the part where the enzyme joins to the substrate to catalyse the reaction
it’s called the lock and key model because the substrate fits into the enzyme like a key fits into a lock
what affects the rate of an enzyme catalysed reaction

temperature, ph and substrate concentration
changing the temperature will increase the rate as the enzymes and substrate have more energy so they move more and are more likely to collide. if it gets too hot the enzyme will become denatured
