How Do Enzymes Work?

Table of Contents

What are enzymes?

Enzymes are protein molecules that are found in all living organisms. They are biological catalysts that increase the speed at which a reaction takes place by decreasing the activation energy. Enzyme names usually end with the suffix “-ase.” Enzymes are highly specific in their function. An enzyme can and will cause only a certain reaction or a certain type of reaction to take place.

A ribbon diagram of an enzyme
A ribbon diagram of an enzyme, Credit: Wikimedia/Yikrazuul

Enzymes are classified based on the type of reaction they bring about and the function they perform. Enzymes that help in the transfer of electrons from one compound to the other are called oxidoreductases. Transferases contain the word “transfer,” making it easier to understand that they transfer groups of atoms between compounds. An easy way to remember the function of hydrolases is by looking at the name. “Hydro” means water, therefore hydrolases are enzymes that break compounds with the help of water. Enzymes that join compounds together are called ligases (think “ligate.”) Isomerases are enzymes that rearrange compounds into their isomers. Lyases introduce new bonds and ring structures into compounds. 


Enzymes that aid in the movement of ions and molecules are known as translocases (from the word “translocate.”)

Enzymes are present as inactive protein forms called apoenzymes. The apoenzyme is activated to form a holoenzyme when a cofactor binds to it. The holoenzyme has two sites that are critical for the reaction to progress. The first is a binding site, at which a substrate is held to the enzyme. The second is an active site, at which the enzyme and substrate react to form products. Together, they are known as the catalytic site. The reaction will not take place unless the substrate is positioned correctly in the catalytic site. 

The fundamental subunits of an enzyme
The fundamental subunits of an enzyme, Credit: Wikimedia/Moniquepena

How do enzymes work?

The specific nature of enzymes led to many questions among scientists working on enzymes, the main one being, “How does an enzyme bind to a substrate?” Two theories were put forth to answer this question.


The first one was known as the “Lock and Key” hypothesis, proposed by Emil Fischer in 1894. According to this theory, a substrate fits into the catalytic site of an enzyme the way a key fits into a lock. This theory was not accepted.

The Lock and Key Model; the enzyme and substrate have complementary structures
The Lock and Key Model; the enzyme and substrate have complementary structures, Credit: Wikimedia/Stephjc

In 1958, Daniel Koshland came up with the “Induced-Fit” model of substrate binding. In this theory, the enzyme is said to change its structure in order to bind to the substrate. This is similar to how a glove fits a hand. The glove is floppy until worn, after which it takes the shape of the hand. In this analogy, the enzyme is the glove and the substrate is the hand.

The Induced-Fit hypothesis; the enzyme fits around the substrate the way a glove fits on a hand
The Induced-Fit hypothesis; the enzyme fits around the substrate the way a glove fits on a hand, Credit: Wikimedia/Kevin Olson

Now that we have learned that enzymes change their structure to fit the substrate, we need to understand how exactly they work. Once the enzyme has attached to the substrate in the correct position, it forms an enzyme–substrate complex. This complex is unstable and exists only for a few seconds before the enzyme converts the substrate into products and detaches from the products.

The formation of the E–S complex and products
The formation of the E–S complex and products, Credit: Wikimedia/Aejahnke

The mechanism of product formation involves a series of bond-breaking and bond-forming processes between the enzyme and substrate. This changes the structure and properties of the substrate and converts it into products. The enzyme does not undergo any permanent changes during these reactions.

Enzymes in the Human Body

The human body hosts a variety of enzymes without which we would not be able to survive. Digestion requires a large number of enzymes working together to make sure we get the energy we need from the food we eat. Digestive enzymes include carbohydrases that break down carbohydrates into simple sugars, proteases that break down proteins into amino acids, and lipases that break down fats into fatty acids and glycerol.

The liver is a major hub of enzymes that degrade toxic substances into substances that can be easily removed from the body. These enzymes belong to the cytochrome P450 family of enzymes.

Within the nucleus of our cells is a group of enzymes that help in DNA replication, transcription, and translation. These processes are necessary for the growth and progression of human life.

Enzymes in the Industry

Enzymes play a very important role in the food and beverage industries in the production of alcohol, jams, breads, and dairy products. Funnily enough, the word “enzyme” was given by Wilhelm Kühne in 1878 while he was observing the process by which yeast converts sugar into alcohol.

Alcohol fermentation tanks
Alcohol fermentation tanks, Credit: Wikimedia/David

Enzymes like pectinases, which are extracted from fungi, are used in the preparation of jams and jellies. Acid proteases, found in the fungus Aspergillus niger, help in cheese making. In the alcohol industry, enzymes like lactate dehydrogenase, pyruvate decarboxylase, and alcohol dehydrogenase are used.

Aspergillus niger under the microscope
Aspergillus niger under the microscope, Credit: Wikimedia/Alexander Klepnev

The pharmaceutical industry also utilises enzymes for the manufacture of medicines and drugs. Penicillin acylases are used in the production of penicillin. Insulin is produced on an industrial scale using enzymes like trypsin and carboxpeptidase B.

Short Animation


Enzymes are molecules that are required by all living organisms. They have a wide range of applications and play important roles in life processes. They have also been utilised in major industries for food, beverages, and drugs, among other things.


Activation energy: The minimum amount of extra energy required by a reacting molecule to get converted into products.


Isomers: Compounds having the same number of atoms but differing in their structure.


Replication: The process in which two identical replicas of DNA are formed from an original DNA molecule.


Substrate: The substance an enzyme acts upon.


Transcription: The process by which DNA is converted to mRNA.


Translation: The process of protein synthesis from mRNA.

Flesch Kincaid Grade Level: 8.7


Flesch Kincaid Reading Ease: 59.1

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2. Robinson, P. K. (2015, October 26). Enzymes: principles and biotechnological applications. Essays in Biochemistry, 59, 1–41.


3. Lewis, T., & Stone, W. L. (2022, April 28). Biochemistry, Proteins Enzymes – StatPearls – NCBI Bookshelf. Biochemistry, Proteins Enzymes – StatPearls – NCBI Bookshelf. Retrieved October 14, 2022, from


4. Schneider, H.-J. (2015, March 25). Limitations and Extensions of the Lock-and-Key Principle: Differences between Gas State, Solution and Solid State Structures. International Journal of Molecular Sciences, 16(12), 6694–6717.


5. Holyoak, T. (2013). Molecular Recognition: Lock-and-Key, Induced Fit, and Conformational Selection. Encyclopedia of Biophysics, 1584–1588.


6. Bonner, P., & Palmer, T. (2007, April 4). Enzymes. In Biochemistry, Biotechnology, Clinical Chemistry. Woodhead Publishing Limited.

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  • Sanjana Kadur

    Sanjana is doing her masters in biochemistry. She loves all things biology and truly believes that dogs make the world a better place. She enjoys playing basketball and spends most of her evenings on the court. Writing for Smore Science gives her the creative freedom to write about science in a fun and relatable way.