Biological molecules

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  • f212 - biological molecules
    • water
      • reactant in chemical reactions
      • solvent, substances dissolve in it
      • liquid, transports substances
      • helps with temperature control, carries away heat energy when it evaporates from a surface
      • structure
        • one atom of oxygen, joined to two atoms of hydrogen, by shared electrons
      • high specific heat capacity
        • lots of  energy is needed to raise the temperature of 1g of substance of water by 1 degree.
          • stops rapid temperature changes, allowing them to keep their temperature fairly stable
      • high latent heat of evaporation
        • lots of energy is needed to break the hydrogen bonds between the water molecules
          • great for cooling things
      • polarity
        • cohesive - helps water to flow, good for transporting things
        • good solvent  - other polar molecules will dissolve it in
    • proteins
      • made from long chains of amino acids
        • dipeptide - 2 amino acids joined together
        • polypeptide - more than 2 amino acids joined together
        • structure
          • all amino acids have the same general structure
            • carboxyl group (-COOH)
            • amino group (-NH2)
            • variable group (R)
        • held together by peptide bonds
          • condensation reaction = molecule of water is released
          • hydrolysis = a molecule of water is added to break the peptide bond
      • structural levels
        • primary structure
          • sequence of amino acids in the polypeptide chain
            • peptide bonds
          • secondary structure
            • hydrogen bonds form between the amino acids in the chain. coils/folds in to a alpha helix or beta pleated sheet
              • hydrogen bonds
            • tertiary structure
              • coiled/folded further. proteins made of a single polypeptide chain = final 3D shape
                • ionic interactions, disulfide bonds, hydrophobic and hydrophillic interactions, hydrogen bonds
              • quaternary structure
                • the way the polypeptide chains are assembled together = final 3D shape for proteins made from more than one polypeptide chain
                  • same as tertiary structure
      • collagen
        • fibrous protein, forms supportive tissue in animals
        • made of 3 polypeptide chains coiled into a triple helix, interlocked by covalent bonds
        • minerals bind to triple helix to increase rigidity
      • haemoglobin
        • globular protein, iron containing haem group that binds to oxygen, carrying it around the body
        • curled up structure, hydrophillic side chains on the outside, hydrophobic side chains on the inside = soluble in water, so good for transport in the blood
    • carbohydrates
      • made from monnosaccharides
        • monnosaccharides join together to form disaccharides and polysaccharides
          • joined together by glycosidic bonds
            • during synthesis, a hydrogen atom on one monnosaccharide bonds to a hydroxyl group on the other, releasing a molecule of water
      • polysaccahrides
        • starch - main energy storage material in plants
          • cells get energy form glucose, plants store excess glucose as starch
            • when a plant needs more glucose for energy, it breaks down starch to release glucose
        • glycogen - main energy storage material in animals
          • animals store excess glucose as glycogen
            • similar structure to amylopectin, loads more side branches, so stored glucose can be released quickly, important for energy release in animals
              • compact molecule, good for storage
        • cellulose - major component of cell walls in plant
          • long, unbranched chains of b-glucose
            • bonds between sugars are straight, so cellulose chains are straight
              • linked together by hydrogen bonds, to form strong fibres called  microfibrils
                • strong fibres = structural support for cells
    • lipids
      • triglycerides
        • one molecule of glycerol, attached to 3 fatty acid tails
          • tails are hydrophobic, so lipids are insoluble in water
            • joined  by an ester bond
              • bundle together in insoluble droplets,
      • phospholipids
        • found in cell membranes
          • one molecule of glycerol, attached to 2 fatty acid tails and a phosphate group
            • hydrophillic head, hydrophobic tail
              • bilayer of cell membranes , acts as a barrier to substances
      • cholesterol
        • found in cell membranes
          • hydrocarbon ring attached to a hydrocarbon tail
            • soluble in water, insoluble in water, so is carried around the body by proteins called lipoproteins
              • small flattened shape allows it to fit in between phospholipid molecules causing them to pack closely together, making the membrane less fluid and more rigid
    • biochemical test for molecules
      • reducing sugars
        • add benedicts solution, heat to 80 degrees
          • if positive, colour change from blue to orange/red
      • non-reducing sugars
        • boil solution with dilute hydrochloric acid
          • cool, and neutralize with sodium hydrocarbonate
            • add benedicts solution, heat to 80 degrees
              • positive result = non-reducing sugar negative result = no non reducing sugar/reducing sugar
      • starch
        • add iodine solution
          • if starch is present, colour change to blue/black, if not colour stays orange/brown
      • protein
        • add sodium hydroxide
          • add copper sulfate solution
            • if protein is present, purple layer forms
              • if there's no protein, solution stays blue
      • lipids
        • shake test substance with ethonal
          • pour into test tube with water
            • if lipid is present, a milky white precipitate will form

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