Structural Polysaccharides: Chitin vs Cellulose

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10 Questions

What is a chiral carbon?

Attached to four different atoms or groups

Which term describes an object that cannot be superimposed on its mirror image?

Chiral

Which representation of biological molecules provides a 3-D view?

Ball and stick

What is the purpose of using glyceraldehyde as a reference compound?

To designate D and L configurations

How are compounds designated as D or L sugars?

Based on the location of the hydroxy group on the penultimate carbon

For aldo-sugars, which carbon receives the lowest possible number in priority?

Carbonyl carbon

What determines whether a monosaccharide is designated as a D sugar?

Its configuration compared to D-glyceraldehyde

In the context of molecules, what does 'chiral' specifically refer to?

'Chiral' means non-superimposable on its mirror image

'Priority increases as atomic number increases' is associated with which rule?

"Priority Rule #1"

'D' and 'L' designations are given based on the configuration compared to which compound?

'D-Glyceraldehyde'

Study Notes

Starch and Cellulose

  • Starch is composed of 1-4 linkages of α glucose monomers.
  • Cellulose is composed of 1-4 linkages of β glucose monomers.

Chitin

  • Chitin is the major component of arthropod exoskeletons and fungal cell walls.
  • It is a linear homopolysaccharide composed of N-acetylglucosamine linked by β(1→4) glycosidic bonds.
  • Chitin exists in three arrangements: α-Chitin (all parallel), β-Chitin (antiparallel), and γ-Chitin (pairs of parallel sheets separated by single antiparallel sheets).
  • Chitin is used to make strong and flexible surgical threads that decompose after healing.

Heteropolysaccharides

  • Heteropolysaccharides are often made up of repeating disaccharide units.
  • The carbohydrate component of peptidoglycan is made up of a repeating disaccharide unit consisting of N-acetylglucosamine (NAG/GlcNAc) and N-acetylmuramic acid (NAM/Mur2Ac).

Cellulose Structure

  • Cellulose is rigid and water-insoluble due to its β(1→4) glycosidic linkage.
  • The β(1→4) glycosidic linkage allows cellulose to form long straight chains.
  • Cellulose chains associate with each other via extensive hydrogen bonding, forming cellulose microfibrils.
  • Cellulose is predominantly of plant origin, but also occurs in the outer mantles of tunicates/sea squirts.

Cellulose Function

  • The role of cellulose is to provide structural support and rigidity to plant cell walls.
  • The structure of cellulose is suited to its function due to its rigid and water-insoluble properties.

Carbohydrate Representations

  • Carbohydrates can be represented using ball and stick, perspective, and Fischer projection formulas.
  • Glyceraldehyde is a reference compound used to name other compounds based on their relative configuration.

Chirality

  • Chiral carbons are attached to four different atoms or groups.
  • An object that cannot be superimposed on its mirror image is also said to be chiral.
  • D and L designations are given based on the relative configuration of a compound compared to glyceraldehyde.

This quiz covers the structural differences between chitin and cellulose, two important polysaccharides. Learn about the composition, linkage of monomers, and chemical distinctions between chitin and cellulose.

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