Biochemistry: Sugars and Isomerism
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Biochemistry: Sugars and Isomerism

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Questions and Answers

What type of isomers have the same molecular formula but differ in the grouping of their functional groups?

  • Functional group isomers (correct)
  • Positional isomers
  • Cis-trans isomers
  • Structural isomers

    • Which of the following best describes a racemic mixture?

  • A mixture containing equal concentrations of d- and l- isomers (correct)
  • A mixture with one optical isomer
  • A mixture of glyceraldehyde and dihydroxyacetone
  • A mixture of two structural isomers

    • What property is exhibited by compounds with an asymmetric carbon atom?

  • Thermal conductivity
  • Increased melting point
  • Chemical stability
  • Optical activity (correct)

    • Which isomer has substituent groups positioned differently on carbon atoms?

    <p>Positional isomers</p> Signup and view all the answers

    What is the term used for isomers that have the same structural formula but differ in spatial arrangement?

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

    What type of isomerism occurs when there is a distinction in orientation around double bonds?

    <p>Cis-trans isomerism</p> Signup and view all the answers

    Which of the following is true about dextrorotatory and levorotatory compounds?

    <p>They rotate plane polarized light in opposite directions</p> Signup and view all the answers

    What occurs when a recemic mixture is formed?

    <p>The optical activities cancel each other out</p> Signup and view all the answers

    What type of stereoisomers are the two aldotetroses described?

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

    In the context of aldohexoses, how do C-4 epimers differ?

    <p>They differ only in the position of the hydroxyl group on carbon 4.</p> Signup and view all the answers

    Which representation is primarily used for depicting straight chains of sugars?

    <p>Fisher projection</p> Signup and view all the answers

    In the Haworth projection, if a substituent is on the right in the Fisher projection, where will it be drawn?

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

    For D-sugars, where is the hydroxyl group at the anomeric position drawn in the Haworth projection?

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

    How are the configurations of D-sugars and L-sugars differentiated in their representation?

    <p>By the orientation of the highest numbered carbon</p> Signup and view all the answers

    Which of the following best describes the representation of aldohexoses?

    <p>Most are depicted as six-membered rings.</p> Signup and view all the answers

    What type of cyclic representation includes oxygen as one of its atoms?

    <p>Haworth projection</p> Signup and view all the answers

    What characterizes an enantiomeric pair?

    <p>They have the same molecular formula but differ in spatial arrangement.</p> Signup and view all the answers

    What is the effect of a dextrorotatory compound on polarized light?

    <p>It rotates light in a clockwise direction.</p> Signup and view all the answers

    If a compound has 4 asymmetric carbon atoms, how many different optical isomers can it have?

    <p>16</p> Signup and view all the answers

    Which of the following statements is true about aldotetroses?

    <p>D-erythrose and L-erythrose are enantiomers.</p> Signup and view all the answers

    Which of the following compounds is levorotatory?

    <p>D-arabinose</p> Signup and view all the answers

    What is the label for a compound that rotates polarized light counterclockwise?

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

    How many asymmetric carbon atoms does a 5-carbon aldose have?

    <p>3</p> Signup and view all the answers

    Which of the following compounds has a specific rotation of +66.5 degrees?

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

    What is the number of optical isomers for a ketose with 1 asymmetric carbon atom?

    <p>2</p> Signup and view all the answers

    Which factor determines the number of optical isomers a compound can have?

    <p>The number of asymmetric carbon atoms in the molecule.</p> Signup and view all the answers

    What is the primary form of D-glucose in aqueous solution?

    <p>Pyranose form</p> Signup and view all the answers

    What characterizes the pyranose ring structure?

    <p>It consists of a six-membered cyclic ether.</p> Signup and view all the answers

    What type of reaction results in the formation of a pyranose structure from D-glucose?

    <p>Intramolecular nucleophilic addition</p> Signup and view all the answers

    Which of the following statements about anomers is true?

    <p>They are an example of stereoisomers.</p> Signup and view all the answers

    What happens during mutarotation?

    <p>Conversion of one anomer to another.</p> Signup and view all the answers

    Which conformation is not typically associated with pyranose sugars?

    <p>Plane conformation</p> Signup and view all the answers

    How is the anomeric center defined?

    <p>As the former carbonyl carbon in cyclic form.</p> Signup and view all the answers

    Which statement accurately describes D-ribose?

    <p>It exists as a pentose sugar.</p> Signup and view all the answers

    In B-D-glucose, what type of substituents are present in the chair conformation?

    <p>Both axial and equatorial</p> Signup and view all the answers

    What is the equilibrium ratio of α-anomer to β-anomer of D-glucose?

    <p>36% α-anomer, 63% β-anomer</p> Signup and view all the answers

    Which of the following best describes a chair conformation?

    <p>Allows for minimal steric hindrance.</p> Signup and view all the answers

    What distinguishes an aldohexose from a ketohexose?

    <p>Presence of a carbonyl group on C1.</p> Signup and view all the answers

    Which sugar structure has a higher propensity for glycosidic bond formation?

    <p>α-anomer</p> Signup and view all the answers

    Which of the following is NOT typically a link found in polysaccharides?

    <p>γ(1→4)</p> Signup and view all the answers

    What impact does water have on the structure of glucose?

    <p>It promotes the formation of a six-membered ring.</p> Signup and view all the answers

    Study Notes

    Differences in Sugars

    • Variations in sugar structures lead to differences in physical properties, chemical reactions, and physiological effects.
    • Key physical properties influenced by structure include crystalline form, solubility, and rotatory power.
    • Chemical reactions can include oxidation, reduction, and condensation processes.
    • Physiological differences can affect nutritive value for humans and bacteria, sweetness perception, and absorption rates.

    Isomerism

    • Structural isomers have the same molecular formula but differ in structure.

      • Functional group isomers have different functional groups (e.g., glyceraldehyde vs. dihydroxyacetone).
      • Positional isomers have substituent groups on different carbon atoms.

    • Stereoisomers share the same structural formula but differ in spatial arrangement.

      • Cis-trans isomers have different configurations around double bonds (e.g., fumaric acid and maleic acid).
      • Optical isomers display optical activity due to asymmetric carbon atoms, rotating polarized light either to the right (dextrorotatory) or left (levorotatory).

    • Racemic mixtures contain equal concentrations of d- and l- isomers, showing no net optical activity due to canceling effects.

    Optical Isomers

    • A compound with 'n' asymmetric carbon atoms can produce 2^n optical isomers.
    • D-glucose, for example, has specific optical activity values:
      • D-glucose +52.7, D-fructose -92.4, and D-galactose +80.2, among others.

    Types of Isomers

    • Aldoses and ketoses are types of sugars with varying degrees of asymmetric carbon atoms, impacting the number of optical isomers possible.
    • D- and L-sugars differ in orientation of the highest numbered carbon, influencing their chemical behavior and interaction.

    Fisher Projection and Haworth Projection

    • Different structural representations exist for sugars: Fischer (straight chain) and Haworth (ring structure).
    • The Down-Right Rule dictates the drawing orientation of substituents in Haworth projections based on Fischer projections.

    Sugar Cyclization

    • D-glucose can form cyclic structures (pyranose and furanose) through intramolecular nucleophilic addition.
    • Pyranose form is six-membered, while furanose form is five-membered, influenced by the positioning of hydroxyl groups.

    Conformational Isomers

    • Pyranose rings exhibit chair and boat conformations.
    • Mutarotation is the process where anomeric forms (α and β) of sugars interconvert over time, establishing an equilibrium.

    Anomers and Anomeric Center

    • Anomers are diastereomers that differ at the anomeric carbon, which is derived from the carbonyl carbon during ring formation.
    • The terms D- and L- refer to configuration based on the highest numbered chiral center's orientation.

    Summary of Sugar Structures

    • Most aldohexoses tend to form six-membered rings, while smaller sugars may form five-membered rings.
    • Anomalous linkages exist in polysaccharides, affecting their structure and flexibility.

    Conclusion

    • Understanding sugar isomerism is crucial in biochemistry, influencing nutrition, metabolism, and cellular functions.
    • The diverse structural forms of sugars lead to significant biochemical implications.

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    Description

    Explore the fascinating differences in sugar structures and their impact on physical properties, chemical reactions, and physiological effects. Dive into isomerism, understanding both structural and stereoisomers, along with their significance in biochemistry.

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