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Questions and Answers
What is the primary role of the glycone part of a glycoside in the body?
Which type of glycoside bond connects the sugar to the aglycone through oxygen?
In which condition do glycosides predominantly exist within plants?
What characterizes the chemical nature of glycosides compared to sugars?
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Which type of glycoside is characterized by a sugar attached through a carbon-carbon bond?
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What is a distinguishing feature of the aglycone part of glycosides?
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How do the solubility properties of glycosides differ from those of their aglycones?
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What does hydrolytic cleavage of glycosides yield?
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What is the primary method for hydrolyzing glycosides?
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Which enzyme is primarily responsible for hydrolyzing most β-glycosidic linkages?
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Which of the following statements regarding the stability of glycosides is correct?
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What role do glycosides play in plants?
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Which classification criterion for glycosides is primarily based on the sugar structure?
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Which of the following glycosides is known for yielding a powerful local irritant?
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How do α and β stereo-isomers of glycosides differ in terms of enzyme hydrolysis?
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Which characteristic is common for most glycosides?
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What is the characteristic feature of C-glycosides?
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Which of the following types of glycosides is formed from glucose?
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In the biosynthesis of glycosides, what is the role of uridine triphosphate (UTP)?
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What is the primary method to purify crude glycosides after extraction?
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Which glycoside type is indicated by the presence of an SH group in its structure?
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What is a crucial step to inactivate hydrolyzing enzymes during glycoside extraction?
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Which of the following groups does not include a glycoside based on the whole aglycon classification?
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The removal of excess lead acetate in glycoside extraction is accomplished by using which gas?
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Study Notes
Glycosides Explained
- Glycosides are organic compounds, typically found in plants, consisting of a sugar portion (glycon) linked to a non-sugar portion (aglycon) through a glycosidic bond.
- There are four main types of glycosides based on their structure: C-glycosides, O-glycosides, S-glycosides, and N-glycosides.
- Glycosides can be broken down into their sugar and non-sugar components through enzymatic or acid hydrolysis.
- Both α and β forms of glycosides exist, but the β-form is more common in plants.
- The difference between α and β forms lies in the orientation of the hydroxyl group on the anomeric carbon (C-1) of the sugar.
- Glycosides are acetals where the hydroxyl group of the glycon condenses with the hydroxyl group of the aglycon.
- The sugar portion of the glycosides is crucial for solubility, impacting absorption and distribution in the body.
- The non-sugar portion (aglycon) is responsible for the pharmacological activity of the compound.
- Glycosides exhibit diverse solubility properties.
- Most glycosides are soluble in water or hydroalcoholic solutions due to the sugar moiety's contribution to water solubility.
- The aglycon part is soluble in non-polar solvents like benzene, ether, and chloroform.
- Glycosides exhibit varying stability.
- They can be hydrolyzed by heating with a dilute acid, breaking the glycosidic linkage.
- Glycosides are relatively stable towards alkalis.
- Specific enzymes found in plants can also hydrolyze glycosides, often located separately from the glycosides themselves.
- Each glycoside usually has a specific enzyme that hydrolyzes it.
- The same enzyme may be capable of hydrolyzing different glycosides but typically does not hydrolyze α and β stereo-isomers of the same glycoside. For example, Emulsin hydrolyzes most β-glycoside linkages, while maltase and invertase are α-glycosidases.
- Glycosides are solid, amorphous, non-volatile, and odorless.
- Most glycosides are bitter, except for saponin (glycyrrhizin) which is sweet.
- Glycosides are important in various aspects of plant life:
- Sugar reserves
- Waste products of plant metabolism
- Detoxification mechanisms
- Osmotic regulation
- Regulation of key substances involved in metabolism
- Defense against microbial invasion. Aglycones often exhibit antiseptic properties because of their bactericidal nature.
- Glycosides are valuable therapeutic agents, contributing to a wide range of drug classes:
- Cardiac glycosides like digitalis, strophanthus, and squill.
- Laxative drugs such as senna, aloe, rhubarb, cascara sagrada, and frangula, contain emodin and other anthraquinone glycosides.
- Sinigrin, a glycoside from black mustard, yields allyl isothiocyanate – a potent local irritant.
- Glycosides can be classified based on:
- The type of glycosidic linkage: α-glycosides or β-glycosides.
- The chemical group involved in the formation of the glycoside linkage: O-glycosides, C-glycosides, S-glycosides, and N-glycosides.
- The chemical nature of the aglycon, including cardioactive, anthraquinone, saponin, cyanophore, isothiocyanate, flavonol, alcohol, aldehyde, and phenol groups.
- The nature of the simple sugar component:
- Glucoside (glycone is glucose)
- Galactoside (glycone is galactose)
- Mannoside (glycone is mannose)
- Arabinoside (glycone is arabinose)
- The biosynthesis of glycosides is a complex process where the aglycone and sugar components are synthesized separately and then coupled.
- The coupling involves phosphorylation of a sugar to form a sugar-1-phosphate, which then reacts with uridine triphosphate (UTP), resulting in UDP-sugar and inorganic phosphate.
- This UDP-sugar reacts with the aglycone to form the glycoside and free UDP.
- The extraction of glycosides involves:
- Inactivation of specific hydrolyzing enzymes by boiling the plant material in water or alcohol.
- Defatting or purification of plant material, especially for seeds.
- Treatment with lead acetate to remove tannins and other impurities.
- Removal of excess lead acetate by passing hydrogen sulfide (H2S) gas through the solution.
- Filtering and concentrating the extract to obtain crude glycosides.
- Purification of the crude glycosides using chromatography or crystallization.
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Description
This quiz covers the fundamentals of glycosides, organic compounds mainly found in plants. Explore their structure, types, and the differences between α and β forms. Understand the significance of both the sugar and non-sugar components in pharmacological activity.
