Biological molecules

• Most carbohydrates are polymers
• Polymers are long chains of monomers
• Monomers are basic molecular units
• this is alpha glucose

  
• This is a beta glucose

  
• Glucose + glucose = maltose

  glucose + fructose = sucrose

  glucose + galactose = lactose
• A disaccharide is created when two monosaccharides are joined together
• Polymers can be broken down into monomers by hydrolysis
• Benedict’s test for sugars

  1. Add Benedict’s reagent to a sample and heat up in a water bath
  2. If the test is positive it will form a coloured participate where the colour changes from blue to either green, yellow, orange, or brick red
  3. the higher the concentration of sugar the further the colour change goes and this can be used to compare the amount of reducing sugar
• if there is a negative result for reducing sugars then there could still be a non reducing sugar present and so a non reducing test needs to be done
• Non reducing sugar test

  1. Get a new sample of test solution and add dilute hydrochloric acid and carefully heat up in a water bath and this will break down the sugars into monosaccharides
  2. then neutralise the solution with sodium hydrogen carbonate and then carry out the benedicts test out normally
  3. positive = coloured participate same as reducing sugars but negative = remains blue
• A polysaccharide is formed when more than 2 monosaccharides are joined together by condensation reactions.
• Cells get their energy from glucose and plants store excess glucose as starch
• When a plant needs more glucose it breaks down starch which releases glucose
• Starch is made up of two polysaccharides: amylose and amylopectin
• examples of monosaccharides are amino acids and nucleotides
• Common monosaccharides are glucose, galactose and fructose
• Glycogen and starch are formed by the condensation of alpha glucose
• cellulose is made by the condensation reaction of beta glucose
• Starch and glycogen are both branched but have different structures.
• Starch can be compact and is insoluble in water so doesn’t affect the water potential and so doesn’t cause water to enter cells by osmosis.
• Animals get their energy from glucose as well but store excess as glycogen which is another polysaccharide of alpha glucose.
• Glycogen has a similar structure to starch but it has more side branches and this means that that glucose can be released quickly which will help with the energy release in animals. Glycogen is also more compact than starch
• Celluslose is made of a long unbranched chains that are made up from beta glucose
• cellulose chains are linked together by hydrogen bonding and this forms microfibrils and this allows for cellulose to provide structural support
• Triglycerides are made up of one glycerol and three fatty acids.
• Triglycerides are formed by condensation reaction and this forms a ester bond and this needs to happen three times
• saturated fatty acids dont have any double bonds between carbon atoms
• Unsaturated fatty acids have at least one double bond between carbon atoms.
• Phospholipids are similar to triglycerides but have a phosphate group which has replaced one of the fatty acids and so is made up of one glycerol, two fatty acids and one phosphate group
• The phosphate group if hydrophilic and the fatty acid tail is hydrophobic and this allows them to make up the bilayer of cell membranes.
• The centre of the bilayer is hydrophobic so water soluble substances can’t easily pass through and so the membrane acts as a barrier to those substances
• Triglycerides are mainly used as energy storage molecules and are well adapted by: long hydrocarbon tail which releases a lot of energy when broken and they are insoluble so don’t affect water potential of the cell so water can’t enter in by osmosis
• Food test for lipids:

  1. Add the test solution into a test tube and add ethanol and then shake
  2. then add water into the solution and shake again
  3. positive results = white emulsion and negative = remains clear
• • the monomers of proteins are amino acids, which are linked together by peptide bonds
  • a dipeptide is formed when two amino acids join together
  • a polypeptide is formed when more than two amino acids join together
  • proteins are made up of one or more polypeptides
• Amino acids have the same general structure of the amine and carboxyl group but the variable group (or R group) changes for each amino acid

  
• Amino acids are the building blocks of proteins and are the basic units of amino acids.
• amino acids are linked together by condensation reactions which will form polypeptides and this releases water and creates a peptide bond between the amino acids
• primary structure - is the sequence of amino acids in the polypeptide chain
• secondary structure - hydrogen bonds form between amino acids in the chain and this makes either a alpha helix or a beta pleated sheet