Chemicals & Life (Cambridge (CIE) IGCSE Combined Science: Biology): Revision Note

Chemical elements

• Most of the molecules in living organisms fall into three categories: carbohydrates, proteins and lipids

• These all contain carbon and so are described as organic molecules

Chemical elements table

Large molecules are made from smaller molecules

Carbohydrates

• Long chains of simple sugars (monosaccharides)

• Glucose is a simple sugar

• When two glucose molecules join together maltose is formed (a disaccharide)

• When lots of glucose molecules join together starch, glycogen or cellulose can form (a polysaccharide)

Fats

• Most fats (lipids) in the body are made up of triglycerides

• Their basic unit is one glycerol molecule chemically bonded to three fatty acid chains

• The fatty acids vary in size and structure

• Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature)

Proteins

• Long chains of amino acids

• There are about 20 different amino acids

• They all contain the same basic structure but the ‘R’ group is different for each one

• When amino acids are joined together a protein is formed

• The amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins

• Even a small difference in the order of the amino acids results in a different protein being formed