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

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

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
  • 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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