What Is an Enzyme?

Enzymes

Enzymes are macromolecules that help to speed up reactions. Although most enzymes are proteins, there are several exceptions (such as ribozymes). There are thousands and thousands of different enzymes, but luckily for us, most enzyme names end in "-ase," such as lactase, sucrase, and peroxidase.

The Role of Enzymes

Enzymes act as catalysts, which speed up reactions without being consumed in the process. That's right—enzymes can do the same thing over and over again without being used up! Catalysts work by lowering the activation energy of a reaction, or the minimum energy needed for a reaction to proceed.

Enzymes and Substrates

Enzymes have specificity, meaning that they can't just speed up any reaction. They can only speed up certain reactions where the reactants can bind to the enzyme.

The reactant is known as the substrate and when the enzyme binds to the substrate(s), an enzyme-substrate complex is formed.

The substrates bind to the enzyme's active site, typically a pocket or groove on the enzyme's surface, causing the enzyme to alter its shape slightly to fit more snugly around the substrate. Other substrates cannot "fit" into this active site, allowing the enzyme to be specific only when the substrate is present.

How Enzymes Work

Enzymes act as catalysts, but how do they speed up reactions?

There are actually several ways:

(1) If there are multiple substrates, the enzyme provides a way for the substrates to be close to each other and in the proper orientation

(2) Since the enzyme is tightly gripping the substrate, it could stretch the bonds that hold the substrate molecules together, stressing, or even breaking, bonds that need to be broken for the reaction to occur

(3) The enzyme may provide a different microenvironment favorable to the reaction (i.e. a different pH)

** (4)** Sometimes, the enzymes' amino acids may briefly bond with the substrate and partake in the reaction

Enzymatic Activity

Enzyme activity, as you might be able to guess, depends a lot on the environment that the enzyme-substrate complex is in. The two main factors that affect enzymatic activity are pH and temperature.

Generally, increasing the temperature will increase the enzymatic activity. However, after a certain point, the temperature will be so hot that it disrupts the enzyme's actual structure, causing the enzyme to denature, or lose its shape (and thus its function).

In addition, the optimal pH for enzymes is typically between 6 and 8. Again, too low or too high of a pH will cause the enzyme to denature.

However, there are exceptions to these rules if you look at the graphs of optimal pH/temperature enzymatic activity above.

Say, for example, the enzyme pepsin in your stomach works in stomach acid, which has a pH of approximately 2. Or take the enzymes in thermophilic (heat-loving) bacteria, which are often able to work at temperatures of 70 degrees Celsius or higher!

What is an enzyme? An enzyme is a molecule - often a protein - that acts as a catalyst in biochemical reactions. This means an enzyme speeds up these reactions. Enzymes are named with the suffix "-ase", such as in "phosphorylase."

Why do we need enzymes? As biological beings, our bodies - and the bodies of all living things - are made possible by the interplay of chemical reactions. For example, reactions in the retina of the eye allow us to detect edges, and reactions in the nervous system synthesize neurotransmitters (molecules that allow neural cells to communicate.) Imagine if those things didn't happen quickly!

Chemical reactions often happen slowly without catalysts. This is because even energetically favorable reactions have an activation energy, or a certain threshold of energy that must be overcome for the reaction to take place.

You can think of this like a roller-coaster. Going straight down isn't as much fun as going up first!

However, as much fun as a tall roller-coaster might be, it requires a good amount of energy to get the coaster car to that higher point - activation energy! Analogously, it takes a good amount of energy to bring the reactants to the higher energy state. So, reactions will often happen slowly if not catalyzed. This is where enzymes and other catalysts come in - they lower the activation energy.

Without enzymes, biological reactions might need very high temperatures or extreme pHs to occur quickly and efficiently. But the body does NOT want these things - extreme temperatures of pHs can cause proteins to denature, or lose their structure.

So, how do enzymes work? Enzymes have active sites where substrates - the molecule or molecules who's reaction the enzyme catalyzes - bind. Enzymes are substrate-specific: the active site is shaped to fit a specific substrate. This active site often brings together substrates in the proper orientation for them to react. Remember, for chemical reactions to occur, reactants must collide in certain ways in space.

Enzymes also have optimal temperatures and/or optimal pHs at which they work their best - think of this like a habitat. Animals sometimes survive in several different habitats, but they do best in one specific one. Enymes are the same way - they might function at a somewhat different temperature or pH than their optimal one, but they will not be functioning at their best.