Glucosinolate Biosynthesis and Structure
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Questions and Answers

Which mustard contains sinigrin, which breaks down into potassium hydrogen sulfate, glucose, and allyl isothiocyanate upon hydrolysis?

  • White mustard
  • Cabbage
  • Black mustard (correct)
  • Lepidium sativum

    • Which enzyme is responsible for the hydrolysis of sinalbin into glucose and acrinylisothiocyanate?

  • Urease
  • Myrosinase (correct)
  • Hydrolase
  • Catalase

    • Which amino acid is the precursor for the biosynthesis of sinalbin?

  • Tyrosine (correct)
  • Homomethionine
  • Methionine
  • Leucine

    • To isolate glucosinolates, which substance is used to destroy the enzymes during extraction?

    <p>Boiling alcohol</p> Signup and view all the answers

    What compound induces cell cycle arrest and apoptosis in cancer cells when glucotropaeolin is hydrolyzed?

    <p>Benzyl isothiocyanate</p> Signup and view all the answers

    Which glucosinolate component has a protective effect against colon cancer?

    <p>Glucosinolates from cabbage</p> Signup and view all the answers

    Glucosinolate toxicity in animals such as sheep and cows leads to which condition?

    <p>Hypothyroidism</p> Signup and view all the answers

    What effect does sinigrin have on nitric oxide production?

    <p>Suppresses NO production</p> Signup and view all the answers

    What is the structural characteristic of Turkish galls hydrolysable tannin?

    <p>Glucose + 9-10 gallic acid residues</p> Signup and view all the answers

    What is the precursor molecule of ellagic acid?

    <p>Hexahydroxy-diphenic acid</p> Signup and view all the answers

    What is the characteristic property of condensed tannins?

    <p>They yield catechol on dry distillation</p> Signup and view all the answers

    What is the product of polymerization of condensed tannins?

    <p>Phlobaphenes</p> Signup and view all the answers

    Which type of tannin is structurally related to flavonoids?

    <p>Condensed tannin</p> Signup and view all the answers

    What is the characteristic color of phlobaphenes?

    <p>Red or brown</p> Signup and view all the answers

    What is the characteristic property of gallotannins?

    <p>They are hydrolyzed to gallic acid</p> Signup and view all the answers

    Which plant part is known to contain ellagitannins?

    <p>Eucalyptus leaves</p> Signup and view all the answers

    What is the source of tannic acid?

    <p>From galls, produced from various species of Quercus, F.Fagaceae</p> Signup and view all the answers

    What is the effect of condensed tannins on free radicals?

    <p>They serve as effective free radical scavengers</p> Signup and view all the answers

    What is the product of hydrolysis of tannic acid?

    <p>Gallic acid + Glucose</p> Signup and view all the answers

    What is the effect of tannins on enzyme systems?

    <p>They inhibit many enzyme systems</p> Signup and view all the answers

    What is the medical application of tannins in the treatment of burns?

    <p>As an antiseptic to prevent infection</p> Signup and view all the answers

    What is the effect of tannins on peripheral circulation?

    <p>They improve conditions of peripheral circulation</p> Signup and view all the answers

    What is a characteristic of hydrolysable tannins?

    <p>They can be hydrolyzed by acids or enzymes</p> Signup and view all the answers

    What is the primary function of tannins in the tanning industry?

    <p>To split off the sugar moiety from leather</p> Signup and view all the answers

    What is the difference between hydrolysable and condensed tannins?

    <p>Hydrolysable tannins can be broken down by acids or enzymes, while condensed tannins cannot</p> Signup and view all the answers

    What is the name of the test used to detect tannins?

    <p>Goldbeater's skin test</p> Signup and view all the answers

    What is the result of adding bromine solution to a condensed tannin?

    <p>A precipitate forms</p> Signup and view all the answers

    What is the function of phlobaphenes in plant extracts?

    <p>To inhibit crystallization</p> Signup and view all the answers

    What is the name of the type of tannin found in Chinese galls and Turkish galls?

    <p>Gallitannin</p> Signup and view all the answers

    What is the result of dry distillation of hydrolysable tannins?

    <p>Pyrogallol forms</p> Signup and view all the answers

    Study Notes

    Thioglycosides (Glucosinolate)

    • Contain Sulphur
    • Examples: Sinigrin (in black mustard) and Sinalbin (in white mustard)

    Reactions

    • Sinigrin (K myronate) on hydrolysis → KHSO4, glucose, and AITC (S=C=N-CH2-CH=CH2)
    • Sinalbin on enzymatic hydrolysis (Myrosin) → glucose, acrinylisothiocyanate

    Structure

    • Glucosinolates consist of a glucose residue, a sulfate group, and a variable aglycone, occurring as a potassium salt

    Biosynthesis

    • Tyrosine → Sinalbin
    • Homomethionine → Sinigrin

    Extraction and Quantitation

    • Destroying enzymes with boiling alcohol allows for isolation of glucosinolates
    • Anionic resin separates glucosinolates due to their ionic nature
    • Quantitation involves condensation of isothiocyanate with 1,2-benzene dithiol → 1,3-benzodithiol-2-thione, measured by spectrophotometry

    Glucosinolate Toxicity

    • Ingestion of large amounts of glucosinolate-containing plants (e.g., cabbages) by animals (e.g., sheep, rabbits, cows) can cause Hypothyrodism

    Glucosinolate Potential

    • Glucosinolates are beneficial to human health
    • Dietary intake of glucosinolates (from cabbage and cauliflower) may have a protective effect against colon cancer

    Glucosinolate Containing Drugs

    • Sinigrin (from black mustard seeds) suppresses NO (Nitric oxide) production, having an anti-oxidant effect in vivo
    • Sinalbin (from white mustard seeds) may cause apoptosis (pre-cancerous cell death), preventing colon cancer when consumed regularly
    • Glucotropaeolin (from Lepidium sativum) releases benzyl isothiocyanate (BITC), inducing cell cycle arrest and apoptosis in cancer cells

    Types of Tannins

    • Hydrolysable Tannins:
      • Contain glucose and gallic acid residues
      • Found in Chinese galls, Turkish galls, Hamamelis, and Rhubarb
      • Can be hydrolyzed to yield gallic acid and glucose
    • Condensed Tannins (Catechol Tannins):
      • Structurally related to flavonoids
      • No sugar in their molecule
      • On dry distillation, yield catechol
      • Solutions turn green with ferric chloride
      • Polymerize in acid solutions or with oxidative agents, forming phlobaphenes

    Characteristics of Tannins

    • Precipitate proteins (e.g., gelatin) and make them resistant to proteolytic enzymes
    • Form cross-links with proteins and other macromolecules
    • Detected qualitatively by the goldbeater's skin test
    • Determined quantitatively by absorption on standard hide powder
    • React with FeCl3 to produce a bluish-black color (hydrolysable tannins) or greenish-black color (condensed tannins)

    Classification of Tannins

    • According to Goldbeater's skin test:
      • True tannins: positive tanning test
      • Pseudo-tannins: negative tanning test
    • According to structure:
      • Hydrolysable tannins (pyrogallol tannins)
      • Condensed tannins (catechol tannins)

    Hydrolysable Tannins

    • Consist of a polyhydric alcohol (mostly glucose) esterified with a phenolic acid (gallic acid, hexahydroxy diphenic acid, or ellagic acid)
    • Can be hydrolyzed by acids or enzymes, yielding carbohydrate and crystalline phenolic acids
    • On dry distillation, yield pyrogallol
    • Examples:
      • Gallitannins (Chinese galls, Turkish galls, Hamamelis, red rose petals, rhubarb, and clove)
      • Ellagitannins (pomegranate rind and bark, eucalyptus leaves, and oak bark)

    Medicinal Properties of Tannins

    • Anti-diarrheal
    • Haemostatic (stops bleeding)
    • Treats hemorrhoids
    • Antidote for heavy metal toxicity
    • Treats burns, GIT ulcers, bed sores, inflammation, and serves as an antiseptic
    • Antioxidant properties: condensed tannins serve as effective free radical scavengers
    • Improves peripheral circulation, capillary fragility, and inflamed collagen disease
    • Inhibits enzyme systems:
      • 5-lipooxygenase (anti-inflammatory effect)
      • Angiotensin-converting enzyme (treatment of hypertension)
      • Topoisomerases and protein kinase C (treatment of cancer)

    Tannic Acid

    • Source: from galls of various Quercus species (Fagaceae)
    • Structure: hydrolysable tannin
    • On hydrolysis, yields gallic acid and glucose
    • Test: gives a bluish-black color with FeCl3

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    Description

    Learn about glucosinolates, their structure, and biosynthesis from tyrosine and homomethionine into sinigrin and sinalbin, important compounds found in mustard.

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