Unit 1- Digestive system (2)

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  • Unit 1- Digestive system
    • Proteins
      • Made from long chains of Amino Acids. Monomers of proteins are amino acids, dipeptide is formed when two amino acids join together, a polypeptide is formed when more then two amino acids join together. Proteins are made up of one of more polypeptides.
      • All amino acids have the same general structure. Carboxyl group (-COOH) and an amino group (-NHv2) attatched to a carbon atom. The difference between amino acids is the variable group (-R) that they contain.
      • Primary structure: sequence of amino acids in the polypeptide chain. Secondary structure: hydrogen bonds form between amino acids in the chain, this automatically makes it coil into alpha helix or fold into a beta pleated sheet. Tertiary strusture: the coilded or folded chain of amino acids is coiled and folded further. More bonds between different parts of the polypeptide chain are formed. For proteins made of a single polypeptide shain, this is their final structure. Quaternary structure: proteins made of several different polypeptide chains are held together by bonds. This is the final structure of a protein that has more that one polypeptide chain.
      • Biuret Test: 1) the test solution needs to be alkaline, so firts add a few drops of sodium hydroxide solution. 2) then add some copper (II) sulfate solution. If protein is present a purple layer forms. If protein is absent the solution will stay blue. The colours are pale so yo will need to loo carefully.
    • Carbohydrates
      • Most carbohydrates are polymers, all carbohydrates contain the elements C, H and O, the monomers that they're made from are monosaccharides, eg glucose, fructose and galactose. Glucose is a hexose sugar - a monosaccharide with six carbon atoms in each molecule. There are two forms of glucose, alpha and beta. Learn the structure of an alpha glucose.
      • Benedicts Test for sugars: Reducing sugars: 1) eg maltose 2) add benedicts reagent (blue) to a sample and heat it. If the sample contains reducing sugars it gradually turns brick red due to the formation of a red precipitate. Non reducing suagrs: 1) like before, break into monosaccharides. 2) boil the test solution with dilute hydrochloric acid and then neutralise it with sodium hydrogencarbonate. Then carry out benedicts test as you would for a reducing sugar. 3) if the test is possitive, it could be reducing or non reducing sugar. To check its non reducing, do the reducing sugar test too (to rule out the possibility of it being a reducing sugar.
      • Iodine test for starch: add iodine dissolved in potassium iodine solution to test the sample. if starch is present, it changed from browny-orange to a dark, blue-black colour.


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