Enzymes are made up of proteins folded into complicated shapes; They are present throughout the body. The chemical reactions that keep us alive, our metabolism, depend on the work of enzymes. Enzymes speed up (catalyze) chemical reactions; In some cases, enzymes can make a chemical reaction millions of times faster than it would have been without them. A substrate binds to the active site of an enzyme and is converted to products. Once the products leave the active site, the enzyme is ready to bind to a new substrate and repeat the process.
What do enzymes do?
The digestive system: Enzymes help the body break down larger complex molecules into smaller molecules, such as glucose, so the body can use them for fuel.
DNA Replication: Every cell in your body contains DNA. Every time a cell divides, that DNA needs to be copied. Enzymes help in this process by unwinding the DNA coils and copying the information.
Liver enzymes: The liver breaks down toxins in the body. To do this, it uses a variety of enzymes.
The “lock and key” model was first proposed in 1894. In this model, the active site of an enzyme has a specific shape, and only the substrate will fit into it, like a lock and key. This model has now been updated and is called the induced fit model. In this model, the active site changes shape as it interacts with the substrate. Once the substrate is completely locked and in the exact position, catalysis can begin.
Enzyme mechanism of action
In most chemical reactions, there is an energy barrier that must be overcome for the reaction to occur. This barrier prevents complex molecules such as proteins and nucleic acids from spontaneously degrading, making it necessary for the preservation of life. However, when metabolic changes are required in a cell, some of these complex molecules must be broken down and this energy barrier must be overcome. The heat could provide the extra energy needed (called activation energy), but the increased temperature would kill the cell. The alternative is to lower the activation energy level by using a catalyst. This is the role that enzymes play. They react with the substrate to form an intermediate complex, a “transition state,” that requires less energy for the reaction to occur.
The unstable intermediate compound rapidly decomposes to form reaction products, and the unchanged enzyme is free to react with other substrate molecules. Only a certain region of the enzyme, called the active site, binds the substrate. The active site is a groove or pocket formed by the protein’s folding pattern. This three-dimensional structure, along with the chemical and electrical properties of the amino acids and cofactors within the active site, allows only a particular substrate to bind to the site, thus determining the specificity of the enzyme.
The synthesis and activity of enzymes are also influenced by genetic control and distribution in a cell. Certain cells do not produce some enzymes and others are formed only when they are required. Enzymes are not always found uniformly within a cell; they are often compartmentalized in the nucleus, in the cell membrane, or in subcellular structures. The rates of enzyme synthesis and activity are further influenced by hormones, neurosecretions, and other chemicals that affect the internal environment of the cell.
The perfect conditions
Enzymes can only work under certain conditions. Most enzymes in the human body work best around 37°C, body temperature. At lower temperatures, they will still work but much more slowly. Similarly, enzymes can only function in a certain pH range (acid/alkaline). Their preference depends on where they are located in the body.
For example, enzymes in the intestines work best at a pH of 7.5, while enzymes in the stomach work best at a pH of 2 because the stomach is much more acidic. If the temperature is too high or the environment is too acidic or alkaline, the enzyme changes shape; this alters the shape of the active site so that substrates cannot bind to it: the enzyme has become denatured.