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 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.
Even though enzymes are specific, some work in groups as multi-enzyme complexes which means that these enzymes can work with more than one substrate. When a reaction involves multiple substrates, the active site will orientate the reactants to put them in the correct position for the reaction to take place. When a substrate binds to an active site, the active site slightly changes shape – this is known as induced fit. This process makes sure the substrate and the active site come into closer contact to improve the chances of the reaction taking place. The substrate has a high affinity for the active site and the product has a low affinity for the 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. The direction of the reaction is determined by the concentration of reactants verses products. 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. An increase in substrate concentration increases the reaction rate when a competitive inhibitor in absent. When a competitive inhibitor is present, an increase in substrate concentration reverses the effects of competitive inhibition as it causes a gradual increase in reaction rate. This is because there are more substrate molecules to fill active sites (as opposed to inhibitors filling the active sites).
Non-competitive inhibitor—> These inhibitors do not combine with the active site of an enzyme. They attach to an allosteric site which alters the shape of the active site so the substrate molecules cannot combine with the active site. The greater the number of enzyme molecules affected, the slower the reaction. Each year there are many children found to be suffering from lead poisoning. This is high levels of lead in the blood or bones. It can lead to many symptoms: headaches, stomach aches, anaemia. Also, high levels of lead in the blood can affect the development of a child’s brain. Young children and babies are at a higher risk of suffering from lead poisoning than adults. Lead can affect the body by inhalation, swallowing or by absorption through the skin. Lead found in the bones can affect how much calcium the body absorbs which the bones need to grow strong.