B3: Biological Molecules

Carbohydrates, Fats, Proteins

Carbohydrates

  • The main source of energy of the body
  • Made up of carbon, hydrogen, and oxygen
  • Glucose (C₆H₁₂O₆) is a simple sugar
  • A chain of glucose creates larger molecules, such as starch or glycogen


Fats

  • Provide energy
  • Absorbs some vitamins
  • Made up of carbon, hydrogen, and oxygen
  • Most fats are made by triglycerides (units of a glycerol molecule chemically bonded with 3 chains of fatty acids)


Proteins

  • Used to build and repair tissues
  • Used for extra energy and to fight infection
  • All contain carbon, hydrogen, oxygen, and nitrogen
  • Some contain other elements
  • Proteins are made up of chains of amino acids
  • There are 20 types of amino acids
  • A difference in which the amino acids are ordered in a bond will cause a different protein to be formed


Biological Molecule Indicator Test

There are different ways to test for the presence of biological molecules in substances. This is through the use of indicators. Drops of the indicator will be mixed into the substance, which will change the colour or cause a cloudy emulsion and indicate the presence of a molecule

  • Iodine solution
    • When starch is present, the colour is black
    • When starch is not present, the colour is dark red
  • Benedict's solution (tests for simple sugars)
    • When simple sugars are present, the colour is orange
    • When simple sugars are not present, the colour is blue
  • Biuret solution (tests for proteins)
    • When proteins are present, the colour is violet/black
    • When proteins are not present, the colour is blue
  • The ethanol test (tests for fats and oils) is a bit different. After shaking the ethanol with the substance, you need to add the mixture into cold water of an amount of the equal volume
    • When fats and oils are present, there will be a cloudy layer formed
    • When fats and oils are not present, there will not be a cloudy layer formed


The importance of water as a solvent
  • Many substances can dissolve into water
  • Dissolved substances are transported easily through organisms
  • Toxic substances (eg. urea and salts) are removed from the body after dissolved into water in urine
  • Water makes up a big part of the cytoplasm to make sure that metabolic reactions happen in cells


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