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They are essential for respiration, digesting food, muscle and nerve function, among thousands of other roles. Each cell in the human body contains thousands of enzymes. Enzymes provide help with facilitating chemical reactions within each cell. Since they are not destroyed during the process, a cell can reuse each enzyme repeatedly. Enzymes help with specific functions that are vital to the operation and overall health of the body. This article reviews what enzymes are and the roles they play in various parts of the body. The basics Share on PinterestTanja Ivanova/Getty ImagesThe majority of enzymes are proteins, though some are Ribonucleic acid (RNA) molecules. RNA molecules translate information from DNA and create proteins. Each cell contains thousands of enzymes, providing specific help throughout the body. Enzymes help with the chemical reactions that keep a person alive and well. For example, they perform a necessary function for metabolism, the process of breaking down food and drink into energy. Enzymes speed up (catalyze) chemical reactions in cells. More specifically, they lower the threshold necessary to start the intended reaction. They do this by binding to another substance known as a substrate. What do enzymes do Enzymes provide support for many important processes within the body. Some examples include:The digestive system: Enzymes help the body break down larger complex molecules into smaller molecules, such as glucose, so that the body can use them as fuel.DNA replication: Each cell in the body contains DNA. Each time a cell divides, the cell needs to copy its DNA. Enzymes help in this process by unwinding the DNA coils.Liver enzymes: The liver breaks down toxins in the body. To do this, it uses a range of enzymes the facilitate the process of destroying the toxins. Other activities enzymes help with include:hormone productioncell regulation creating movement to make the muscle contracttransporting materials around a cellrespirationsignal transduction How enzymes workShare on PinterestEnzyme lock and key model The “lock and key” model was first proposed in 1894. In this model, an enzyme’s active site is a specific shape, and only the substrate will fit into it, like a lock and key. A newer model, the induced-fit model, helps to account for reactions between substrates and active sites that are not exact fits. In this model, the active site changes shape as it interacts with the substrate. Once the substrate fully locks in and in the exact position, the catalysis can begin. The perfect conditions Enzymes can only work in certain conditions. Most enzymes in the human body work best at around 98.6-degrees Fahrenheit (F) (37°C), which is the body’s typical temperature. At lower temperatures, they may still work but much more slowly. If the temperature is too high or if 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. This is denaturing. Different enzymes tolerate different levels of acidity. For instance, enzymes in the intestines work best at around 8 pH, whereas enzymes in the stomach work best at about pH 1.5 because the stomach is much more acidic. Cofactors Some enzymes cannot function unless they attach to a specific non-protein molecule, known as cofactors. There are two types of cofactors, ions and coenzymes. Ions are inorganic molecules that loosely bond to the enzyme to ensure it can function. By contrast, coenzymes are organic molecules that also loosely bond with and allow an enzyme to do its job. When a cofactor bonds tightly with an enzyme, it is known as a prosthetic group. Inhibition To ensure that the body’s systems work correctly, it is sometimes necessary to slow down enzyme function. For instance, if an enzyme makes too much of a product, then the body needs a way to reduce or stop the production. Several factors can limit enzyme activity levels, including:Competitive inhibitors: This inhibitor molecule blocks the active site so that the substrate has to compete with the inhibitor to attach to the enzyme.Non-competitive inhibitors: This molecule binds to an enzyme somewhere other than the active site and reduces how effectively it works.Uncompetitive inhibitors: This inhibitor binds to the enzyme and substrate. The products leave the active site less easily, which slows the reaction.Irreversible inhibitors: This is an irreversible inhibitor, which binds to an enzyme and permanently inactivates it. Examples of specific enzymes Thousands of enzymes in the human body exist to perform around 5,000 different functions. A few examples include:Lipases: This group of enzymes help digest fats in the gut.Amylase: In the saliva, amylase helps change starches into sugars.Maltase: This also occurs in the saliva, and breaks the sugar maltose into glucose.Trypsin: These enzymes break proteins down into amino acids in the small intestine.Lactase: Lactase breaks lactose, the sugar in milk, into glucose and galactose.Acetylcholinesterase: These enzymes break down the neurotransmitter acetylcholine in nerves and muscles.Helicase: Helicase enzymes unravel DNA.DNA polymerase: These enzymes synthesize DNA from deoxyribonucleotides. Types of enzymes Experts break enzymes down into several different types based on the functions they perform in the body. The different types include:oxidoreductasestransferaseshydrolaseslyasesligasesisomerases The body needs all of the different types to function properly. Summary Enzymes play a large part in the day-to-day running of the human body. Enzymes work by combining with molecules to start a chemical reaction. They work best at certain pH levels and temperatures. They play a vital role in the proper functioning of the digestive system, the nervous system, muscles, and more. Last medically reviewed on July 7, 2022Biology / BiochemistryGastroIntestinal / Gastroenterology 6 sourcescollapsedMedical News Today has strict sourcing guidelines and draws only from peer-reviewed studies, academic research institutions, and medical journals and associations. We avoid using tertiary references. We link primary sources — including studies, scientific references, and statistics — within each article and also list them in the resources section at the bottom of our articles. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.1.18: Enzyme function. (2021).https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_Introductory_Biology_(CK-12)/01%3A_Introduction_to_Biology/1.18%3A_Enzyme_FunctionEnzyme. (2022).https://www.genome.gov/genetics-glossary/EnzymeEnzymes in the body. (n.d.).https://corneotherapy.org/articles/enzymes-in-the-bodyKrise, K. M. (n.d.). Enzymes: Moving at the speed of life.https://www.acs.org/content/acs/en/education/outreach/celebrating-chemistry-editions/2021-ncw/enzymes.htmlRobinson, P. K. (2015). Enzymes: principles and biotechnological applications.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4692135/What is dna replication? (2021).https://www.yourgenome.org/facts/what-is-dna-replicationFEEDBACK:Medically reviewed by Avi Varma, MD, MPH, AAHIVS, FAAFP — By Tim Newman — Updated on July 7, 2022 Latest newsWhat sets 'SuperAgers' apart? 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