Monomers, sugars and Benedict's test

Last time

Before we start: last time, in Amino acids, protein structure, haemoglobin and collagen, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Lego for living things

Big biological molecules are built like a Lego model. Small repeating bricks, called monomers, join in long chains. The joined chain is a polymer. Starch, protein and D N A are all built this way, and the sugar bricks come first.

Monomers, polymers, macromolecules

A monomer is a small molecule that can join with others. Glucose, amino acids and nucleotides are monomers. A polymer is a chain made of many repeating monomers. Starch, protein and D N A are polymers. A macromolecule is any very large molecule. All polymers are macromolecules, but not all macromolecules are polymers. A triglyceride is a macromolecule but not a polymer, because it is not made of repeating identical units.

Condensation and hydrolysis

Monomers join by a condensation reaction. A bond forms and one molecule of water is removed. Polymers are broken down by hydrolysis. Water is added, and the bond breaks. When two monosaccharides join, the new bond is a glycosidic bond.

Monosaccharides

Glucose, fructose and galactose are monosaccharides. Each has the formula C six H twelve O six. They are the single sugar units, the monomers that build the larger carbohydrates, and they are all soluble and sweet. Glucose exists in two forms. In alpha glucose, the hydroxyl on carbon one points down. In beta glucose, it points up. Only that one group differs, yet it changes how the molecules join. Alpha glucose makes starch and glycogen, and beta glucose makes cellulose.

Disaccharides

Maltose is glucose plus glucose. Sucrose is glucose plus fructose. Lactose is glucose plus galactose. In maltose, two alpha glucose molecules are joined by an alpha one four glycosidic bond, with water released. Adding water and breaking the bond, by hydrolysis, gives back the two monosaccharides.