Primary Metabolites vs. Secondary Metabolites

Metabolites are the microbial products, which are the low molecular weight compound, necessary for the cell’s or body metabolism processes. These products are categorized as primary and secondary metabolites. The microorganisms possess a tremendous capacity to synthesize different products that are also commercially used.

The metabolites which are essentially required for the growth and maintenance of the cellular function are called primary metabolites. In contrast, the metabolites which are not needed for the growth and maintenance of the cellular functions and are produced as the products of the central metabolism are called secondary metabolites.

Comparison Table

Basis for ComparisonPrimary MetabolitesSecondary Metabolites
DefinitionA primary metabolite is a type of metabolite that is directly involved in normal growth, development, and reproduction.A secondary metabolite is the organic compound produced by the bacteria, fungi, or plant and is not directly involved in the normal growth, development, or reproduction.
PhaseGrowth phaseStationary phase
Another nameTropophaseIdiophase
Quantity of productionLarge amountSmall amount
Extraction processEasyDifficult
OccurrenceSame in every speciesVaries in different species
ExamplesCarbohydrates, proteins, lipids and vitaminsSteroids, essential oils, phenolics, alkaloids

What are Primary Metabolites?

Primary metabolites are the compounds produced during the exponential growth phase. The process is called tropopause or primary metabolism. This process of growth is started when all the required nutrients are present in the medium for an organism to grow. Primary metabolites are used by the cell as the building blocks of the essential macromolecules. So, the importance of the primary metabolism is in the cell’s growth, reproduction, and development. In this phase, the cell has a minimum concentration of all the molecules.

Types of Primary Metabolites

The primary metabolites are divided into two categories; primary essential metabolites and primary metabolic end products.

Primary Essential Metabolites: These are the important primary metabolites required to sustain the process of cell growth. Hence, these are produced in sufficient quantity. Amino acids, vitamins, nucleosides are examples of essential metabolites.

Primary Metabolic End Products: These types of primary metabolites are the end products of primary metabolism. Ethanol, acetone, lactic acid and butanol are the normal end products of the fermentation process of primary metabolism. These products have industrial importance. For instance, carbon dioxide is the metabolic end product of the Saccharomyces cerevisiae. Carbon dioxide is important in the baking industry for the leavening of the dough.


The human body requires excessive production of the primary metabolites. Primary metabolites are also useful in the large scale purposes in industry. Enzymes are which are primary metabolites that have many uses in food production, textile finishing and other industries. Ethanol, lactic acid and a few amino acids are examples of primary metabolites.

In industrial microbiology, ethanol is one of the most common primary metabolites which is used for large-scale production. Ethanol is used for fermentation, which produces products such as beer and wine. Amino acids (L-glutamate, L-lysine_, which are used as supplements, are isolated through mass production of a specific bacterial species, Corynebacteria glutamicum. Citric acid is also an example of primary metabolites. It is produced by Aspergillus niger and is used widely in food production. It is also used in the pharmaceutical and cosmetic industries as well.

What are Secondary Metabolites?

Secondary metabolites are the derivatives of primary metabolites. At the last of the exponential phase, the process enters into another phase called idiophase or secondary metabolism. The products which are produced at the end of this phase, are called secondary metabolites. This phase happens when nutrients are limited or accumulation of waste products.

Secondary metabolites accumulate in small quantities in specific parts of the plants. By the cultivation of the plant’s cells in the culture media, secondary metabolites can be produced on a large scale.

Antibiotics, alkaloids, steroids, toxins and gibberellins are examples of secondary metabolites. These products do not have a direct role in the synthesis of cell materials and growth but are required in small quantities.

Types of Secondary Metabolites

Secondary metabolites are numerous in number and chemically diverse. These metabolites are of three categories; isoprenoids or terpenes nitrogen-containing compounds and phenolic compounds. Rubber, steroids, essential oils and carotenoid pigments are examples of isoprenoids. Alkaloids, glycosides, glucosinolates and non-protein amino acids are examples of nitrogen-containing compounds, whereas lignin, tannins, coumarins, aflatoxins and flavonoids are phenolic compounds.


Secondary metabolites do not perform a direct role in cell growth and development. But they perform some unknown functions which support cell survival.

Atropine and antibiotics (erythromycin and bacitracin) are examples of the secondary metabolites of industrial microbiology. Atropine has been derived from various plants and used for different medical purposes. It is a competitive antagonist for acetylcholine receptors and is used in the treatment of bradycardia.

Erythromycin and bacitracin are also considered to be secondary metabolites. Erythromycin has been derived from Saccharopolyspora erythraea and has a wide antimicrobial spectrum. It is produced in massive amounts and used orally. Similarly, bacitracin is an antibiotic that is a topical drug and clinically used for different treatments.

Key Differences between Primary Metabolites and Secondary Metabolites

  1. The primary metabolites are the products that are produced during the growth phase of the organisms, whereas secondary metabolites are derived from the pathways of the primary metabolites.
  2. The primary metabolites are involved in the growth and development of an organism, whereas secondary metabolites are included in the stationary phase during the growth of a microorganism.
  3. The primary metabolism pathway occurs at the growth phase known as tropopause whereas the secondary metabolism pathway occurs at the stationary phase known as idiophase.
  4. Primary metabolites are part of the basic molecular structure of the cell, whereas secondary metabolite is not part of the basic molecular structure of the cell.
  5. Primary metabolites are produced in large quantities with an easy extraction process, whereas secondary metabolites are produced in small quantities with a difficult extraction process.
  6. The products of the primary metabolites are produced the same in all species, whereas the products of the secondary metabolites are different for different species.
  7. Primary metabolites perform different significant functions in the plants, whereas secondary metabolites have a limited role in the plants.
  8. Examples of the primary products are carbohydrates, proteins, vitamins and lipids, whereas the examples of the secondary metabolites are phenolics, steroids, essential oils, and alkaloids.


In conclusion, both primary and secondary metabolites are the types of metabolites that are involved in cell growth. But they differ from each other in certain aspects. Primary metabolites are involved in cell growth directly, whereas secondary metabolites are involved in cell growth indirectly.

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