Biochemistry: Chemical Reactions and Enzymes

Chemical Rxns & Enzymes Metabolism – all of the chemical reactions that occur in an organism (these reactions involve energy!) All reactions in a cell need a jump-start of energy to make them happen – this is called activation energy (car battery)

C. The activation energy is usually too big for cellular reactions to happen on their own. So… 1. Enzymes decrease the activation energy for a reaction, and therefore… 2. Enzymes make chemical reactions happen faster!

D. Enzymes are special proteins 1. Enzymes have an active site that has a special shape designed to fit with a certain molecule (lock and key) 2. The molecule that an enzyme acts upon (and fits together with!) is called the substrate

3. When the substrate binds to the active site, the reaction takes place (induced fit) The enzyme squeezes on the substrate This weakens the bonds in the substrate so they are easier to break Lowers activation energy Induced fit animation (fast forward half-way)

E. Enzymes work best at certain (optimal) temperatures and pH values Why does an increase in temperature make the reaction happen faster for a while, but then suddenly decrease?

Why does the reaction slow down as you move away from the optimal pH? What’s the whole point? It’s all about the shape of the enzyme! If the enzyme changes shape, then the substrate can’t fit in the active site.

Let’s review… Summarize three key items you learned today about enzymes: