Carbohydrates and Fischer Projections
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Questions and Answers

Which of the following is NOT a function of carbohydrates?

  • Carry genetic information (correct)
  • Form part of structural elements of cells & tissues
  • Serve as a stored form of chemical energy
  • Provide energy through oxidation

    • The simplest carbohydrate is glyceraldehyde.

    True (A)

    What is the name given to mirror-image isomers of molecules?

    Enantiomers

    A carbon atom with four different groups attached is called a ______ carbon.

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

    Glucose has 8 isomers.

    <p>False (B)</p> Signup and view all the answers

    What is the name of the two-dimensional representation of mirror-image isomers that is used to simplify their structures?

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

    Which of the following is the convention used to categorize sugars based on the position of the hydroxyl group farthest from the carbonyl group in their Fischer projection?

    <p>D and L prefixes (A)</p> Signup and view all the answers

    The D family of compounds means that the hydroxyl group farthest from the carbonyl group projects to the left in a Fischer projection.

    <p>False (B)</p> Signup and view all the answers

    Enantiomers can be differentiated based on their different optical activities.

    <p>True (A)</p> Signup and view all the answers

    Which of the following is NOT a key characteristic of stereoisomers in living organisms?

    <p>Enantiomers often co-exist in the same biological system in equal amounts (B)</p> Signup and view all the answers

    What is the term used for carbohydrates composed of two monosaccharide units linked together chemically?

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

    Match the following carbohydrate classification terms with their corresponding descriptions:

    <p>Monosaccharide = Consist of a single polyhydroxy aldehyde or ketone unit Disaccharide = Composed of two monosaccharide units linked together Oligosaccharide = Contain 3 to 10 monosaccharide units Polysaccharide = Consist of very long chains of linked monosaccharide units</p> Signup and view all the answers

    Flashcards

    Functions of Carbohydrates

    1. Provide energy 2) Supply carbon 3) Stored energy 4) Structural role

    Carbohydrate Definition

    Polyhydroxy aldehydes or ketones, or substances yielding such on hydrolysis.

    Glyceraldehydes

    Simplest carbohydrate, can exist in two isomeric forms (isomers).

    Enantiomers

    Mirror-image isomers with the same formula but different spatial arrangements.

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    Chiral Carbon

    A carbon atom attached to four different groups.

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    Stereoisomers

    Molecules with the same formula but different orientations of atoms.

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    Fischer Projections

    2D representations of molecules to indicate stereochemistry.

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    D and L Isomers

    Designations for stereoisomers based on hydroxyl orientation.

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    Optical Activity

    The ability of a compound to rotate polarized light.

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    Levorotatory

    Enantiomer that rotates polarized light to the left.

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    Dextrorotatory

    Enantiomer that rotates polarized light to the right.

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    Living Organisms and Chiral compounds

    Living organisms primarily consist of chiral substances.

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    Monosaccharides

    Simple carbohydrates made of a single sugar unit.

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    Disaccharides

    Carbohydrates composed of two monosaccharide units.

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    Oligosaccharides

    Carbohydrates made of 3 to 10 monosaccharide units.

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    Polysaccharides

    Complex carbohydrates with long chains of monosaccharide units.

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    Aldoses

    Monosaccharides with an aldehyde group.

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    Ketoses

    Monosaccharides with a ketone group.

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    Trioses

    Monosaccharides with 3 carbon atoms.

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    Tetroses

    Monosaccharides with 4 carbon atoms.

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    Pentoses

    Monosaccharides with 5 carbon atoms.

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    Hexoses

    Monosaccharides with 6 carbon atoms.

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    D-Ribulose

    A ketopentose, important in biological processes.

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    D-Glucose

    A common aldohexose, sweet and nutritious.

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    D-Galactose

    An aldohexose found in milk sugar.

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    D-Mannose

    An aldohexose important in human metabolism.

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    D-Arabinose

    A pentose involved in polysaccharide structure.

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    Natural Occurrence of D and L Isomers

    D and L forms often found in nature, but usually not together.

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    Stereochemical Role

    Orientation of atoms affects biological activity.

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    Study Notes

    Carbohydrates

    • Carbohydrates have four main functions: providing energy through oxidation, supplying carbon for cell components, serving as a stored form of energy, and forming structural elements in some cells and tissues.
    • Carbohydrates are polyhydroxy aldehydes or ketones, or substances that yield these compounds upon hydrolysis.
    • Glyceraldehyde, the simplest carbohydrate, exists in two isomeric forms (mirror images) called enantiomers.
    • A chiral carbon is a carbon atom bonded to four different groups.
    • The carbon atom in glyceraldehyde is chiral, leading to two enantiomers (D and L).
    • Enantiomers are nonsuperimposable mirror images.
    • Organic molecules, like carbohydrates, may have more than one chiral carbon.

    Fischer Projections

    • Fischer projections represent molecules in two dimensions to show mirror images.
    • L-Glyceraldehyde and D-Glyceraldehyde are enantiomers.
    • The D-isomer is when the -OH group is on the right of the chiral carbon.
    • The L-isomer is when the -OH group is on the left of the chiral carbon.
    • This system helps to determine the D and L configuration of sugars.
    • Isomers have the same chemical formula but different spatial arrangement of their atoms.

    Physical Properties and Optical Activity

    • D and L isomers generally have the same physical properties except for rotation of polarized light.
    • Enantiomers that rotate polarized light to the left are levorotatory (-).
    • Enantiomers that rotate polarized light to the right are dextrorotatory (+).
    • Optical activity is the property of rotating the plane of polarized light.
    • Optical activity is useful for differentiating between stereoisomers.
    • Stereoisomers are important in living organisms.

    Stereoisomers in Living Organisms

    • Living organisms often use only one stereoisomer (like L-amino acids).
    • D-glucose is a common carbohydrate.
    • Not all molecules with chiral carbons only contain one isomer.

    Classification of Carbohydrates

    • Classification is based on the number of molecules:
      • Monosaccharides: one molecule
      • Disaccharides: two molecules
      • Oligosaccharides: 3-10 molecules
      • Polysaccharides: many molecules (hundreds or thousands)
    • Monosaccharides are classified by the number of carbons: Trioses, Tetroses, Pentoses, Hexoses and etc.
    • Glucose is an aldohexose, a six-carbon sugar with an aldehyde group.
    • Ribulose is a ketopentose, a five-carbon sugar with a ketone group

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    Carbohydrates PDF

    Description

    This quiz explores the fundamental concepts of carbohydrates, their functions, and the structural representation of molecules using Fischer projections. Understand the significance of chiral carbons and the formation of enantiomers like glyceraldehyde. Test your knowledge on these essential topics in organic chemistry.

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