Carbohydrates

Carbohydrates (Sugars)

• Can be simple sugars (monosaccharides), disaccharides, or polysaccharides.
• A disaccharide is two monosaccharides joined together;
• A polysaccharide is many monosaccharides joined together.

Structure of Monosaccharides

1. Carbon chain or ring
2. Functional groups off the side:
3. Hydroxyl (OH)
4. Carbonyl (C = O)
5. At end of chain: aldehyde
6. In the middle of chain: ketone Example: glucose (C6H12O6)

• Sometimes monosaccharides have the same chemical formula, but their functional groups are located in different places. We call all of these monosaccharides with the same formula isomers.
• Structural isomers have functional groups located on different carbons. Example: glucose vs fructose.
• Stereoisomers have functional groups are on the same carbon but different arrangements. Example: glucose vs galactose.

• Monosaccharides can be found as straight lines (linear) or rings.

Disaccharides

• Monosaccharides are joined together by a dehydration or condensation reaction to form a glycosidic linkage.
• Common disaccharides include lactose (milk), and sucrose (table sugar).

Polysaccharides

• Oligosaccharides: multiple monosaccharides attached together (3-10).
• Polysaccharides: more than 10 monosaccharides attached together.
• Examples of polysaccharides include: starch, glycogen, cellulose and chitin.
• Polysaccharides can have structural roles (cellulose and chitin), or they may be used for energy storage (starch and glycogen).

Storage Polysaccharides

• Starch – main sugar storage of plants and some algae (helical shape).
• Amylose: linear glucose polymer with glycosidic linkages
• Amylopectin: amylose with additional branches every 24-30 carbons
• Glycogen – main sugar storage of animals.
• Similar structure to amylopectin (branched).

Structural Polysaccharides

• Cellulose – main component of plant cell walls.
• Most abundant polysaccharide in nature.
• Glucose molecules linked together like in starch, but it uses a different isomer of glucose.
• Cellulase is the enzyme needed to break down cellulose, which very few organisms have; confers strong layer of protection to plant cells.

• Chitin – found in cell walls of fungi and in some animal exoskeletons.
• Doesn't use glucose, but instead uses the monomer acetylglucosamine.