Enzymes are catalysts in living cells; proteins that speed up chemical reactions. Without enzymes, cellular reactions would occur at a much slower rate or not at all; making life impossible.
* Enzyme Substrate Complex *
The word catalyst is a general term for something that speeds up a chemical reaction without being used up, or consumed, in the process. Unlike inorganic catalysts such as acids, bases and metals, enzymes are very specific. Each type of enzyme can interact with only one particular compound, its substrate.
A substrate is a specific reactant in an enzyme-mediated chemical reaction; the reactant that interacts with the enzyme. When the substrate is being acted upon by the enzyme, the interaction is known as the enzyme-substrate complex.
* Lock and Key Model *
Each enzyme has a unique three dimensional shape, including a surface groove called an active site. The active site is where the substrate interacts with its enzyme, and the active site of each type of enzyme fits its target substrate much like a key fits in a lock. Most other chemical substances will not fit in the enzyme’s active site.
* Activation Energy *
Enzymes work by weakening substrate bonds, which lowers activation energy (amount of energy necessary for the reaction to occur). The enzyme then releases the product and is ready to begin the process again. An enzyme molecule can catalyze the same reaction over and over, transforming many substrate molecules. You can think of an enzyme as a piece of equipment that can be used repeatedly to help a specific reaction occur.
In summary, enzymes are:
* catalysts that accelerate cellular reactions
* not permanently changed in the reactions they mediate
* specific to what they will catalyze
* usually named with an ‘-ase’ suffix, such as amylase, maltase, catecholase
* Examples of Enzymes in Action *
1. Enzymes and Digestion: The food that you eat is exposed to enzymes from beginning to end. The enzyme amylase works in your mouth while you chew, breaking down starch (a big sugar) into smaller sugars. In your stomach, food is exposed to acidic gastric juices which contain the enzyme pepsin. Even in the highly acidic environment of the stomach, pepsin functions to split proteins.
Pancreatic juice released into the small intestine, neutralizes the acid from the stomach, and contains an enzyme that continues to break down sugars; another that breaks down proteins; and a third, that digests fat. Once the food moves on to the small intestine, it has been broken down into tiny nutrients that the body can absorb and use for energy, repair and growth.
2. The Browning of Fruits and Vegetables: Catecholase is an enzyme present in most fruits and vegetables. It facilitates the browning of cut or bruised produce by catalyzing a reaction between the molecule catechol and oxygen in the atmosphere. The product of this reaction is called polyphenol, the brown substance that can be seen accumulating when apples or potatoes are exposed to air.
3. Fresh Pineapple and Jell-O: Have you even tried to make Jell-O with fresh pineapple in it? If so, you’ve been disappointed. Here’s why.
Jell-O is made of gelatin, a processed version of a structural protein called collagen that is found in many animals, including humans. The gelatin you eat in Jell-O comes from the collagen in cow or pig bones, hooves, and connective tissues.
Pineapple contains the enzyme bromelain, which can digest protein. If fresh pineapple is added to Jell-O, the bromelain breaks down the gelatin’s protein, and the Jell-O will not solidify upon cooling.
If canned pineapple is used instead, the Jell-O sets just fine. This is because the heat of the canning process denatures, or changes the shape of proteins, and an enzyme’s shape is crucial for the substrate to precisely fit into its active site. In canned pineapple, the bormelain has been denatured; the enzyme’s shape has changed and it can no longer facilitate the breakdown of gelatin.
* More Information on Enzymatic Activity and Organic Molecules *
McGraw Hill Enzyme Animations
Chem4Kids (Even though this site is designed for children, it is a great resource for chemistry neophytes of any age.)