Table of Contents
Enzymes are remarkable molecules that are involved in almost every reaction that happens inside us- from DNA replication to the digestion of our food.
Understanding how enzymes work can help us appreciate their significance in facilitating some of the most complex chemical reactions that are essential to our well-being.
How do enzymes work?
A chemical reaction is simply a conversion. Reacting substances, called reactants, convert into a different product or products. Every reaction needs a minimum amount of energy for this conversion to take place, called activation energy.
Some reactions need so much energy that it becomes quite impossible to provide. The only viable option is to reduce the activation energy, and this is done using compounds called catalysts. In living organisms, proteins known as enzymes are catalysts. They are biological catalysts that increase the speed at which a reaction takes place by decreasing the activation energy .
How can you tell if a protein is an enzyme? Enzyme names usually end with the suffix “-ase,” for example, sucrase acts on sucrose (the major component of sugar). Enzymes are highly specific in their function and act only on a specific substance. This substance is called the substrate . An enzyme can and will cause only a certain reaction or a certain type of reaction to take place.
Enzymes are present as inactive protein forms called apoenzymes. The apoenzyme is activated to form a holoenzyme when a cofactor binds to it.
Generally, the action of an enzyme can be divided into multiple steps:
- The enzyme grabs the substrate
The holoenzyme has an active site where a substrate is held to the enzyme. You can imagine the binding site like a Velcro strap. The binding site forms temporary chemical bonds (hooks of the Velcro) with the atoms of the substrate (loops of the Velcro). These bonds help in reducing the activation energy and speed up the reaction – sometimes even by a million times!
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.
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 substrate and enzyme form a complex
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.
- Substrates are converted to products
This process is called catalysis. 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.
The best conditions:
Now that we know how enzymes work, we need to think about when enzymes work best.
Proteins are quite fragile. They cease to perform their functions when the conditions aren’t favorable. Enzymes are no exception. Most enzymes in the human body work best at 98.6°F (37°C). At higher or lower temperatures, enzymes work much more slowly.
The pH of the surroundings matters too. In highly acidic or basic conditions, the structures of enzymes change. The active sites morph too, making the enzymes useless.
For example, enzymes in the stomach, like trypsin, work better in the presence of an acid, but enzymes in the intestine, like lipase, work in basic conditions. Many believe that the acid in the stomach helps digest food; however, that is not the case. The acid provides an acidic environment only.
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.
Did you know that blood carries carbon dioxide back to the lungs before we expel it? An enzyme called carbonic anhydrase plays a major role in this process.
Some enzymes in the human body, and what they do:
Amylase: Present in the saliva, this enzyme digests some of the starch into sugars.
Trypsin: Trypsin digests proteins and produces chains of smaller units, called polypeptides, in the stomach.
Rennin: This enzyme, present in the stomach, helps in digesting proteins in milk. Infants produce this enzyme in greater amounts than adults.
Lipase: Lipases are present in the small intestine and digest fats.
Carbonic anhydrase: Carbonic anhydrase is present in blood, and it converts carbon dioxide into bicarbonate using water.
How enzymes work : A short animation video
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.
Hands-on Science
- Take a piece of bread and put it into your mouth.
- Chew the bread a bit, before leaving it as it is on your tongue.
If you notice carefully, you will find the bread has sweetened a bit. Why do you think this happened? Is there any enzyme in your saliva that might be causing this?
Glossary
Activation energy: The minimum amount of extra energy required by a reacting molecule to get converted into products.
Replication: The process in which two identical replicas of DNA are formed from an original DNA molecule.
Substrate: The substance an enzyme acts upon.
Flesch Kincaid Grade Level: 8.7
Flesch Kincaid Reading Ease: 59.1
References
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2. Robinson, P. K. (2015, October 26). Enzymes: principles and biotechnological applications. Essays in Biochemistry, 59, 1–41. https://doi.org/10.1042/bse0590001
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 https://www.ncbi.nlm.nih.gov/books/NBK554481/
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. https://doi.org/10.3390/ijms16046694
5. Holyoak, T. (2013). Molecular Recognition: Lock-and-Key, Induced Fit, and Conformational Selection. Encyclopedia of Biophysics, 1584–1588. https://doi.org/10.1007/978-3-642-16712-6_468
6. Bonner, P., & Palmer, T. (2007, April 4). Enzymes. In Biochemistry, Biotechnology, Clinical Chemistry. Woodhead Publishing Limited.
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