12 differences between Primary and Secondary Metabolites

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Last Updated on August 18, 2020 by Sagar Aryal

Differences between Primary Metabolites & Secondary Metabolites
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Primary Metabolites Definition

  • Primary metabolites are the compounds that are directly involved in the metabolic pathways of an organism necessary for its growth, development, and reproduction.
  • These metabolites are associated with the physiological processes occurring in the organism.
  • Primary metabolites are produced in the organism during the growth phase, as a result of the growth mechanism.
  • The growth phase associated with the production of primary metabolites is termed as ‘trophophase’.
  • The production of primary metabolites is initiated when the nutrients necessary for the body are available in the medium.
  • These are found in most cells throughout the body and are also termed central metabolites.
  • Primary metabolites are crucial for various metabolic activities as some act as a substrate for these processes, while others act as catalysts.
  • Some primary metabolites like amino acids are common throughout the organisms, whereas some are restricted to some cells or some organisms.
  • Even though primary metabolites play an essential role in the growth and development of an individual, these do not have pharmacological actions or effects against other factors.
  • The production of primary metabolites usually occurs at a high rate as these are constantly required for the body. These can also be extracted easily through simple extraction procedures.
  • Primary metabolites are divided into two groups; primary essential metabolites and primary metabolic end products.
  • Primary essential metabolites include compounds like proteins and carbohydrates that make up the structural and physiological organization of the organism. In contrast, primary metabolic end products include products like lactic acid and ethanol that are the end products of various metabolic pathways.
  • Examples of primary metabolites include proteins, enzymes, carbohydrates, lipids, vitamins, ethanol, lactic acid, butanol, etc.

Secondary Metabolites Definition

  • Secondary metabolites are the organic compounds that are produced by various organisms that are not directly involved in the growth, development, or reproduction of the organism but are essential in the ecological and other activities.
  • Secondary metabolites are also termed specialized metabolites or natural products.
  • Because secondary metabolites are not involved in the growth and development of the organism, the absence of these compounds causes little to no effect on the survivability of the organism.
  • However, in the long run, some mild effects might be observed.
  • Some secondary metabolites are specific to a species and are only found in them, but the horizontal transfer of these metabolites across species has seen to play an important role in the evolution of some organisms.
  • Although they are not important for survival, secondary metabolites might be important for other activities like protection, competition, and species interaction.
  • Secondary metabolites are classified into groups based on their biosynthetic origin. Some of the secondary metabolites are derived forms of primary metabolites.
  • These are also formed during the stationary phase of growth in most organisms. This phase of growth is termed ‘idiophase’.
  • Most secondary metabolites tend to act as a defense mechanism against various foreign invaders.
  • These are produced in rather smaller quantities and are difficult to extract.
  • Secondary metabolites are also not a part of the molecular organization of the organism.
  • Some categories of secondary metabolites have been used in various biotechnological procedures for the formation of drugs and other compounds.
  • Since secondary metabolites are specific to species, different secondary metabolites are involved in various procedures.
  • Some examples of secondary metabolites include steroids, essential oils, phenolics, alkaloids, pigments, antibiotics, etc.

Key differences (Primary Metabolites vs Secondary Metabolites)

Basis for Comparison

Primary Metabolites

Secondary Metabolites

DefinitionPrimary metabolites are the compounds that are directly involved in the metabolic pathways of an organism necessary for its growth, development, and reproduction.Secondary metabolites are the organic compounds that are produced by various organisms that are not directly involved in the growth, development, or reproduction of the organism but are essential in the ecological and other activities.
Also termedPrimary metabolites are also termed as central metabolites.Secondary metabolites are also termed as specialized metabolites.
Growth phasePrimary metabolites are produced during the growth phase of the organism.Secondary metabolites are produced during the stationary phase of the organism.
This phase of growth is also termed as ‘trophophase’.This phase of growth is also termed as ‘idiophase’.
QuantityPrimary metabolites are produced in large quantities.Secondary metabolites are produced in small quantities.
ExtractionIt is easier to extract primary metabolites.It is difficult to extract secondary metabolites.
SpecificityPrimary metabolites are not species-specific and thus might be identical in some organisms.Secondary metabolites are species-specific and thus are different in different organisms.
Involved inPrimary metabolites are involved in the growth, development, and reproduction of organisms.Secondary metabolites are involved in ecological functions and species interactions.
Structural componentPrimary metabolites might form the molecular structure in organisms.Secondary metabolites are not a part of the molecular structure of the organism
ImportancePrimary metabolites are used in various industries for different purposes.Secondary metabolites are used in various biotechnological procedures for the formation of drugs and other compounds.
Defensive actionPrimary metabolites are not active in the defense mechanism.Secondary metabolites are active against foreign invaders and might be involved as a defense mechanism.
ExamplesExamples of primary metabolites include proteins, enzymes, carbohydrates, lipids, vitamins, ethanol, lactic acid, butanol, etc.Some examples of secondary metabolites include steroids, essential oils, phenolics, alkaloids, pigments, antibiotics, etc.

Examples of primary metabolites

Enzymes

  • Enzymes are proteins that are produced in the body of different organisms as primary metabolites.
  • Enzymes are important compounds that catalyze various metabolic pathways throughout the body.
  • Enzymes are proteins formed of polypeptide chains of amino acids that are highly specific for the reaction they catalyze.
  • In the absence of enzymes, the biological reactions would require a long period of time to complete.
  • Enzymes are conservative and do not get spent during chemical reactions.
  • These are involved in almost all forms of metabolic pathways ranging from cellular respiration to internal digestion and absorption.
  • The enzymes produced in various organisms are extracted for their use in industries for processes like fermenting of wine, the leavening of bread, curdling of cheese, and brewing of beer.
  • Some examples of enzymes include lipases, amylases, proteases, etc.

Carbohydrates

  • Carbohydrate is a group of organic compounds that play an important role in the structural and physiological components of all living beings.
  • Carbohydrates are among the most important primary metabolites that are common in all living organisms.
  • A carbohydrate is a biomolecule formed of carbon, hydrogen, and oxygen. These provide structure to organisms like cellulose in plants and peptidoglycan in bacteria.
  • Besides, these are also compounds that are oxidized to obtain energy for the growth and functioning of the organism.
  • Carbohydrates are of various types depending on their length and composition. They are also divided based on their functions.
  • Carbohydrates act as substrates for the important biological processes like Kreb’s cycle and glycolysis.
  • Monosaccharides are also involved in the formation of macromolecules and might even function as reservoirs of energy and fats.
  • Some examples of carbohydrates include glucose, cellulose, glycogen, chitin, peptidoglycan, etc.

Examples of secondary metabolites

Pigments

  • Pigments are compounds of various colors that are produced by various organisms for various purposes.
  • These are secondary metabolites and are produced by various organisms like plants and bacteria.
  • Plant pigments like chlorophyll are essential for processes like photosynthesis, whereas bacterial pigments can be extracted to be used in industries as dyes.
  • Pigments are mostly non-toxic and might even have medicinal importance to be used as antioxidants and additives.
  • Bacterial pigments produced for industrial purposes by microbial fermentation has several advantages such as cheaper production, easier extraction, higher yields through strain improvement, no lack of raw materials, and no seasonal.
  • Biopigments produced from microorganisms are preferred over those from plants because of their stability and availability for cultivation throughout the year.
  • Examples of these pigments include chlorophyll, astaxanthin, zeaxanthin, indigoidine, rhodopsin, etc.

Flavonoids

  • Flavonoids are secondary metabolites in plants that are found in all fruits and vegetables.
  • Flavonoids are phytonutrients, meaning plant chemical, that also provides some coloration to many plants and animals.
  • These are the largest groups of phytonutrients found in plants with more than 6000 types known.
  • These compounds have important antioxidants with anti-inflammatory and immune system benefits.
  • They also have antimicrobials, photoreceptors, visual attractors, feeding repellants, and for light screening functions.
  • Flavonoids are known to control the development of individual organs and the whole-plant; and, hence, contribute to stress-induced morphogenic responses of plants.
  • Flavonoids may play critical roles as signaling molecules in mammals, through their ability to interact with a wide range of protein kinases.
  • Some examples of flavonoids found in various vascular plants include Apigenin, Luteolin, Hesperetin, Genistein, etc.

References and Sources

  • Brunetti, C., Di Ferdinando, M., Fini, A., Pollastri, S., & Tattini, M. (2013). Flavonoids as antioxidants and developmental regulators: relative significance in plants and humans. International journal of molecular sciences14(2), 3540–3555. https://doi.org/10.3390/ijms14023540
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