CIE IGCSE Biology: 复习笔记：4.1.1 Chemicals & Life

• 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

Carbohydrates

• Long chains of simple sugars
• Glucose is a simple sugar ( a monosaccharide)
• When 2 glucose molecules join together maltose is formed (a disaccharide)
• When lots of glucose molecules join together starch, glycogen or cellulose can form (a polysaccharide)

Glycogen, cellulose and starch are all made from glucose molecules

Fats

• Most fats (lipids) in the body are made up of triglycerides
• Their basic unit is 1 glycerol molecule chemically bonded to 3 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)

Structure of a triglyceride

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

General amino acid structure

Amino acids join together to form proteins

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