, no nucleotide excision repair

Question 12

Methylated Cytosines

Answer 12

When cytosines are methylated by SAM, they can spont deaminate to Thymine
Screws up DNA sequence

Question 13

5-Fluorouracil

Answer 13

Prevents dUMP methylation therefore inhib thymine buildup