4.Biological molecules

• Most of the molecules in living organisms fall into three categories: carbohydrates, proteins and lipids
• carbohydrates, proteins and lipids all contain carbon and so are described as organic molecules
• molecule: carbohydrate

  chemical elements: carbon,oxygen and hydrogen
• molecule: protein

  chemical elements: all contain carbon,oxygen,nitrogren and hydrogen. some contain small amounts of other elements such as sulphur
• 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)
• 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
• Amino acids join together to form proteins, which are the building blocks of cells.

  
• Test for glucose (a reducing sugar)

  • Add Benedict's solution into sample solution in test tube
  • Heat at 60 - 70 °c in water bath for 5 minutes
  • Take test tube out of water bath and observe the colour
  • A positive test will show a colour change from blue to orange or brick red
•  Test for starch using iodine

  • We can use iodine to test for the presence or absence of starch in a food sample.
• The iodine test for starch

  • Add drops of iodine solution to the food sample
  • A positive test will show a colour change from orange-brown to blue-black
• Test for protein

  • Add drops of Biuret solution to the food sample
  • A positive test will show a colour change from blue to violet / purple
• Test for lipids

  • Food sample is mixed with 2cm3 of ethanol and shaken
  • The ethanol is added to an equal volume of cold water
  • A positive test will show a cloudy emulsion forming
• Test for vitamin C

  • Add 1cm3 of DCPIP solution to a test tube
  • Add a small amount of food sample (as a solution)
  • A positive test will show the blue colour of the dye disappearing
• DNA, or deoxyribonucleic acid, is the molecule that contains the instructions for the growth and development of all organismsIt consists of two strands of DNA wound around each other in what is called a double helix
• DNA, chromosomes and the nucleus

  
• the individual units of DNA are called nucleotides

  
• • All nucleotides contain the same phosphate and deoxyribose sugar, but differ from each other in the base attached
  • There are four different bases, Adenine (A), Cytosine (C), Thymine (T) and Guanine (G)
  • The bases on each strand pair up with each other, holding the two strands of DNA in the double helix
  • The bases always pair up in the same way:
  • Adenine always pairs with Thymine (A-T)
  • Cytosine always pairs with Guanine (C-G)
• the phosphate and sugar section of the nucleotides form the ‘backbone’ of the DNA strand (like the sides of a ladder) and the base pairs of each strand connect to form the rungs of the ladder