AS Biology F212: Carbohydrates

Functions of Carbohydrates:

• Energy source (for respiration)
• Energy store (starch and glycogen)
• Structure (cellulose)

Elements of: C, H, and O.

Simple sugars

• Simple sugars: monosaccharides
• 3 carbon monosaccharides: triose
• 5 carbon monosaccharides: pentose
• 6 carbon monosaccharides: hexose
• Most common monosaccharides are hexoses: glucose, fructose, galactose
• Glucose C6H12O6

Molecular structure of alpha-glucose and beta-glucose

• Glucose is the building block for larger carbohydrates
• This is achieved by joining glucose molecules together using glycosidic bonds
• the bonds form between the C1 on one molecule and C4 on the other

• Two monosaccharides joined by a glycosidic bond is called a disaccharide. 
• eg. glucose + glucose = maltose
• glucose + galactose = lactose (milk)
• glucose + fructose = sucrose

Reducing sugars

• Benedict's reagent: used to test reducing sugars
• Postive test: blue to orange
• Sucrose
• To make sucrose give a positive test with benedict's reagent:
• Sucrose + HCl -biol-benedict's reagent-> positive test (orange)

Polysaccharides

• Three or more monosaccharides make a polysaccharide
• e,g, amylose (starch)
• Glycogen: 
• In animal cells glucose is stored as glycogen
• glycogen is a polymer or alpha-glucose
• basic structure is like amylose but has extra branches
• Starch
• Starch is stored food in plant
• It is made of a alpha-glucose units
• It consists of: Amylose: long unbranched chains with alpha 1,4 glycosidic bonds
• and Amylopection: branched chains with alpha 1,4 and 1,6 glycosidic bonds
• It can be broken down to glucose which can be respired to release energy
• Energy storage
• Compact: more energy in less space than glucose
• Insoluble: doesnt dissolve and change water potential of cell
• Cellulose:
• polymer of beta glucose
• 1, 4 glycosidic and hydrogen bonds
• about 60-70 cellulose molecules become crosslinked by H bonds to form bundles called microfibrils.
• Structural
• Strong: supports the plant, prevents cells from bursting
• Fully permeable: allows water and solutes to reach the cell membrane