Biological Molecules

• What is a monomer?

  Small, basic molecular units that can form a polymer. E.g, monosaccharides, amino acids and nucleotides.
• What is a polymer?

  Large, complex molecule composed of long chains of monomers joined together. E.g, proteins, nucleic acids and most carbohydrates.
• What is a condensation reaction?

  Forms polymer by joining 2 monomers together with formation of glycosidic bond and elimination of a water molecule.
• What is a hydrolysis reaction?

  Breaks down polymer into its monomers by breaking glycosidic bond between monomers, using water molecule.
• Why are biological molecules evidence for evolution?

  All organisms share some biochemistry, e.g, same nucleic acids as genetic material and same amino acids to build proteins. Similarities suggest animals and plants have common ancestor.
• What are sugars?

  General term for monosaccharides and disaccharides.
• What are monosaccharides?

  Simplest sugars. Make carbohydrates. E.g, glucose, fructose and galactose.
• What are the 2 isomers of glucose?

  Alpha and beta. Same molecular formula, different arrangement of atoms. Beta glucose- right OH on top.
• How is maltose made?

  Glucose + glucose.
• How is lactose made?

  Glucose + galactose.
• How is sucrose made?

  Fructose + glucose.
• How would you test for reducing sugars?

  Reducing sugars are all monosaccharides and some disaccharides, e.g lactose & maltose. Heat sample with Benedict's reagent. Positive result- coloured precipitate forms (green, yellow, orange, brick-red). Negative result- sample stays blue.
• How would you test for non-reducing sugars?

  E.g, sucrose. Add dilute HCL to new sample and heat. Neutralise with sodium hydrogen-carbonate. Carry out normal Benedict's test. Positive result- coloured precipitate forms. Negative- sample stays blue.
• What are polysaccharides?

  Carbohydrates. Formed when more than 2 monosaccharides joined.
• What is the structure of starch?

  Mix of 2 polysaccharides of alpha glucose- amylose and amylopectin. Plants store excess glucose as starch.
• What is the structure of amylose?

  Long, unbranched chain of alpha glucose. Angles of glycosidic bonds give it coiled structure (cylindrical). Hydrogen bonds between alpha glucose hold amylose in helical structure. Makes it compact & good for storage.
• What is the structure of amylopectin?

  Long, branched chain of alpha glucose. Side branches allow enzymes that breakdown molecule to get to glycosidic bonds easily, so glucose released quickly. Insoluble in water & doesn't affect water potential, so doesn't cause water to enter cells via osmosis and swell. Large molecule so can't leave cell.
• What is the structure of glycogen?

  Animals store excess glucose as this. Polysaccharide of alpha glucose, similar structure to amylopectin, has more side branches, so glucose released quickly. Compact molecule. Insoluble in water.
• What is the structure of cellulose?

  Long, unbranched chains of beta glucose. When beta glucose molecules bond, form straight cellulose chains. Chains linked together by hydrogen bonds, forming strong fibres called microfibrils. Cellulose provides structural support for cells, e.g, plant.
• How could you compare amount of reducing sugar in different solutions?

  Compare colour change. Filter each solution and weigh precipitate. Remove precipitate and use colorimeter to measure absorbance of remaining Benedict's reagent.
• How do you test for starch?


  Add iodine dissolved in potassium iodide solution to sample. Positive result- sample changes from browny-orange to a dark, blue-black colour.
• What is the structure of a triglyceride?


  1 molecule of glycerol with 3 fatty acids attached to it. Fatty acid molecules have long tails made of hydrocarbons. Tails are hydrophobic, making lipids insoluble in water.
• What is the structure of saturated fatty acids?

  Don't have any double bonds between carbon atoms in hydrocarbon tail.
• What is the structure of unsaturated fatty acids?

  Have double bonds between carbon atoms in hydrocarbon tail.
• How are triglycerides formed?

  Condensation reactions. Fatty acid joins glycerol molecule. Ester bond forms between the 2 molecules, releasing H20 molecule. Happens 3 times to form triglyceride.
• What is the structure of phospholipids?

  Similar to triglycerides but 1 fatty acid molecule replaced by phosphate group. Phosphate group hydrophilic. Fatty acid tails hydrophobic.
• What are the properties of triglycerides?

  Energy storage molecules as long hydrocarbon tails of fatty acids contain lots of chemical energy, so lots of energy released when broken down. Insoluble in water and doesn't affect water potential of cell. Bundle together as insoluble droplets in cells as fatty acid tails are hydrophobic-tails face inwards, sheltering themselves from water with their glycerol heads.
• What are the properties of phospholipids?

  Make bilayer of cell membranes. Heads hydrophilic & tails hydrophobic, so form double layer. Centre of bilayer hydrophobic- water-soluble substances can't easily pass through.
• What is the emulsion test for lipids?

  Shake test substance with ethanol for 1 min. Pour solution into water. Positive result- milky emulsion forms.
• What is the general structure of an amino acid?

  Carboxyl group (COOH), amine group (NH2) and R group.
• How many amino acids are there?

  20- difference between them is their R groups.
• What is the primary structure of a protein?

  Sequence of amino acids in polypeptide chain.
• What is the secondary structure of a protein?

  Hydrogen bonds form between amino acids in chain. Makes it coil into alpha helix or fold into beta pleated sheet.
• What is the tertiary structure of a protein?

  Coiled or folded chain of amino acids often coiled & folded further. More bonds form between different parts of polypeptide chain, including hydrogen bonds & ionic bonds. Disulfide bridges form whenever 2 molecules of amino acid cysteine come close together. Final 3D structure for protein with 1 polypeptide chain.
• What is the quaternary structure of a protein?

  Proteins made of several different polypeptide chains, held together by bonds. E.g, hb, insulin and collagen.
• Shape & function of hb?

  Compact, soluble protein, so easy to transport and carry O2 around body.
• Shape & function of enzymes?

  Roughly spherical shape due to tight folding of polypeptide chains. Soluble and often have roles in metabolism, e.g, digestive systems.
• Shape & function of antibodies?

  Found in blood- involved in immune response. 2 light (short) chains and 2 heavy (long)chains bonded together. Have variable regions- amino acid sequence vary greatly here.
• Shape & function of transport proteins?

  Channel proteins in cell membranes- contain hydrophobic & hydrophilic amino acids. Cause protein to fold up and form a channel. Transport molecules and ions across membranes.
• Shape & function of structural proteins?


  Physically strong- long polypeptide chains lying parallel to eachother with cross-links to eachother. E.g, keratin and collagen (found in connective tissue). Collagen has 3 chains tightly coiled together.