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
• fill in the blanks

  A) carbon

  B) oxygen

  C) hydrogen

  D) carbon

  E) oxygen

  F) hydrogen

  G) nitrogen

  H) carbon

  I) oxygen

  J) hydrogen

  
• 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

  A) glycerol

  B) 3 fatty acid tails

  
• 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

  
• Food 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 
• Food 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

  A) blue-black colour change

  B) no color change

  
• Food 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

  
• Food 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

  A) cloudy emulsion

  
• Food 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

  
• When describing food tests in exam answers, make sure you give the starting colour of the solution and the colour it changes to for a positive result.
• DNA (deoxyribonucleic acid)


  The molecule that contains the instructions for the growth and development of all organisms
• A DNA molecule consists of two strands of DNA wound around each other in what is called a double helix
• DNA, chromosomes and the nucleus

  A) dna double helix

  B) dna

  C) proteins

  D) strand

  E) chromosomes

  
• A chromosome is a long strand of DNA wrapped around proteins
• The individual units of DNA are called nucleotides
• The individual units of DNA are called nucleotides

  A) backbone

  B) phosphate

  C) deoxyribose sugar

  D) base

  
• • 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

  
• The DNA helix is made from two strands of DNA held together by hydrogen bonds. It is this sequence of bases that holds the code for the formation of proteins
• You do not need to learn the names of the nucleotide bases, just their letter. Make sure you know which bonds with which, as this is the most commonly asked question about this topic.