Enzymes: Its Structure, and Characteristics


Enzymes are biological catalysts. The main feature of enzymes is that they have biologically active proteins that can accelerate chemical reactions in cells, but they will not alter the reactions. As proteins, they are always bound in chains of amino acids with specific shapes and bonds.


Enzymes can increase the efficiency of biological reactions. They are specific to each type of response. Without enzymes, the reaction proceeds at a very slow rate. Therefore, it is impossible without an enzyme.

Structure of Enzyme

Enzyme have the following components:

Globular Structure

Enzymes are made up of hundreds of amino acids. These amino acids combine together to form a spherical structure.

Active Site

The catalytic activity is limited to a small part of the enzyme called the active site. It is made up of some amino acids. All other amino acids form the spherical structure of the enzyme. This active site participates in catalytic activity. These reagents are called substrates. The substrate is attached to the active site.

The active site of an enzyme consists of two regions:

  1. Binding site: It recognizes a specific substrate and forms an enzyme-substrate complex. This reaction activates the catalytic site.
  2. Catalytic site: The active catalytic site transforms the substrate into a product.


Some enzymes have non-protein parts called cofactors. Cofactors are essential for the normal function of these enzymes. Cofactors are essential for the normal function of these enzymes.

Cofactors act as a bridge between the enzyme and the substrate. They are often directly involved in chemical reactions. Sometimes, cofactors provide a source of chemical energy. This energy is necessary to initiate a reaction. There are three supporting factors:

  1. Activator: The detachable cofactor is called an activator. These cofactors are inorganic ions, such as Mg + 2, Fe + 2, Cu + 2
  2. Prosthetic group: The non-protein portion of the covalent is called a covalently bonded prosthetic group.
  3. Coenzyme: The non-protein portion that is loosely attached to an enzyme is called a coenzyme. Coenzymes are organic in nature but not protein. They are related to vitamins. Vitamins are the raw material for the synthesis of coenzyme. The coenzyme will not be destroyed during the reaction. Therefore, they can be used repeatedly. Therefore, less amount of vitamin is required in cells.


Enzymes with removed coenzyme or synthetic groups are called apoenzymes. Epoenzyme is still inactive.


The active enzyme composed of polypeptide chains and cofactors is called Holoenzyme. When cofactors combine with apoenzymes, holoenzyme are formed. This activates the enzyme and initiates the reaction.

Characteristics of Enzymes

Enzymes are biological catalysts. They have the following characteristics:

  • All enzymes are globular proteins.
  • They increase reaction speed. But they were not used in response.
  • They do not change the nature or characteristics of the final product.
  • A small amount of the enzyme can act on a large number of substrate molecules.
  • The role of enzymes is very specific. A single enzyme catalyzes only one substrate or a group of related substrates.
  • They are sensitive to changes in pH, temperature, and substrate concentration.
  • Some enzymes require cofactors to perform their normal functions.
  • They reduce the activation energy. The minimum energy required to initiate a reaction is called the activation energy.
  • If some enzymes are activated in the wrong place, they can cause damage. For example, pepsin is a protein digestive enzyme. It can destroy the internal structure of cells. Therefore, it is produced in an inactive form known as pepsinogen. Enzymes are formed in cells and attach to lysosomes. Lysosomes are membrane-bound bodies.
  • They are not consumed in the chemical process. After processing, they dissociate and can be used again.
  • In some enzymes, there is also a non-protein part called a prosthetic group.
  • Enzymes are used in specific chemical reactions. Not all reactions use every enzyme.
  • Due to the presence of proteins, they can react with acidic and alkaline substances.
  • Some ions or salts may activate enzyme activity. These ions or salts are called activators, such as Ni, Mn, Mg, and Cl. They reduce the activation energy.

Mechanism Of Enzyme Action

In most chemical reactions, the energy barrier must be overcome to react. This inhibition prevents the spontaneous degradation of complex molecules (such as proteins and nucleic acids), so protecting life is essential. However, when cells require metabolic changes, they must break down some complex molecules, and overcome this energy barrier. Heat may provide additional required energy (called activation energy), but rising temperatures will kill the battery. The alternative is to reduce the activation energy level using a catalyst. This is the role of the enzyme. They react with the substrate to form an intermediate complex (“transition state”), requiring less energy to react. Volatile intermediate compounds quickly decompose to form reaction products, and unchanged enzymes can freely react with other substrate molecules.

Only a certain region of the enzyme (called the active site) binds the substrate. The active site is the groove or pocket formed by the folding pattern of the protein. This three-dimensional structure and the chemical and electrical properties of amino acids and cofactors in the active site allow only specific substrates to bind to the site, thus determining the specificity of the enzyme.

Mechanism Of Enzyme Action

Factors Affecting Enzyme Activity

Since the enzyme is not consumed in the catalytic reaction, it can be used repeatedly, so only a very small amount of enzyme is required to catalyze the reaction. A specific enzyme molecule can convert up to 1,000 substrate molecules per second. The rate of the enzymatic reaction increases with the increase of substrate concentration, and the maximum rate is reached when all active sites of enzyme molecules participate. The enzyme is then called saturated, and the reaction rate is determined by the rate at which the active site converts the substrate into a product.

Enzyme activity can be inhibited in various ways. Competitive inhibition occurs when a molecule that is similar to a substrate molecule attaches to the active site and protects the actual substrate from bonding. For example, penicillin is a competitive inhibitor that blocks the active sites of enzymes that many bacteria use to build their cell walls.

When the inhibitor binds the enzyme at a location other than the active site, non-competitive inhibition occurs. In some cases of non-competitive inhibition, it is believed that the inhibitor binds to the enzyme in some way, thereby physically blocking the normal active site. In other cases, it is believed that the binding of the inhibitor changes the shape of the enzyme molecule, impairing its active site and preventing it from reacting with the substrate. The latter non-competitive prohibition is called all steric prohibition. The place where the inhibitor binds to the enzyme is called the allosteric site. Generally, the end product of a metabolic pathway acts as an allosteric inhibitor on the initial enzymes of the pathway. The inhibition of enzyme pathway products on the enzyme is a form of negative reaction.

Allosteric control can include stimulatory effects as well as inhibitory effects. The activator molecule can bind to the allosteric site and produce a reaction at the active site by changing its shape to adapt to the substrate that cannot induce transformation by itself. Common functional include hormones and products of early enzymatic reactions. All steric excitation and inhibition cells produce energy and substances when needed, and inhibit the production of energy and substances when supplies are sufficient.

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