Do you think a charger would be a good example for mitochondria?

not really because mitochondria break down and convert material into energy. a charger just resembles pulling energy from a bigger source.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products