Are Enzymes Proteins?

Yes. Basically, enzymes are a group of proteins that are able to catalyze reactions. Not all proteins have this property: there are structural proteins, or transport proteins, for instance.

Lately, it has been found that some other molecules too have an ability to speed up chemical reactions, but, as a rule, only catalytic proteins are called enzymes by scientists.

No, enzymes are not amino acids. Amino acids are relatively simple organic molecules. Enzymes, however, are very complex. They are what chemists call polymers. They are molecules that are composed of multiple building blocks that can make long chains.

Enzymes are made of protein chains. These chains, in their turn, are formed by different amino acids. There are 21 amino acids that can be used by the human body to build proteins, and they can be combined in multiple ways. Some enzymes can consist of only one protein, while other enzymes can consist of multiple proteins.

There is also some evidence that RNAs also can work similar to enzymes, but most enzymes are proteins, and we will describe protein-based enzymes here.

Enzymes can be found both inside and outside the cell. There are also antimicrobial and digestive enzymes in saliva, as well as digestive enzymes in secretions produced by the pancreas. Enzymes can be also found in the bloodstream in case of stress or damage to the heart or the liver.

The proteins that work as enzymes are not simple chains. They usually are folded up into complex shapes. The shapes they form are essential. Each protein has a particular area that can participate in reactions with other molecules.

If you look at a wholly formed protein in 3D, it would be the hollow or cleft -like area composed of polar or non-polar amino acids that can specifically interact with a minimal number of molecules. This area is called the active site of an enzyme.

Colloids are gel-like substances. The Cytoplasm of the cell is a colloid made up of different molecules, for example. Due to that property, they are relatively stable chemically and can be isolated with special methods, such as dialysis.

Most enzymes are:

• Sensitive to temperature. They are unable to work if the temperature is lower than a certain threshold, and they get destroyed if the temperature is above 42°C.
• Sensitive to pH. The cell usually has individual compartments with a certain pH, where only specific enzymes can work.
• Sensitive to inhibitory molecules. Specific molecules can interact with the active site of the protein and prevent it from supporting chemical reactions. An inhibitor is like a cork in a bathtub preventing the water from flowing out.

Catalytic means that enzymes can significantly speed up reactions. For example, if you have a solution with two molecules that can potentially react with each other, the addition of the enzyme can speed up reaction from 108 to 1012 times compared to the usual rate.

Each type of enzyme works with only one type of reaction or molecule. For example, enzyme lactase breaks up lactose and cannot react with anything else.

Cofactors are non-protein molecules, often elementary (for example, zinc). Without them, the enzymes are unable to participate in reactions.

The ability of the enzyme to perform its function depends on its active site. The active site is formed by the residues of amino acids in such a way that it can bind to a molecule of a particular composition and shape. This mode of action is called the lock-and-key model.

• At present, there is another model that is called “induced fit model“. According to that idea, the enzyme reacts to the nearness of the correct molecule (called a substrate) and shapes its active site so the substrate would fit fully into it.
• The active site may have one or more “landing points” for molecules. This way, the enzyme can bring two molecules together so that they can react with each other.

If those molecules were just placed in the solution, they would react much slower. It happens for several reasons:

1. First of all, each reaction requires a certain amount of energy. When the enzyme binds to the molecules participating in the reaction, it also lowers the amount of energy that would be required.
2. During each reaction, the potential result product has to go through the so-called transition state. It is very unstable. However, when the molecules are bound to the enzyme, this transitional product is much more stable so that the reaction can go faster.
3. The enzyme also weakens the bonds between the components of the molecule, so that it can be broken up or new parts can be attached to it.

When the reaction is finished, the products no longer fit into the active site of the enzyme, so they are released. Another molecule can take its place, and the whole process can begin again.

Inhibitors that can block the enzymes have similar shapes to the “correct” molecules, but they bind to the active site in the slightly wrong way so that the specific activity of this particular protein (for example, ability to attach chemical groups) is blocked.

There are several types of enzymes:

• Helicases – can unwind DNA;
• Ligases – join two separate molecules;
• Oxido-reductases – facilitate the electron transfer;
• Hydrolases – add -OH groups;
• Transferases – move a group from one molecule to another;
• Lyases – split chemical bonds;
• Isomerases – create isomers – molecules with the same composition, but another orientation;

In the natural environment, enzymes are responsible for digestion and creation of new molecules (nucleic acids, lipids, and other proteins).

They can also modify and control the activity of other molecules. Humans also use enzymes in the industry (Example: Washing powders).