Carbohydrate Chemistry: Monosaccharides and Polysaccharides
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Questions and Answers

What happens to a beam of plane-polarised light when it passes through a solution exhibiting optical activity?

  • It is reflected back
  • It is rotated to the right or left depending on the type of compound (correct)
  • It remains unchanged
  • It is absorbed by the solution
  • What is the term for a mixture of equal amounts of dextrorotatory and laevorotatory isomers?

  • Racemic (correct)
  • Optically active
  • Anomeric
  • Isomeric
  • What is the process of separating optically active isomers from a racemic mixture?

  • Cyclization
  • Resolution (correct)
  • Racemization
  • Optical rotation
  • What is the term for the carbon atom that becomes asymmetric after cyclization in a monosaccharide?

    <p>Anomeric carbon</p> Signup and view all the answers

    What is the term for a pair of cyclic compounds that are not mirror images of each other?

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

    What is the general formula of monosaccharides?

    <p>CnH2nOn</p> Signup and view all the answers

    What is the classification of carbohydrates based on the number of carbon atoms?

    <p>Trioses, Tetroses, Pentoses, Hexoses</p> Signup and view all the answers

    What is the type of carbohydrate that cannot be hydrolyzed further into simpler forms?

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

    What is the general formula of disaccharides?

    <p>Cn(H2O)n-1</p> Signup and view all the answers

    What type of carbohydrates yields two molecules of the same or different molecules of monosaccharide on hydrolysis?

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

    Study Notes

    Carbohydrates

    • Consist of covalently linked monosaccharide units, often associated with proteins (glycoproteins) and lipids (glycolipids) with structural and regulatory functions.

    Polysaccharides (Glycans)

    • Composed of more than 10 molecules of monosaccharides on hydrolysis, with a general formula of (C6H10O5)n.
    • Have molecular masses ranging into millions of daltons and serve indispensable structural functions in all types of organisms.
    • Most conspicuous in plants, where cellulose comprises up to 80% of dry matter.

    Classification of Polysaccharides

    • Divided into two groups: homopolysaccharides (homoglycans) and heteropolysaccharides (heteroglycans).
    • Homopolysaccharides: polymers of same monosaccharide units, e.g. starch, glycogen, inulin, cellulose, dextrins, and dextrans.
    • Heteropolysaccharides: polymers of different monosaccharide units or their derivatives, e.g. mucopolysaccharides (glycosaminoglycans).

    General Properties of Carbohydrates

    • Isomerism: due to asymmetric carbon atoms, compounds can exhibit stereoisomerism, resulting in isomers with identical composition but differing only in spatial configuration.
    • D-Series and L-Series: the orientation of H and OH groups around the carbon atom determines whether a sugar belongs to D-series (OH group on the right) or L-series (OH group on the left).
    • Most monosaccharides in mammals are D-sugars, and enzymes responsible for their metabolism are specific for this configuration.

    Chemistry of Carbohydrates

    • Carbohydrates or saccharides (Greek: sakcharon, sugar) have a chemical composition of “carbon hydrate” (CH2O)n, where n ≥ 3.
    • Essential and most abundant class of biological molecules, with the basic units being monosaccharides.
    • Aldehyde or ketone derivatives of higher polyhydric alcohols or compounds that yield these derivatives on hydrolysis.

    Classification of Carbohydrates

    • Divided into four major groups: monosaccharides, disaccharides, oligosaccharides, and polysaccharides.

    Monosaccharides

    • Also known as simple sugars, cannot be hydrolyzed further into simpler forms.
    • Aldehyde or ketone derivatives of straight-chain polyhydroxy alcohols containing at least three carbon atoms, with a general formula of CnH2nOn.

    Sub-classification of Monosaccharides

    • Based on the number of carbon atoms: trioses, tetroses, pentoses, hexoses, etc.
    • Based on aldehyde (– CHO) or ketone (– CO) groups: aldoses and ketoses.

    Disaccharides

    • Hydrolysis produces two molecules of the same or different monosaccharides, with a general formula of Cn(H2O)n-1.
    • Examples include maltose, lactose, sucrose, and lactulose.

    Oligosaccharides

    • Composed of 3 to 10 monosaccharide units on hydrolysis.

    Optical Activity of Carbohydrates

    • Presence of asymmetric carbon atoms confers optical activity on compounds.
    • Dextrorotatory (D or + sign) and laevorotatory (L or – sign) compounds rotate plane-polarized light to the right or left, respectively.
    • Racemic mixtures: equal amounts of dextrorotatory and laevorotatory isomers, resulting in no optical activity.
    • Resolution: separation of optically active isomers from a racemic mixture.

    Cyclic Structures of Carbohydrates

    • Formation of cyclic structures from open-chain forms of monosaccharides, resulting in anomers.
    • Anomeric carbon atom: the carbon atom that becomes asymmetric after cyclization, leading to the formation of different anomers.

    Biomedical Importance of Carbohydrates

    • Energy source
    • Structural functions
    • Carbon skeleton

    Optical Activity and Isomerism

    • Presence of asymmetric carbon atoms confers optical activity on a compound.
    • When a beam of plane-polarized light is passed through a solution exhibiting optical activity, it will be rotated to the right (dextrorotatory, D or + sign) or left (laevorotatory, I or – sign).
    • A racemic mixture contains equal amounts of dextrorotatory and laevorotatory isomers, resulting in no optical activity.
    • Resolution is the separation of optically active isomers from a racemic mixture.

    Cyclic Structures and Anomers

    • The reaction between an aldehyde group and an alcoholic-OH group on the same molecule forms a cyclic structure.
    • This reaction can form two different forms of glucose: α-D-Glucose (OH group extends to the right) and β-D-Glucose (OH group extends to the left).
    • Carbon-1 becomes asymmetric after cyclization and is called an anomeric carbon atom.
    • Compounds related in this way are called anomers.

    Biomedical Importance and Energy Structure

    • Carbohydrates have both structural and regulatory functions in biological systems.
    • They are associated with proteins (glycoproteins) and lipids (glycolipids).
    • Polysaccharides consist of many covalently linked monosaccharide units and have molecular masses ranging from millions of daltons.

    Polysaccharides

    • Polysaccharides are composed of more than 10 molecules of monosaccharides on hydrolysis.
    • General formula: (C6H10O5)n.
    • They have indispensable structural functions in all types of organisms.
    • Polysaccharides are further divided into two groups: homopolysaccharides (homoglycans) and heteropolysaccharides (heteroglycans).

    Homopolysaccharides and Heteropolysaccharides

    • Homopolysaccharides are polymers of the same monosaccharide units, e.g., starch, glycogen, inulin, cellulose, dextrins, and dextrans.
    • Heteropolysaccharides are polymers of different monosaccharide units or their derivatives, e.g., mucopolysaccharides (glycosaminoglycans).

    General Properties of Carbohydrates

    • Isomerism: the presence of asymmetric carbon atoms in a compound gives rise to the formation of isomers.
    • Stereoisomerism: compounds that are identical in composition and differ only in spatial configuration.
    • D-Series and L-Series: the orientation of the H and OH groups around the carbon atom determines the series.

    Chemistry and Structure of Carbohydrates

    • Carbohydrates are also known as saccharides (Greek: sakcharon, sugar).
    • They have the general formula (CH2O)n, where n ≥ 3.
    • The basic units of carbohydrates are monosaccharides.
    • Carbohydrates are essential and the most abundant class of biological molecules.

    Classification of Carbohydrates

    • Carbohydrates are divided into four major groups: monosaccharides, disaccharides, oligosaccharides, and polysaccharides.
    • Monosaccharides are also known as simple sugars and cannot be hydrolyzed further into simpler forms.
    • They have the general formula CnH2nOn.

    Sub-classification of Monosaccharides

    • Based on the number of carbon atoms: trioses, tetroses, pentoses, hexoses, etc.
    • Based on the aldehyde or ketone groups: aldoses and ketoses.

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    Description

    This quiz covers the structure and function of monosaccharides and polysaccharides, including their relationship with proteins and lipids. Test your knowledge of carbohydrate chemistry!

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