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Enzyme Definition

An enzyme is a protein that acts as a catalyst in living organisms, controlling the rate at which chemical reactions occur without itself being unaffected in the process. This article will discuss the complete overview of an enzyme, its types, structure, cofactors, and examples.

What is an enzyme?

Enzymes are biochemical polymers that catalyze biochemical reactions. An enzyme is a biological catalyst that always a protein. It accelerates the rate in the cell of a particular chemical reaction. The enzyme doesn't destroy during the reaction and may reuse them various times. There are several different types of enzyme molecules in a cell, each unique to a chemical reaction.

The metabolic process's initial stage depends on the enzymes and reacts with the molecule known as substrate. The substrates are converted into other distinct molecules by enzymes and are called products. The enzyme control has become a key component of clinical diagnosis because of its significance in maintaining life cycles. Proteins make up the macromolecular components of all enzymes, except ribozymes, which are RNA catalysts. The name ribozyme comes from the ribonucleic acid enzyme.

Structure of Enzyme

Enzymes are proteins that serve in cellular metabolism. They can affect catalyze reactions and may be used to reverse reactions in biochemical processes. While enzymes have complex enzyme structures, they undergo several necessary changes, so enzyme structure is critical. Each reaction requires a different enzyme.

Enzymes are composed of amino acids that are connected in a linear chain by amide bonds. It is the main structure. The resulting amino acid chain is known as protein and polypeptide. The DNA sequence of the corresponding gene encodes the basic order of amino acids in a polypeptide.

Types of Enzymes

There are mainly six types of enzymes that occur in the body by biochemical reactions. These are as follows:

  • Oxidoreductases
  • Lyases
  • Transferases
  • Hydrolases
  • Isomerases
  • Ligases


These enzymes contribute to reactions of oxidation and reduction and also known as oxidoreductases. These reactions move electrons in the type of hydride ions or hydrogen atoms. If a substrate is oxidized, these enzymes serve as hydrogen donors. These enzymes are called reductases or dehydrogenases. If the oxygen atom is the acceptor, all these enzymes are known as oxidases.


These enzymes catalyze reactions in which functional groups are added to molecules to break double bonds and where functional groups are removed form double bonds.


These enzymes catalyze the transition of a chemical group from one compound to the next.


Enzymes that catalyze reactions involving the hydrolysis process are known as hydrolases. They break single bonds by adding water. As they save the peptide bonds in proteins, some hydrolases act as digestive enzymes. Since they move the water molecule from one compound to another, hydrolases may be considered a transferase form. For instance, the enzyme pepsin hydrolyzes peptide bonds in the proteins.


These enzymes catalyze reactions. The functional group is moved to a different location within the same molecule, resulting in essentially an isomer of the original. For example, triosephosphate isomerase and phosphoglucose isomerase for the conversion of 6-phosphate glucose to 6-phosphate fructose.


The function of these enzymes is opposite to that of hydrolases. Ligases form a bond by removing the water element, while hydrolases break bonds by adding water. There are various subclasses of ligases that include ATP synthesis.

Cofactors in Enzymes

Cofactors are non-protein compounds associated with enzymes. A cofactor is needed for the proper functioning of an enzyme. An enzyme without a cofactor is recognized as an apoenzyme. A holoenzyme is a combination of an enzyme and its cofactor. In the enzyme, there are three types of cofactors:

  • Prosthetic Groups
  • Coenzyme
  • Metal ions

Prosthetic Groups

These cofactors are strongly bound with an enzyme all time. A fad is a prosthetic group that is available in several enzymes.


The coenzyme binds to the enzyme only during the catalysis process. For other times, it is separated from the enzyme. NAD+ is an example of a coenzyme.

Metal ions

For some enzyme catalysis, a metal ion is needed at the active site to form coordination bonds. Zn2+ is a cofactor of metal ions used by lots of enzymes.

What factors affect enzyme activity?

Various factors that affect the enzyme activity are as follows:


Each enzyme operates at its optimum temperature. Any change in temperature influences an enzyme's activity and causes denaturation.


The existence of certain substances obstructs the activity of a particular enzyme. It happens when the inhibitor is bound to the enzyme's active site, preventing the substrate's attachment and slowing down the process.


Enzymes are extremely sensitive to pH changes and can only operate within a very limited pH range. There's a risk that the enzymes will disintegrate if the pH is too low or too high, slowing down the reaction.

Mechanism of enzyme reaction

Any two molecules must collide for the reaction to happen, along with the proper orientation and an appropriate amount of energy. It is necessary for the energy between these molecules to pass the barrier in the reaction. This type of energy is known as activation energy. An active site is said to exist in enzymes. The active site for binding reactant molecules is a part of the molecule with a definite shape and functional group. The substrate group refers to the molecule which connects to the enzyme. When there are no catalysts present, the substrate and enzyme generate an intermediate reaction with reduced activation energy.

The basic mechanism is to catalyze chemical reactions that begin with the substrate binding to the enzyme's active site. This active site is a mixture of a substrate and a specific zone.

Examples of Enzymes

There are various examples of enzymes. Some of them are as follows:


Amylase is an enzyme that helps turn starches into sugars. It is present in human saliva and certain other mammals. It helps to digest foods, such as potatoes and rice, that contain large amounts of starch. The enzyme converts some of the starch into sugar, making it possible to feel a sweet taste when a person eats potatoes.


Lipase is found in all living organisms and is essential for the absorption, transport, and processing of dietary lipids, oils, and fats.


The small intestine has also been found to split lactose, sugar in milk, glucose, and galactose.


It is also found in saliva and breaks down sugars to form glucose in the pancreas.

Other Enzymes

Renin is used in cheese making. Cellulases and liginases help soften the paper. In fabric, softeners, proteases, lipases, and others are used. Catalase helps transform latex into rubber.

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