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exergonic vs endergonic processes
exergonic: release en. eg. cell respiration, catabolic rxns
endergonic: take in/absorb en. eg. photosynthesis, anabolic rxns.
how do enzs speed up the rate of a rxn?
enz destabilises critical bonds within the sub → encourages bonds to break & facilitates rearrangement of atoms → form prods. brings sub & enz in close proximity. lowers en level of the sub’s transitionary state → more stable → easier for rxn to occur.
enz inhibitors
regulate & control enz activity
competitive i
similar structural resemblance
compete for as
bind to as → enz-i complex → prevents sub from bonding → lowers rxn rate
is temporary (weak bonds)
increase conc of sub → can out compete by increasing chance of collision
non-competitive i
no structural resemblance
binds to enz in a region other than as → alters 3d shape & as → prevents sub from bonding → lower rxn rate
eg. for inhibitors
competitive: dihydropteroate synthetase, para-aminobenzoate, sulfadiazine
nc: phosphofructokinase, fructose-6-phosphate, xylitol-5-phosphate.
allosteric enzs
designed to change shape → cmpds bind to allosteric sites → modify enz’s activity → prevent subs from binding
end product inhibition
the end product acts as an inhibitor of an enz that catalyses an initial step in the pathway
accumulation of end product → inhibits the enz → lower production of the end product
adv: prevents buildup of intermediate products, the pathway can be switched off completely in cells w an excess.
eg. threonine → isoleucine, which inhibits threonine deaminase
