Annie Stetz & Peter Collins 5.2 Carbohydrates Annie Stetz & Peter Collins

Carbohydrate serve as fuel and building material: Carbohydrates: includes both sugars and polymers of sugars Simplest are monosaccharides (aka simple sugars) Disaccharides: double sugars 2 monosaccharides joined by a covalent bond Carbohydrates also include macromolecules Polysaccharides Polymers composed manly of sugar building blocks

Sugar Monosaccharides usually have molecular formulas that are some multiple of CH2O Glucose is the most common and is a keystone in the chemistry of life Diversity of simple sugars can be seen in the spatial arrangements of their parts around asymmetric carbon Monosaccharides are major nutrients for cells The carbon skeletons of single sugars serve as raw materials for the synthesis of other small organic molecules Disaccharides consist of 2 monosaccharides joined by a glyosidic linkage ( a covalent bond between 2 monosaccharides by a dehydration reaction) The most prevalent disaccharide is sucrose

Polysaccharides Polysaccharides are macromolecules Some serve as storage material others serve as building material for structures that protect cells or whole organisms

Storage Polysaccharides Both plants and animals store sugars in the form of storage polysaccharides Plants store starch, a polymer of glucose monomers. Because glucose is a major cellular fuel, starch represents stored energy Most animals, includes humans, have enzymes that hydrate plant starch Making glucose available to cells Most glucose monomers are joined together by 1-4 carbon linkages Animals store a polysaccharide called glycogen a polymer of glucose that is like a amylopectin but more extensively breached.

Structural Polysaccharides A polysacciraide called cellulose is a major component in the walls that enclose plant cell. Cellulose is a polymer of glucose, but the glycosidic linkages in these two polymers differ All glucose monomer are in an alpha configuration The differing glycosidic linkages in starch give it a three dimensional shapes Starch: helical Cellulose: straight In plant cell walls parallel cellulose molecules are grouped into microfibrils. Strong building materials for plants and an important substance for humans even though humans can not digest it Some prokaryotes, cows, and termites can digest cellulose

Structural Polysaccharides Chitin is another important structural polysaccharide The carbohydrate used by arthropods to build there exoskeletons Also found in many fungi Uses chitin to build their cell walls Similar to cellulose Except chitin has a nitrogen-containing appendages