Chirality in Carbohydrates
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Questions and Answers

What type of ring is formed by aldohexoses in Haworth projections?

  • Cyclic hemiacetal
  • Six-atom ring (correct)
  • Five-membered ring
  • Straight-chain structure

    • Which type of monosaccharide is associated with forming furanose rings?

  • Sugars with six carbons only
  • Aldopentoses and Ketohexoses (correct)
  • Aldohexoses
  • Hexoses

    • What is the common form of D-ribose in the biological context according to Haworth projections?

  • Furanose (correct)
  • Pyranose
  • Hexose
  • Straight-chain

    • How does D-Fructose exist in terms of structure in Haworth projections?

    <p>It forms a five-membered cyclic hemiacetal</p> Signup and view all the answers

    What is the characteristic view of a Haworth projection?

    <p>Edge on view of the hemiacetal ring</p> Signup and view all the answers

    Which statement accurately describes pyranose?

    <p>It can be formed by aldohexoses.</p> Signup and view all the answers

    What component of a Haworth projection is located at the upper right in a six-membered ring?

    <p>Oxygen ring atom</p> Signup and view all the answers

    What distinguishes the Dextro and Levo designation in Haworth projections?

    <p>Ring orientation and configuration</p> Signup and view all the answers

    How many chiral carbons are present in an aldohexose?

    <p>4</p> Signup and view all the answers

    Which of the following represents the number of chiral carbons in a ketopentose?

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

    In the Fischer projection, which lines represent bonds projecting forward from the stereocenter?

    <p>Horizontal lines</p> Signup and view all the answers

    What is the characteristic of a D-monosaccharide in terms of its penultimate carbon?

    <p>The -OH is on the right</p> Signup and view all the answers

    Which of the following carbohydrates has no chiral carbons?

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

    Which type of sugar has the highest number of chiral carbons among aldoses?

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

    In a Fischer projection of an L-monosaccharide, where is the -OH located on the penultimate carbon?

    <p>On the left</p> Signup and view all the answers

    How many chiral carbons are found in an aldotetrose?

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

    In the D form of glucose, where is the CH2OH group positioned?

    <p>Above the ring</p> Signup and view all the answers

    Which statement is true concerning the L form of glucose?

    <p>The CH2OH group is positioned below the ring.</p> Signup and view all the answers

    What shape does the six-membered ring of pyranoses adopt for better representation?

    <p>Strain-free chair conformation</p> Signup and view all the answers

    In the chair conformation of b-D-glucopyranose, what is the orientation of groups on carbons 1-5?

    <p>Up, down, up, down, up and all are equatorial</p> Signup and view all the answers

    How can Haworth projections and chair conformations be related?

    <p>They both have well-defined 'up' and 'down' positions.</p> Signup and view all the answers

    Which of the following accurately describes a characteristic of the chair conformation?

    <p>It minimizes steric strain in the ring.</p> Signup and view all the answers

    What feature distinguishes the D and L forms of sugars in terms of orientation?

    <p>The orientation of the OH group on the last asymmetric carbon</p> Signup and view all the answers

    What is typically NOT a characteristic of the L form of glucose?

    <p>The CH2OH group is above the ring.</p> Signup and view all the answers

    Which group replaces the -OH group in amino sugars?

    <p>-NH2 group</p> Signup and view all the answers

    What is another name for glucose?

    <p>Grape sugar</p> Signup and view all the answers

    Which monosaccharide is used to differentiate between blood types?

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

    Which of the following statements about glucose is true?

    <p>Glucose is the most abundant monosaccharide in nature.</p> Signup and view all the answers

    Which statement correctly describes galactose?

    <p>It is commonly known as milk sugar.</p> Signup and view all the answers

    Which of the following is NOT a common amino sugar?

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

    What type of sugar is primarily found in the brain?

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

    Which of these characteristics applies to glucose?

    <p>It is essential for human nutrition.</p> Signup and view all the answers

    What type of glycosidic bond links the two monosaccharides in maltose?

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

    Which disaccharide is composed of a β-D-galactose unit and a D-glucose unit?

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

    Which of the following statements is true about sucrose?

    <p>It is commonly known as table sugar.</p> Signup and view all the answers

    What is the structural composition of cellobiose?

    <p>Two D-glucose units with one in β configuration</p> Signup and view all the answers

    Which of the following is a characteristic of lactose?

    <p>Contains a β(1→4) glycosidic linkage</p> Signup and view all the answers

    How many monosaccharide units are found in oligosaccharides?

    <p>3–10 units</p> Signup and view all the answers

    What is the primary reason why cellobiose cannot be digested by humans?

    <p>It contains a β(1→4) glycosidic bond.</p> Signup and view all the answers

    Which food sources commonly contain oligosaccharides?

    <p>Onions and cabbage</p> Signup and view all the answers

    Study Notes

    Chirality in Carbohydrates

    • Aldoses and Chiral Carbons:

      • Aldotriose: 1 chiral carbon
      • Aldotetroses: 2 chiral carbons
      • Aldopentoses: 3 chiral carbons
      • Aldohexoses: 4 chiral carbons

    • Keto sugars and Chiral Carbons:

      • Ketotriose: no chiral carbons
      • Ketotetroses: 1 chiral carbon
      • Ketopentoses: 2 chiral carbons
      • Ketohexoses: 3 chiral carbons

    Fischer Projection

    • A method for representing tetrahedral stereocenters in two dimensions.
      • Horizontal lines indicate bonds projecting forward.
      • Vertical lines signify bonds projecting backward.
      • Only the stereocenter is in the plane.

    L- and D-Monosaccharides

    • Assignments of D- and L- to enantiomers of glyceraldehyde established by Emil Fischer in 1891.
      • D-monosaccharide: -OH on the penultimate carbon is on the right in Fischer projection.
      • L-monosaccharide: -OH on the penultimate carbon is on the left in Fischer projection.

    Haworth Projections

    • Represent cyclic forms of monosaccharides.

      • Pyranose: Six-membered ring, formed by aldohexoses.
      • Furanose: Five-membered ring, formed by aldopentoses and ketohexoses.

    • Aldopentoses typically form cyclic hemiacetals, predominantly as furanoses in nature.

    • D-Fructose also forms a five-membered cyclic hemiacetal.

    Dextro and Levo Designation

    • In Haworth projections, the orientations of groups determine D or L forms.
      • D form: CH2OH is above the ring.
      • L form: CH2OH is below the ring (less common in biochemistry).

    Chair Conformation

    • Pyranoses can be represented accurately in a strain-free chair conformation.
    • In β-D-glucopyranose:
      • Carbons 1-5 group orientations are up, down, up, down, and up, all equatorial.

    Converting Between Haworth and Chair

    • The positions (up and down) in Haworth projections translate to chair conformations.

    Carbohydrate Derivatives

    • Amino sugars: Contain an -NH2 group replacing an -OH group.
      • Three common amino sugars in nature.

    Biologically Relevant Carbohydrates

    • Monosaccharides:

      • Glucose: Most abundant; also known as grape, blood sugar, or dextrose; six-membered cyclic form essential for nutrition.
      • Galactose: Known as "brain sugar" and "milk sugar"; differentiated in blood types; six-membered cyclic form.

    • Disaccharides: Composed of two monosaccharides linked by glycosidic bonds.

      • Maltose: Composed of 2 D-glucose units, linked via α(1→4) glycosidic linkage; digestible by humans.
      • Lactose: Composed of β-D-galactose and D-glucose linked by β(1→4) glycosidic linkage; hydrolyzed by lactase.
      • Sucrose: Most abundant disaccharide, also known as table sugar, found in plants.
      • Cellobiose: Comprising two D-glucose units linked via β(1→4) glycosidic linkage; indigestible for humans.

    • Oligosaccharides: Contain 3-10 monosaccharide units, bonded via glycosidic linkages; commonly found in foods like onions and whole wheat.

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    Carbohydrates Structure & Functions Lecture Notes PDF

    Description

    Explore the concepts of chirality and the number of chiral carbons in aldoses and ketoses. This quiz covers various types of sugars including aldotrioses, aldoses, and ketoses. Test your knowledge on the structural aspects of these carbohydrates.

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