B4 | Biological Molecules

• Most of the molecules in living organisms fall into three categories: carbohydrates, proteins and lipids
• 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)
• 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
• 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
• • DNA, or deoxyribonucleic acid, is the molecule that contains the instructions for the growth and development of all organisms
  • It consists of two strands of DNA wound around each other in what is called a double helix
• The individual units of DNA are called nucleotides
• A nucleotide

  • 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)
• DNA base pairs

  • 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
• • DNA, or deoxyribonucleic acid, is the molecule that contains the instructions for the growth and development of all organisms
  • It consists of two strands of DNA wound around each other in what is called a double helix

  A) helix

  B) sna strand

  C) chromosomes

  D) protein

  
• • The individual units of DNA are called nucleotides

  A) phosphate

  B) deoxyribose sugar

  C) 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)

  A) base pair

  
• • 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
  • It is this sequence of bases that holds the code for the formation of proteins