enzyme activity can be inhibited by enzyme inhibitors- molecules that bind to the enzyme that they prevent from functioning. this can be competitive or non-competitive.

competitive inhibition

competitive inhibitor molecules have a similar shape to that of the substrate molecules
they compete with the substrate molecules to bind with the completementary active site, but no reaction takes
instead they block the active site, either temporarily or permanently, so no substrate molecules can react
how much the enzyme is inhibited depends on the relative concentrations of the inhibitor and the substrate
if theres a high concentration of inhibitor, itll take up more of the enzymes and so the rate of reaction will slow
if theres a high concentration of substrate, then its chances of getting to an active site before the inhibitor increase. so increasing the substrate will increase the rate, to a point

non-competitive inhibition

non competitive inhibitor molecules bind to the enzyme at any point, except the active site. the site they bind to is named to allosteric site.
this causes the active site to change shape so the substrate can no longer bind to its active site
they dont 'compete' with the substrate molecules to bind to the active site, because they are a different shape and it can join anywhere else on the enzyme
increasing the concentration of the substrate wont make any difference to the reaction rate because activity will still be inhibited

reversible vs irreversible

this depends on the strength of the bonds between the enzyme and the inhibitor
if theyre strong, covalent bonds, the inhibitor cant be removed easily and the inhibition is irreverisble
if theyre weaker, hydrogen or ionic bonds, the inhibitor can be removed and the inhibition is reversible

some drugs and metabolic poisons are enzyme inhibitiors

some antiviral drugs (to treat viruses like HIV) eg. reverse transcriptase inhibitors inhibit the enzyme revers transcriptase, which catalyses the rplication of viral DNA. this prevents it from replicating
some antibiotics- eg. penicillin inhibits the enzyme transpeptidase, which catalyses the formation of proteins in bacteria cell walls. this weakens the cell walls and prevents the bacterium from regulating its osmotic pressure. as a result, the cell bursts and the bactereium is killed
cyanide is an irreversible inhibitor of cytochrome c oxidase, an enzyme that catalyses respiriation reaction. cells that cannot respire, die, often causing death
malonate inhibits succinate dehydrogenase (which also catalyses respiration reactions)
arsenic inhibits the action of pyruvate dehydrogenase, another enzyme that catalyses respiration reactions

metabolic pathway inhibition

a metabolic pathway is a series of connected metabolic reactions. the product of the first reaction takes part in the second reaction, and so on. each reaction is catalysed by a different enzymes.
many enzymes are inhibited by the product of the reactionthey catalyse. this is known as product inhibition.
end-product inhibition is when the final product in a metabolic pathway inhibits an enzyme that acts earlier on in the pathway.
end-product inhibition is a nifty way of regulating the pathway and controlling the amount of end product that is made. if the concentration of end-product gets too high, the product will inhibit an earlier enzyme to stop the action, until the concentration drops or circumstances change.

	Created by Eleanor Goodsell almost 10 years ago

all info on enzyme inhibition