Monomers, Polymers and Carbohydrates

Monomers and polymers

A polymer is a large molecule made up of many monomers.

Condensation and hydrolysis

• A condensation reaction joins two molecules together, and water is produced.
• A hydrolysis reaction is the breakage of glycosidic bonds.

Monosaccharides and disaccharides

• Glucose, fructose and galactose are monosaccharides.
• Carbohydrates are composed of carbon, hydrogen and oxygen.
• Two monosaccharides join by condensation, forming a glycosidic bond.

• Maltose and sucrose are both C₁₂H₂₂O₁₁, formed from two monomers with formula C₆H₁₂O₆, joined by a glycosidic bond.
• Sucrose contains fructose; maltose does not.
• Write glucose and fructose for sucrose. Never write β-glucose in the structure of sucrose.

α-glucose and β-glucose

• α-glucose and β-glucose are isomers: same chemical formula but different structural formula.
• They differ in the positions of the H and OH on carbon 1: in α-glucose the OH is below the ring, in β-glucose above it.
• Starch and glycogen are polymers of α-glucose; cellulose is a polymer of β-glucose. Never write α-glucose as the monomer of cellulose.

Joining and splitting carbohydrates

• Any two sugar rings join through an O between two carbons: this is a glycosidic bond, and H₂O is released.
• Formula of the product = the monosaccharide formulae added together, minus one H₂O for each bond formed.
• Splitting a glycosidic bond adds H₂O: an OH group is drawn on each carbon that was joined by the bond.
• To identify the bond in a larger carbohydrate, circle the O that links two rings.