Carbohydrates
Three categories of carbohydrates:
1. Simple sugars (monosaccharide)
2. Double sugars (disaccharides)
3. Macromolecules (polysaccharides)
Monosaccharide
Have the molecular formula CH2O.
Ratio of C:H:O of 1:2:1
Most common monosaccharide is glucose and has the chemical formula C6H12O6
In an aqueous solution, monosaccharides form rings
Disaccharide
A disaccharide is 2 monosaccharides joined by the glycosidic linkage, which is a covalent bond
formed by dehydration synthesis between to monosaccharides.
Most common disaccharides:
glucose + glucose  maltose
Glucose + fructose  sucrose
Glucose + Galactose  lactose
Glycosidic Linkages
Polysaccharides
Polymers of sugar – chains of sugar
Uses/functions
Storage of energy: Starch and glycogen
Building materials (structural components): Cellulose and Chitin
Polysaccharides for storage
Starch
Glycogen
Found only in plants.
Found only in animals
linkages are 1,4 and 1,6
various linkages
Helical in shape
Helical in shape
Some branching
Many branches
More on Starch and Glycogen
Starch will provide long-term storage of sugars. It is stored in plastids in plant cells. Hydrolysis will
release individual sugars as needed by the plant. We release sugars from starch with an enzyme in
our saliva called amylase.
Glycogen is stored in the liver and muscle cells and is only temporary. It is either used for energy or
transferred to fat cells within 24 hours.
 glucose and  glucose
glucose and glucose are 2 isomers of glucose.
Storage polysaccharides are made of glucose. Structural polysaccharides are made of -glucose.
Structural polysaccharides
Cellulose and chitin (pronounce “kite-in”) are both polysaccharides that are used in structure.
Cellulose is a strong fiber that is used by plants as part of their cell walls.
Chitin is used by fungi in their cell walls and in arthropods as their exoskeletons.
Made of glucose in straight chains (not helical and never branched)
The hydroxyl groups free to hydrogen bond
Parallel lines of cellulose molecules are held together into units called microfibrils
Who can digest cellulose?
The enzymes that hydrolyze starch cannot hydrolyze cellulose.
Many animals cannot digest cellulose, however, cows, horses, etc. have bacteria in their gut that can
hydrolyze cellulose.
Who can digest cellulose?
Termites have microbes living in their gut that can hydrolyze cellulose.
Chitin
Chitin is cellulose with a nitrogen-containing appendage.
Leathery in texture in fungus (like a mushroom).
Encrusted with calcium carbonate chitin becomes hard and makes up the outer shell of arthropods
(insects, lobsters, shrimp).