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Chemistry LibreTexts

General Principles

Enzymes are biological catalysts and functional proteins. Enzymes contain specificity in its protein structure in order to have its specialized function. It usually contains more than one subunit and they are critical to sustain life. Enzymes can increase the chemical reactions in living cells. However, enzymes are not consumed in the reaction and their main function is to assist in bringing the substrates together so they can undergo normal reaction faster.


The first enzyme was found in the process of fermentation in milk and alcohol during the nineteenth century. Later in the early 1830s, the term enzyme was used to replace the term ferment. Some scientists believe that ferments must contain living cells and some think ferments could be non-living cells. Finally, in the 1920s, Sumner purified the structure of enzyme and then properties of enzyme then was more clearly understood. Until today, enzymes are still the popular research field that many people are subject to study. 

Structure and Function

Enzymes are proteins, which are made up of amino acids. Enzyme subunits assemble in such a way to allow the enzyme to function. An enzyme has an active site, and the rest of the protein structures function simply as scaffolding. Enzymes have cofactors (eg. metals) or coenzymes which aid in regulations.

In a reaction mechanism, substrate binds to enzyme to form product. These are called enzyme-catalyzed reactions, and the enzymes are not consumed in the reactions itself, but are rather released at the end of the reactions to be recycled. Enzymes have active sites where reactions take place. Many enzymes exhibit stereochemical specificity, and therefore distort substrate to conformation of transition state and enzyme also change and alter affinity of other binding site. Once substrate binds to the active site, the enzyme changes conformation. After the substrate-enzyme complex formed, the chemical reactions can occur further which allow the products to form. There is a small loss of entropy when substrate and enzyme bind and form an active complex; however, the overall entropy increases. The way in which enzymes allow the products to form are complex. The following are some of the ways it could affect the transition states:

  1. Increasing the net entropy of the reactions: Enzymes increase entropy of a reaction by bringing two or more substrates together  in an organized manner in a manner not naturally likely.
  2. Form an intermediate with the substrate that it has bound.


3. Decrease the activation energy or the amount of energy required for the reaction to proceed.



Factors that affect the rate of enzyme reactions

  1. Temperature : Some enzymes only function well at a specific temperature. Having the optimum temperature will help increase the rate of reactions. The substrate and enzyme molecules increase collision frequency and kinetic energy and contribute energy to overcome the activation barrier
  2. pH: pH affects the charge of amino acids at active sites which could alter the binding of a substrate. At the right pH, the enzyme will be able to bind at the active site faster so an increase of reaction rate is more likely to occur. Vice versa, if the pH was too high or low, that changes the charge on the amino acid at active site and that deactivates the active site which no longer allows the enzyme to bind.
  3. Enzyme concentration: An increase of enzyme concentration will also increase the chances of substrate-enzyme binding. 
  4. Substrate concentration: An increase the substrate concentration will also increase the chances of substrate-enzyme binding.
  5. Inhibitors: inhibitors will inhibit the activity of enzyme and decrease the rate of reaction.  Enzyme inhibitors will bind to enzyme active sites and could modify the chemistry of an active site which can stop a substrate from entering.


Applications of enzymes

Enzymes are essential to maintain homeostasis because any malfunction of an enzyme could lead to diseases. Therefore, pharmaceutical companies study enzyme to manipulate and synthesis new medicine. Besides their medicinal applications, enzymes in industry are important because enzymes help breaking down cellulose, wastes, etc. Enzymes are essential in the process of making new products in many industries such as pharmaceutical, food, paper, wine, etc.


  1. "Chapter 4 Enzyme."Copyrighted IHW, Oct. 2005. Web. 5 Mar. 2011.
  2. Chang, Raymond. Physical Chemistry for the Biosciences. Sausalito, CA: University Science Books, 2005. Pages 363-384.