Monomers, Polymers and Carbohydrates

Monomers and polymers

• A monomer is a smaller, repeating unit from which larger molecules are made. Never write that monomers are atoms, elements or building blocks.
• A polymer contains many monomers joined together.
• A disaccharide is not a polymer. Never give triglycerides as polymers.

Condensation and hydrolysis

• A condensation reaction joins monomers together, forms a chemical bond and releases water.
• A hydrolysis reaction breaks a chemical bond between monomers and uses water.

Monosaccharides and disaccharides

• Glucose, galactose and fructose are monosaccharides.
• Carbohydrates contain carbon, hydrogen and oxygen.
• Two monosaccharides are joined by a condensation reaction, forming a glycosidic bond. Never write water added to form a disaccharide, and never name any other reaction or bond for forming a disaccharide.
• In maltose, the glycosidic bond forms between the OH on carbon 1 of one α-glucose and the OH on carbon 4 of the other.

• A disaccharide has one glycosidic bond; a polysaccharide has many glycosidic bonds.
• Each glycosidic bond formed removes one molecule of water, so the formula of the product is the monosaccharide formulae added together minus one H₂O for each bond.
• Hydrolysis of a disaccharide breaks the glycosidic bond and releases its two monosaccharides.

α-glucose and β-glucose

• α-glucose and β-glucose are isomers.
• They differ in the position of the hydrogen and hydroxyl groups on carbon atom 1, which are inverted: 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.