1.One particular analogy I use is when explaining the fact that enzymes are catalysts.
A cake mixer is used to mix the ingredients of a cake faster. However it does not become part of the cake itself.
Enzymes make a reaction go faster but they do not form part of the reaction itself.....enzymes are instruments.....they are catalysts.
2. I find the Lock and Key model explaining the specificity of enzymes very clear. I literally refer to the lock and key in the lab door......that there is one paricular key for that lock.....so one particular substrate for one particular active site.
I use analogies to clarify a point...but would change it if students are lead to misconceptions.
Good day...even though it's raining!!