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 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

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

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

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

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)

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

Hemiacetalization Concept Key to Carbohydrate Ring Structures

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

Polysaccharides –refer to polymers composed of a large number of monosaccharides linked by glycosidic linkages

Cellulose  -D-anhydroglucopyranose units linked by (1,4)-glycosidic bonds

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 LinearBranched 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

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

Homopolysaccharides Homopolysaccharides can be further divided by the type(s) of glycosidic linkages Homolinkages Homolinkages - either an α or a β configuration 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 Heterolinkages - a mixture of a- and b- configurations and/or mixture of positions usually have a definite pattern for the arrangement of the linkages

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

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

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

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 Plant Polysaccharides

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  -(1-4) to each other between 250-5,000 glucose residues

The Components of Starch Amylose

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

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

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

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