Exam 3 Nucleotide Metabolism (DNA) Flashcards
dNTPs synthesis overview:
take any rNDP, reduce it (ie removed -OH) to make dNDPs then add phosphate to made dNTPs
what is the enzyme that will reduce ribose into deoxyribose
ribonucleotide reductase
how does ribonucleotide reductase perform redox rxn
creates free radicals eg catalytic Tyr free radical
why is ribonucleotide reductase not picky
this one enzyme acts on all NDPs and can act on NTPs
NADPH provides
the necessary e-s for redox rxns
ribonucleotide reductase makes
dNDPs
how many regulation sites are on ribonucleotide reductase
3; 1 catalytic site and 2 allosteric sites
what promotes function in allosteric site in ribonucleotide reductase
ATP
what turns off function in allosteric site in ribonucleotide reductase
dATP
the allosteric site preference for activity is called what in ribonucleotide reductase
specificity site; it is a volume dial ie regulates exact amount of activity
what do kinases do in deoxyribonucleotide synthesis
all the dNDPs are converted to dNTPs
why is dTTP special
it makes a detour in making dTTP from UDP
what are the ways to make dUMP for dTTP synthesis
- remove PPi (pyrophosphate) from dUTP
2. deamination of dCMP
to make T (thymine) in deoxy, need extra _ group
methyl
what adds a methyl to dUMP to create dTMP
thymidylate synthase
what is the methyl donor in dTMP synthesis
B9/methyl-THF
what is the clinical relevance of 5-FU?
it makes an unusable substrate for thymidylate synthase (it is a suicide inhibitor) which stops T pathway synthesis
how do we regenerate THF?
NADPH used for reduction of dihydrofolate (DHF)
what do the two drugs that competitively inhibits dihydrofolate reductase accomplish? drug names are methotrexate and trimethoprim
inhibit ability to incorporate T in DNA (good for cancer)
how does endonucleases work
“inside” cut in the middle
how does exonucleases work
“outside” chew from the end
endonucleases make
oligonucleotides
exonucleases make
nucleoside monophosphates; NMPs (mononucleotides)
pyrmidines use _ and _ to interconvert between nucleobases and NMPs in 2 steps
phosphorylases and kinases
have nucleoside but use phosphorylase, what are we making
removing sugar so making nucleobases from nucleosides (breakdown pathway)
have nucleoside but use kinases, what are we making
adding a phosphate; makes NMPs ie convert nucleosides into nucleotides (salvage pathway)
nucleotidases work to remove
phosphate to make nucleosides from nucleotides
thymidine kinase 1 works to
make thymidine (nucleoside) into dTMP (nucleotide)
why is viral thymidine kinase not as discriminating as human thymidine kinase, and what is the benefit of this?
viral thymidine will accept purines as well as T’s. The benefit is that make a drug (acyclovir) will not interact with human thymidine kinase so it will terminate synthesis of T’s in viral DNA
purines use _ to interconvert between nucleobases and NMPs in one step
phosphoribosyltransferases
phosphoribosyltransferases do what?
remove phosphate (interchange between nucleobases and NMPs)
adenine phosphoribosyltransferases makes:
AMP
HGPRT makes:
IMP/GMP
hypoxanthine is the precursor for
IMP (purines)
nitrogenous bases can be broken down into (2)
- uric acid
2. B-ureidopropionic acid
uric acid is the final product of
purine catabolismm
B-ureidopropionic acid is the final product of
pyrmidine catabolism
uric acid like glutathione is an _
antioxidant
T/F: uric acid/urate is soluble
FALSE insoluble
how does gout occur?
uric acid crystals collecting in joints
what is one pathology for gout
HPRT deficiency; cannot salvage nucleobases of purines
how does SCID occur?
deficiency of adenosine deaminase; breakdown is not functional. dAMP into dATP is inhibited and dAMP accumulates. Inhibition of ribonucleotide reductase so foward rxn and thus no DNA synthesis
