Enzymes – The Biocatalyst [Structure, Coenzyme, Characteristics of Enzymes]

Enzymes – The Biocatalyst

Enzymes are the most important group of proteins that are biologically active. They greatly increase the efficiency of biochemical response and are specific for each type of reaction. Without these enzymes, the reaction would continue at a very sluggish speed making life difficult.

Structure of Enzymes

Enzymes are made up of hundreds of amino acids collaborated and coiled upon themselves to form a globular structure. The catalytic activity is limited to a small portion of the structure called the active site. The reactant called substrate is connected to the active site including only a few amino acids, while the rest of the bulk of the amino acids maintains the globular structure of the enzyme.



Some enzymes consist exclusively of proteins. Others also have a non-protein part, which is essential for the proper functioning of the enzymes. This non-protein part is called the co-factor.

Function of co-factor

The cofactor usually serves as a “bridge” in between the enzyme and its substrate, often it contributes straight to the chemical reactions which bring about catalysis. Sometimes the co-factor offers a source of chemical energy, assisting to drive reactions that would otherwise be difficult or impossible.


Some enzymes utilize metal ions as co-factors like Mg2+, Fe2+, Cu2+, Zn2+, etc. The separable co-factor is known as an activator if it is an inorganic ion.

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Prosthetic group

f the non-protein part is covalently bonded, it is known as a prosthetic group. Examples: thiamine pyrophosphate, pyridoxal-phosphate, and biotin.


If it is loosely attached to the protein part, it is called a coenzyme. Examples: nicotinamide adenine dinucleotide (NAD), nicotine amide adenine dinucleotide phosphate (NADP), and flavin adenine dinucleotide (FAD).

Apoenzyme and Holoenzyme

An enzyme with its coenzyme, or prosthetic group, eliminated is designated as apoenzyme. Adding the properly concentrated coenzyme to the apoenzyme will bring back enzyme activity. A triggered enzyme including a polypeptide chain and a cofactor is called a holoenzyme.

Presence of Enzymes

Numerous enzymes are just dissolved in the cytoplasm. Other enzymes are firmly bound to certain subcellular organelles. They are produced by living cells for use in or near the site of their production. The enzymes essential in photosynthesis are discovered in the chloroplasts and enzymes involved in cellular respiration are found in the mitochondria. Some of the enzymes which are associated with the synthesis of proteins are an essential part of ribosomes.

A lot of enzymes do not float about in a sort of cytoplasmic soup’ but are connected to membrane systems inside the cell in specific and organized arrangements.

Mitochondria and chloroplasts are good examples of this.

Characteristics of Enzymes

Enzymes, the biochemical catalysts possess the following important attributes.

  1. All enzymes are globular proteins.
  2. They increase the rate of a reaction without themselves being consumed.
  3. Their existence does not affect the nature or properties of the final product.
  4. Percentages of an enzyme can speed up chain reactions.
  5. They are extremely specific in their action; a single enzyme catalyzes just a single chemical reaction or a group of associated reactions.
  6. They are sensitive to even a minor change in pH, temperature level, and substrate concentration.
  7. Some enzymes require a co-factor for their proper performance.
  8. They lower the activation energy of the reactions.
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Mechanism of Enzyme Action

An enzyme is a 3-dimensional globular protein that has specific chemical composition due to its element amino acids and a specific shape. Every enzyme by virtue of its specificity acknowledges and reacts with a unique chemical compound called the substrate. Any enzyme, therefore, responds only with its specific substrate and transforms it into product(s). It is then released unaltered and therefore can be used again and again.

E      +        S                              ES                                            E          +          P

Enzyme    Substrate          Enzyme Substrate Complex           Enzyme      Product

In specific cases, enzymes act in a series of chain reactions in a specific order to complete a metabolic path such as respiration or photosynthesis. The succeeding enzymes including these reactions are usually present together in a precise order of reaction such that substrate molecules can be literally handed on from one enzyme to another forming an enzyme to enzyme chain. In this way, the products from one step in the pathway are moved to the enzyme catalysing the next action.


An enzyme and its substrate react with each other through a definite charge-bearing site of an enzyme called the active site. The charge and shape of the active site are formed by some amino acids present in the polypeptide chain of the active site of the enzyme. These amino acids are brought more detailed and are set up in a particular way by coiling and folding of the polypeptide chain within the globular symmetry of the enzyme.

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The active website of the enzyme is comprised of 2 definite regions i.e. the binding site and the catalytic site. The binding site helps the enzyme in the recognition and binding of a proper substrate to produce an ES complex. This reaction triggers the catalytic site. Catalytic site catalyzes the change of the substrate into product(s). Hence the enzyme after catalysis removes itself from the products unchanged. The enzyme requires liquid medium for its activity.


An enzyme is a biological catalyst that can accelerate a specific chemical reaction by lowering the activation energy but remain unaltered in the reaction. Most enzymes are protein but some are nucleic acids like ribozymes.

Enzymes have enormous catalytic power. They greatly increase the rate at which chemical reactions take place. These are three-dimensional globular molecules. It has at least one surface region. This region has crevice. This crevice is known as the enzyme’s active site.

The substrate molecule fits into it in a very specific way. The metal ions loosely attached to enzymes are cofactors. These are required for the proper functioning of enzymes.

Coenzymes are non-protein, organic molecules that participate in enzyme-catalyzed reaction. Many vitamins like niacin and riboflavin function as coenzymes. Coenzymes transport energy in the form of hydrogen atoms from one enzyme to another.