What is Acetylcholinesterase? - Function & Definition

Instructor: Korry Barnes

Korry has a Ph.D. in organic chemistry and teaches college chemistry courses.

This lesson introduces a biological enzyme called acetylcholinesterase. Our primary points of discussion will center around its definition and how it functions at the cellular level.

Speed Makes all the Difference

Are you familiar with the old story of ''The Tortoise and the Hare?'' In this fictional tale, a rabbit challenges a tortoise to a race. Rabbits are much faster than tortoises, but this one becomes cocky and decides to take multiple breaks along his way to the finish line. At the end of the story, we learn that ''slow and steady wins the race'' when the slow but steady tortoise defeats the fast but flighty hare. It's a useful lesson, but it doesn't always apply: if this parable was played out by the enzymes in your body, for example, you'd be dead.

In terms of biological systems, it turns out that speed is actually everything. You see, the chemical reactions that take place within the cells of our bodies are what allow us to live and function properly, and the rate at which those reactions happen is everything. The biological chemical reactions that we depend on for life are facilitated by what are called enzymes; without them, reactions would unfold so slowly that life simply wouldn't be possible. Today we are going to be discussing a specific enzyme called acetylcholinesterase and its function at the cellular level.

Acetylcholinesterase Is an Enzyme

Probably the most important thing to realize about acetylcholinesterase is that it's classified as an enzyme. But what exactly does that mean? Enzymes are biological catalysts whose role is to speed up chemical reactions within the cells of biological systems. The compounds that enzymes act on are usually called substrates, and the enzyme always converts the substrate to a product of some sort. As we previously mentioned, without enzymes essential biological reactions would occur so slowly that life would not be possible.

In a typical enzyme-promoted reaction, the substrate (or substrates) combines with the enzyme and undergoes a chemical reaction. This is called an enzyme-substrate complex. Once the reaction is complete the products are released from the complex, making room for more substrate molecules to bond to the enzyme and repeat the process.

A generic example of an enzyme-substrate reaction scheme.

Acetylcholinesterase is an enzyme whose primary function is to catalyze and promote the breakdown of a neurotransmitter called acetylcholine. Neurotransmitters are organic compounds that serve as signal molecules or chemical messengers, and their job is to help facilitate communications between nerve cells and muscle cells. When this breakdown event occurs, the two products that result are choline and acetic acid. They are then further metabolized (broken down) or recycled by the cell.

The chemical structure of acetylcholine.

Most enzymes are very large structures; they are often modeled using what are called ribbon diagrams. Although it just looks like chaos, the ribbons in the diagram of actylcholinesterase represent the long chains of amino acids that make up the enzyme. Since enzymes are built from many chains of these amino acid building blocks, they are classified as proteins.

Acetylcholinesterase ribbon diagram

How Does Acetylcholinesterase Function?

When a neurotransmission event takes place, molecules of acetylcholine are released from neuron cells and bind to receptor sites (active sites) on muscle cells. The result is much like what happens when a light switch is turned on in a room: once the switch is flipped, electricity flows within the wires until it reaches the light bulbs and the light turns on. The function of acetylcholinesterase is to catalyze the breakdown of acetylcholine molecules once the communication between the neuron and the muscle cell is complete.

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