lecture 11 Flashcards
(48 cards)
two biosynthesis pathways
De novo and Salvage
de novo synthesis
“new” synthesis
precursors for de novo
amino acids, ribose 5P, CO2, NH3
salvage pathway
endproducts made from “scavenged” components
how does the salvage pathway get precursors
Recycling of free bases and nucleosides from nucleic acid breakdown
what does de novo synthesis begin with
5-phosphoribosyl 1-pyrophosphate (PRPP)
what does de novo end with
inosinate (IMP)
biosynthesis of AMP and GMP:
IMP is an important precursor
arm 1 of IMP to AMP
add aspartate and GTP
take out fumerate
make adenylate
arm 2 of IMP to GMP
add H2O and reduce NAD
add amino group of glutamine and use ATP
make GMP
3 major inhibition mechanisms
- ribose phosphate pyrophosphokinase
- glutamine-PRPP amidotransferase
- AMP inhibiting adenylosuccinate synthetase
bacterial carbamoyl phosphate synthetase
3 active sites
substrate channeling
important in limiting substrate/intermediates diffusion
when is substrate channeling critical
if intermediates are unstable
aspartate transcarbamolyase
in charge of bacterial pyrimidine biosynthesis
ATCase
first enzyme in pyrimidine de novo synthesis pathway
what does ATP prevent
CTP-induced change in ATCase activity
CTP
causes extreme decline in ATCase activity
ribonucleotides
are precursors of deoxyribonucleotides
E coli ribonucleotide reductase
enzyme acts on ribonucleotide diphosphate
what does the reduction involve
replacement of 2OH with H
slide 12
where does regulation of ribonucleotide reductase occur
at primary AND substrate specificity sites
why does ribonucleotide reductase have 2 sites of regulation
idea is to provide a balanced pool of precursors for DNA synthesis
