Proteins, fats and carbs

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  • Proteins, fats and carbohydrates
    • Proteins
      • Proteins consist of one or more polypeptides arranged as complex macromolecules. They have specific biological functions. All proteins contain the elements; carbon, hydrogen, oxygen and, nitrogen.
      • Amino acids - the monomers - all have the same basic structure; an amine group, a carboxyl group and, an R group. Different R groups result in different amino acids, which there are twenty commonly found in cells.
        • Amino acids bond when the amine group and the carboxylic group react.
          • The hydroxyl in the carboxylic group of one amino acid reacts with a hydrogen of the amine group of another amino acid. A peptide bond is formed between the amino acids and water is produced. This is a condensation reaction.
      • Biuret solution is used to identify the presence of protein. Biuret reagent is a blue solution that, when it reacts with protein, will change color to pink-purple.
    • Fats (lipids)
      • Fats are large, complex molecules known as macromolecules. They are not built from monomers. Fats contain the elements; carbon, hydrogen and, oxygen.
        • Glycerol is an alcohol. Fatty acids are carboxylic acids - consisting of a carboxylic group with a hydrocarbon chain attached.
      • Sudan III is used to identify the presence of lipids in liquids. It will stain fat cells red.
      • Triglycerides are made by combining one glycerol molecule with with 3 fatty acids.
        • Both molecules contain hydroxyl groups which interact, forming 3 water molecules and bonds between the fatty acid and glycerol. These are ester bonds and the process is called esterification - a condensation reaction.
      • Phospholipids are modified triglycerides and contain a phosphate group, replacing one of the fatty acid groups.
    • Carbohydrates
      • A single carbohydrate (saccharide or sugar) is a monosaccharide. When 2 of these monosaccharides link together, they are called a disaccharide. Polysaccharides are long chains of monosaccharides bonded together.
      • The monomers of carbohydrates are glucose molecules. Glucose is a hexose monosaccharide.
        • There is alpha and beta glucose, in which the hydroxyl (OH) group on carbon 1 is in opposite positions.
      • When 2 alpha glucose molecules are side by side, the hydroxyl groups react. From this, a water molecule is formed and a bond forms between carbons 1 and 4 on the glucose molecules. They are now joined.
        • A covalent bond called a glycosidic bond is formed. The reaction is a condensation reaction and the bond formed is known as a 1,4 glycosidic bond. This has formed a disaccharide.
      • There are 3 chemical tests which can be done to test for the presence of a carbohydrate.
        • Reducing sugars react with the copper in Benedict's reagent. When a reducing sugar is mixed with Benedict's reagent and warmed, a brick-red precipitate is formed.
        • Non-reducing sugars must first be boiled with dilute hydrochloric acid to give a positive result when warmed with Benedict's solution. The colour change will be the same as in the reducing sugars test.
        • The iodine test is done to test for starch. Iodine dissolved in potassium iodide solution is mixed with a sample. If the solution changes from yellow/brown to purple/black, then starch is present in the sample.

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