Biological Molecules PDF

Unit 4 - Biological molecules 4.1 Chemicals & Life Chemical Elements Most of the molecules in living organisms fall into three categories: carbohydrates, proteins and lipids These all contain carbon and so are described as organic molecules Molecule Chemical...

Unit 4 - Biological molecules 4.1 Chemicals & Life Chemical Elements Most of the molecules in living organisms fall into three categories: carbohydrates, proteins and lipids These all contain carbon and so are described as organic molecules Molecule Chemical elements Carbohydrate Carbon, oxygen and hydrogen Protein All contain carbon, oxygen, hydrogen and nitrogen and some contain small amounts of other elements such as sulphur Lipid Carbon, oxygen and hydrogen 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) 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 4.2 Food tests Food tests in biology 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 We can use iodine to test for the presence or absence of starch in a food sample. Add drops of iodine solution to the food sample A positive test will show a colour change from orange-brown to blue-black 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 2cm of ethanol and shaken The ethanol is added to an equal volume of cold water A positive test will show a cloudy emulsion forming Food test for vitamin C Add 1 cm 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 4.3 DNA Structure Structure of a DNA Molecule (Extended) DNA, or deoxyribonucleic acid, is the molecule that contains the instructions for the growth and development of all organism 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 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 It is this sequence of bases that holds the code for the formation of proteins