metabolism

• Metabolism is going on all of the time.
• • In a cell there are lots of chemical reactions happening all the time, which are controlled by enzymes
  • many of these reactions are linked together to form bigger reactions
• In some reactions larger molecules are made from smaller ones, for example:

  • Lots of small glucose molecules are joined together in reactions to form starch, glycogen, and cellulose.
  • Lipid molecules are each made from molecules of glycerol and three fatty acids
  • Glucose is combined with nitrate ions to make amino acids, which are then made into proteins
• In other reactions, larger molecules are broken down, for example:

  • Glucose is broken down in respiration. Respiration transfers energy to power all the reactions in the body that make molecules.
  • Excess protein is broken down in a reaction to produce urea. Urea is then excreted in urine.
• The sum of all reactions that happen in a cell or the body is called its metabolism