8.1 metabolism

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