Coenzyme: Definition & Function Video

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  • 0:05 What is a Coenzyme?
  • 1:16 The Function of Coenzymes
  • 3:27 Sources of Coenzymes
  • 5:25 Lesson Summary
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Lesson Transcript
Instructor: Darla Reed

Darla has taught undergraduate Enzyme Kinetics and has a doctorate in Basic Medical Science

This lesson defines what a coenzyme is and how it relates to enzymes. It also discusses the functions of a coenzyme and gives some information as to where coenzymes can be found.

What is a Coenzyme?

Coworkers can be very helpful when you have a question or a problem. They might even help you get adjusted if you're new to the job. The co- in coworkers means 'together,' or 'with,' so coworkers are people you work with. So what do you suppose coenzyme might mean? It means 'with an enzyme.' A coenzyme works together with an enzyme.

What is an enzyme? Enzymes are proteins that can increase the speed of a chemical reaction that would normally occur over a longer period of time. In other words, enzymes make things happen faster. Enzymes don't always work alone, though. They have helpers called cofactors. Cofactors can be inorganic ions (like zinc) or non-protein, organic (carbon-containing) molecules. The latter are called coenzymes.

Coenzymes bind to the enzyme and assist in enzyme activity. They can bind and react with many different enzymes, so they're not specific to a particular enzyme. They help enzymes change starting elements (substrates) into their final version (products). In doing this, the coenzyme can be changed and often alternates between various forms.

Coenzyme Function

There is a specific location on an enzyme which binds to substrates and helps turn them into products. This location, called the active site, is where coenzymes bind. There are several ways coenzymes assist in enzyme function, including changing their shape to activate, or turn on, enzymes, or aiding in chemical reactions by acting as carriers of energy or molecular groups.

In order to occur, chemical reactions might require or release energy. Remember the First Law of Thermodynamics: energy can neither be created nor destroyed. So, for an enzyme to function, sometimes energy is needed. The cell likes to be efficient in its use of energy; therefore, it tries to capture and reuse energy. One of the ways it does this is through coenzymes.

Let's look at an example. The molecule ATP (adenosine triphosphate) can function as a coenzyme. When a phosphate group is removed, turning ATP into ADP (adenosine diphosphate), energy is released. Since many chemical reactions require energy, cells can use ATP to give energy to a reaction to assist in changing the substrate to product. The substrate can be temporarily phosphorylated, or have an added phosphate group. The phosphate group can then be removed and the product is formed partly through the addition and removal of a phosphate.

Coenzymes often have long complicated names and are frequently shortened to acronyms or abbreviations. Coenzymes with shortened names include: NAD+/NADH, NADP+/NADPH, and FAD/FADH2. These function similarly to ATP, except instead of a molecular group, they remove or add electrons and hydrogen atoms. Hence, they have two different forms: NAD+ and NADH are the same molecule, except NADH has an added hydrogen. Also, the removal or addition of electrons can change their shape, allowing them to bind or dissociate (be removed) from an enzyme they are helping.

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