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Building Blocks of Life

Building Blocks of Life. Most Important Chemical Consideration of Sugars. Consider the anomeric carbon! The aldehyde on the one position can be nucleophilically attacked by any of the hydroxyls!. Hemiacetalization Concept Key to Carbohydrate Ring Structures. Nomenclature of Carbohydrates .

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Building Blocks of Life

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  1. Building Blocks of Life

  2. Most Important Chemical Consideration of Sugars Consider the anomeric carbon! The aldehyde on the one position can be nucleophilically attacked by any of the hydroxyls!

  3. Hemiacetalization Concept Key to Carbohydrate Ring Structures

  4. Nomenclature of Carbohydrates • D, L Defines the configuration at C5 D has the OH at Right in Fischer projection L has the OH at Left in Fischer projection • Gluco defines the configuration of the OH at C2, C4, C5. These OH’s are on same side while the C3-OH is opposite to others • α,β defines the configuration of the OH at C1, the anomeric carbon • Pyran indicates 6 member ring size • Furan indicates 5 member ring size Examples follow

  5. In Glucuronic acid C2, C4, C5 OH’s are on same side

  6. Alditols • In Mannitol C2, C4, C5 OH’s are not at same side in Fisher Projection

  7. 25 25 [a] [a] D D For aged solutions = +52.7o Conformations Anomers Rotations of Fresh Solutions +19o +112o Reason: Mutarotation is the best evidence for the cyclic hemiacetal structure of D-(+)-glucose

  8. Monosaccharides,Hemiacetal Formation II C5 OH attacks aldehyde giving a pyranose ring (6 member structure) C4 OH attacks aldehyde giving a furanose ring (5 member structure)

  9. Ring closure between C1 and C4 -OH Ring closure between C1 and C5 -OH

  10. Hemiacetalization Concept Key to Carbohydrate Ring Structures

  11. Oligosaccharides • consist of several monosaccharide residues joined together with glycosidic linkages • di, tri, tetrasaccharides (depending on the number of monosaccharides) • up to 10 - 20 monosaccharides (depending on analytical techniques i.e GC vs LC/MS)

  12. Polysaccharides • refer to polymers composed of a large number of monosaccharides linked by glycosidic linkages

  13. Cellulose b-D-anhydroglucopyranose units linked by (1,4)-glycosidic bonds

  14. Polysaccharides Polysaccharides are polymers composed of many monosaccharide units linked by glycosidic bonds The glycosidic bond can can have either the α or a β-configuration and be joined to any of the hydroxyl groups at C-2, C-3, C-4 or C-6 The chain can either be Linear or Branched • branches can be single monosaccharide units, chains of two or more units, or chains of a variable number of units

  15. Polysaccharides Polysaccharides can be divided into two classes • Homopolysaccharides • consist of only one kind of monosaccharide ex cellulose • Heteropolysaccharides • consist of two or more kinds of monosaccharides ex galactoglucomannans

  16. Homopolysaccharides Homopolysaccharides can be further divided by the type(s) of glycosidic linkages Homolinkages - either an α or a βconfiguration to a single position (exclusive of any branch linkages) • that is a single kind of monosaccharide linked by one type of bond α-14, β-14, and so on Heterolinkages - a mixture of a- and b-configurations and/or mixture of positions • usually have a definite pattern for the arrangement of the linkages

  17. Heteropolysaccharides Heteropolysaccharides can have the same kind of linkage diversity as with homopolysaccharides, but now associated with one or more of the different kinds of monosaccharide units • infinite degree of diversity of structure

  18. Polysaccharides Polysaccharides can not only have different sequences of monosaccharide units, but also different sequences of glycosidic linkages and different kinds of branching • a very high degree of diversity for polysaccharides and their structure-function relationships

  19. Plant Polysaccharides The conformation of individual monosaccharide residues in a polysaccharide is relatively fixed, however, joined by glycosidic linkages, they can rotate to give different chain conformations. 1,4 glycosidic linkage 1,6 glycosidic linkage

  20. Plant Polysaccharides The different kinds of primary structures that result in secondary and tertiary structures give different kinds of properties • water solubility, aggregation and crystallization, viscosity, gelation, etc. Polysaccharides have a variety of functions • Storage of chemical energy in photosynthesis • Inducing Structural Integrity in plant cell walls

  21. Starch Starch is composed completely of D-glucose • found in the leaves, stems, roots, seeds etc in higher plants • stores the chemical energy produced by photosynthesis Most starches are composed of two types of polysaccharides - amylose and amylopectin • amylose - a mixture of linear polysaccharides of D-glucose units linked a-(1-4) to each other • between 250-5,000 glucose residues

  22. The Components of Starch Amylose

  23. Amylopectin • Amylopectin - a mixture of branched polysaccharides of D-glucose units linked a-(1-4), with ~ 5% a-(1-6) branch linkages • between 10,000-100,000 glucose residues

  24. Starch Polymer Components Amylose Amylopectin (1 residue in every 20 is 16 linked to branch off)

  25. The Components of Starch Amylopectin Amylose Starch tertiary structure (Helix)

  26. Cellulose 45 ± 2% Cellulose 42±2% Hemicelluloses 30 ± 5% Hemicelluloses 27 ± 2% Lignin 20 ± 4% Lignin 28 ± 3% Extractives 3 ± 2% Extractives 5 ± 3% Softwood Hardwood Composition of Softwoods and Hardwoods

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