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Secondary Metabolites

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Plant Physiology, Development and Metabolism

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Abstract

Plants synthesize an enormous array of organic compounds/metabolites, a large number of which are involved in facilitating the basic vital processes, such as growth, cell division, respiration, photosynthesis, reproduction, and storage. These metabolites are known as primary metabolites, while the rest of the compounds do not have any role in primary metabolism. These compounds perform varied functions and are collectively referred as secondary metabolites. At biosynthetic level, both categories of compounds are synthesized from same basic metabolic pathways and share many intermediates (Fig. 33.1). Secondary metabolites are also referred as secondary products, specialized metabolites, or natural products. More than 2,00,000 secondary metabolites have been identified till now. Primary metabolites are generally produced in large concentrations as they are required in vital processes. However, secondary metabolites are mostly produced in small quantities, are structurally diverse, and may have a restricted distribution in specific families, genera, or species. Due to their confined, specific distribution, secondary metabolites can be used as a diagnostic tool in chemotaxonomic studies. For many years, the significance of secondary metabolites was not well understood, and they were believed to be mere metabolic wastes or functionless intermediates or end products of primary metabolism. Later, investigations initiated in the nineteenth century, pioneered by organic chemists, revealed the importance of secondary metabolites in medicines (e.g., discovery of aspirin (acetylsalicylate), as defensive compounds (phytoalexins), role in restricting germination and growth of other plants growing in the vicinity (allelopathy), UV protection, etc. Therefore, these metabolites help in adaptation of plants according to their environment. Some of their major roles are:

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Suggested Further Reading

  • Kutchan TM, Gershenzon J, Moller BL, Gang DR (2015) Natural products. In: Buchanan BB, Gruissem W, Jones RL (eds) Biochemistry and molecular biology of plants. Wiley Blackwell, London, pp 1132–1206

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Author information

Authors and Affiliations

  1. Department of Botany, University of Delhi, New Delhi, Delhi, India

    Satish C Bhatla

Authors
  1. Satish C Bhatla
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Multiple-Choice Questions

Multiple-Choice Questions

  1. 1.

    Phenolic compounds are produced by:

    1. (a)

      Plants and bacteria

    2. (b)

      Fungi

    3. (c)

      Algae and plants

    4. (d)

      Plants only

  2. 2.

    Association of phenols with various compounds such as proteins leads to the formation of new group of phenolic compounds, known as:

    1. (a)

      Polyphenols

    2. (b)

      Phenylpropanoids

    3. (c)

      Flavanoids

    4. (d)

      Stilbenes

  3. 3.

    Discoloration (browning) of apple after slicing or extended exposure to air occurs due to which of the following compounds?

    1. (a)

      Terpenoids

    2. (b)

      Alkaloids

    3. (c)

      Phenols

    4. (d)

      None of the above

  4. 4.

    Phenolic compounds are synthesized in plants via which of the following mechanism?

    1. (a)

      Shikimate/chorismate pathway

    2. (b)

      Acetate/malonate pathway

    3. (c)

      Acetate/mevalonate pathway

    4. (d)

      All of the above

  5. 5.

    The most abundant group of organic compounds in plants, after cellulose, is:

    1. a)

      Lignin

    2. b)

      Terpenes

    3. c)

      Alkaloids

    4. d)

      Flavanoids

  6. 6.

    Among the following, which describes the properties of flavanoids correctly?

    1. (a)

      Antiestrogenic, anticancerous, and antimicrobial

    2. (b)

      Anti-microbial and appetite suppressor

    3. (c)

      Mutagens and pigmentation in petals and bracts

    4. (d)

      Anticancerous, mutagens, and appetite suppressor

  7. 7.

    “Phytoalexins” produced by plants as a result of pathogen attack are:

    1. (a)

      Glycoproteins

    2. (b)

      Lipids

    3. (c)

      Phenolic compounds

    4. (d)

      Proteins

  8. 8.

    Which of the secondary metabolites listed below is a terpene?

    1. (a)

      Beta-carotene

    2. (b)

      Coumarins

    3. (c)

      Tannin

    4. (d)

      Glycosides

  9. 9.

    The first few compounds belonging to the category of terpenoids were isolated from?

    1. (a)

      Sunflower

    2. (b)

      Clove

    3. (c)

      Pine tree

    4. (d)

      Eucalyptus

  10. 10.

    Terpenes are ________ in nature, composed of ___ carbon units.

    1. (a)

      Lipophobic, five

    2. (b)

      Volatile, four

    3. (c)

      Lipophilic, five

    4. (d)

      Lipophobic, four

  11. 11.

    Condensation of isoprene units of 5-carbon leads to the formation of the terpenoids. In which of the terpenoids listed below are the carbon atoms not multiples of five?

    1. (a)

      Myrene

    2. (b)

      Carotenes

    3. (c)

      Tiglic acid

    4. (d)

      Steroids

  12. 12.

    The key enzyme in the mevalonic acid pathway (MVA) for the biosynthesis of terpenes is:

    1. (a)

      Isopentenyl diphosphatase

    2. (b)

      3-hydroxyl-3-methylglutaryl CoA (HMGR)

    3. (c)

      Phenyltransferase

    4. (d)

      1-deoxy-D-xylulose-5-phosphatase

  13. 13.

    Which of the following alkaloid is not a plant-derived alkaloid?

    1. (a)

      Caffeine

    2. (b)

      Colchicine

    3. (c)

      Bufotalin

    4. (d)

      Ajmaline

  14. 14.

    Which of the following groups of secondary metabolites is also known as proanthocyanidins?

    1. (a)

      Condensed tannins

    2. (b)

      Hydrolyzable tannins

    3. (c)

      Glycosides

    4. (d)

      None of the above

  15. 15.

    Which of the following is a synthetic antimalarial drug?

    1. (a)

      Quinine

    2. (b)

      Chloroquinone

    3. (c)

      Codeine

    4. (d)

      Heroin

  16. 16.

    First alkaloid to be isolated and characterized from plants is:

    1. (a)

      Caffeine

    2. (b)

      Morphine

    3. (c)

      Quinine

    4. (d)

      Cocaine

  17. 17.

    Which of the following is a characteristic of glycosides?

  1. (i)

    They comprise an aglycone and glycone moiety.

  2. (ii)

    Their synthesis involves the activity of glycosyltransferases.

  3. (iii)

    They are characterized by detergent-like properties.

    1. (a)

      Only i and ii

    2. (b)

      Only ii and iii

    3. (c)

      Only i and iii

    4. (d)

      All of the above

  1. 18.

    Anti-fungal activity of saponins is attributed to:

    1. (a)

      Hemolysis

    2. (b)

      Disruption of membrane

    3. (c)

      Coagulation of proteins

    4. (d)

      None of the above

  2. 19.

    Alkaloid with antineoplastic properties includes:

    1. (a)

      Vincristine

    2. (b)

      Morphine

    3. (c)

      Codeine

    4. (d)

      Nicotine

  3. 20.

    Which is not a cyanogenic glycoside?

    1. (a)

      Amygdalin

    2. (b)

      Lotaustralin

    3. (c)

      Gitalin

    4. (d)

      Linamarin

  4. 21.

    The cleavage of glucose from glucosinolate to form an aglycone entity is catalyzed by:

    1. (a)

      Glycosidase

    2. (b)

      Myrosinase

    3. (c)

      Hydroxynitrilase

    4. (d)

      Glucosidase

  5. 22.

    Amygdalin, a well-known cyanogenic glycoside, is isolated from:

    1. (a)

      Linseed

    2. (b)

      Bean

    3. (c)

      Cassava

    4. (d)

      Bitter almond

  6. 23.

    Which secondary metabolite is responsible for the pungent taste and smell of cruciferous vegetables?

    1. (a)

      Cardiac glycosides

    2. (b)

      Glucosinolates

    3. (c)

      Cyanogenic glycosides

    4. (d)

      Phenolics

  7. 24.

    Cyanogenic glycosides are so-called because under certain circumstances they give rise to:

    1. (a)

      Potassium cyanide

    2. (b)

      Sodium cyanide

    3. (c)

      Hydrogen cyanide

    4. (d)

      Both (a) and (b)

Answers

1.a

2.b

3.c

4.d

5.a

6.a

7.c

8.a

9.c

10.c

11.b

12.b

13.c

14.a

15.b

16.b

17.d

18.b

19.a

20. c

21. b

22. d

23. b

24. c

   

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Bhatla, S.C. (2018). Secondary Metabolites. In: Plant Physiology, Development and Metabolism. Springer, Singapore. https://doi.org/10.1007/978-981-13-2023-1_33

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