Enzyme Dynamics and Metabolic Pathways

Enzymes are biological catalysts and activation energy is the minimum amount of energy required by reactants in order for the reaction to take place. Enzymes increase the rate of chemical reactions whilst remaining unchanged by lowering the activation energy needed for the reaction to go ahead. Enzymes are made up of proteins which are folded into complex shapes which allow smaller molecules to fit into them. These smaller molecules fit into the active site of an enzyme. The active site is the place in which the specific substrate molecules bind and the chemical reaction is carried out. The chemical structure and bonds between amino acids determines the shape of an active site.

All metabolic pathways are controlled by enzymes. In metabolic pathways, the substrate is altered at each step to achieve the final product. Almost all metabolic pathways are reversible. Sometimes a substrate or specific enzyme isn’t available at a point in a pathway but the end product can still be made by using an alternative route.

Two types of metabolic pathway are anabolic and catabolic. Anabolic pathways need energy to build up small molecules to larger ones. Catabolic pathways produce energy when breaking down large molecules to smaller ones.

There are many factors which affect enzyme activity. These include: temperature, pH, enzyme concentration, substrate concentration and the presence of inhibitors or activators.

An inhibitor decreases the rate of an enzyme controlled reaction. Competitive inhibitors and non-competitive inhibitors are two common types of inhibitors.

• Competitive inhibitors. The inhibitors molecules bind to the active site to block the substrate molecules from binding to the active site. The molecular structure of competitive inhibitors is similar to that of the substrate so it can fit in the active site and block the substrate.
• Non-competitive inhibitors. The inhibitor reduces the activity of the enzyme and binds equally well to the enzyme whether or not it has already bound the substrate. The inhibitor may bind to the enzyme whether or not the substrate has already been bound, but if it has a higher affinity for binding the enzyme in one state or the other, it is called a mixed inhibitor.