biology AS

• Monomer


  Smaller units from which larger molecules are made
• Polymer


  Molecules made from a large number of monomers joined together in a chain
• Macromolecule


  Very large molecules containing 1000 or more atoms and having a high molecular mass
• There is a massive variety of life within and between organisms, however, the biochemical basis of life is similar for all living things
• Key molecules required to build structures that enable organisms to function

  • Carbohydrates
  • Proteins
  • Lipids
  • Nucleic Acids
  • Water
• Monomers are the smaller units from which larger molecules are made
• Carbon compounds can form small single subunits (monomers) that bond with many repeating subunits to form large molecules (polymers) by a process called polymerisation
• Polymers can be macromolecules, however, not all macromolecules are polymers as the subunits of polymers have to be the same repeating units
• Covalent bond


  The sharing of two or more electrons between two atoms
• Nonpolar covalent bond


  Electrons are shared equally between atoms
• Polar covalent bond


  Electrons are shared unequally between atoms, with one atom being more electronegative
• Generally, each atom will form a certain number of covalent bonds due to the number of free electrons in the outer orbital e.g. H = 1 bond, C = 4 bonds
• Covalent bonds are very stable as high energies are required to break the bonds
• Multiple pairs of electrons can be shared forming double bonds (e.g. unsaturated fats C-C) or triple bonds
• Condensation reaction


  Monomers combine together by covalent bonds to form polymers (polymerisation) or macromolecules (lipids) and water is removed
• Hydrolysis


  Covalent bonds are broken when water is added
• Carbohydrates, lipids, proteins and nucleic acids contain the chemical elements carbon (C) and hydrogen (H) making them organic compounds
• Carbon atoms are key to organic compounds because: Each carbon atom can form four covalent bonds - this makes the compounds very stable (as covalent bonds are so strong they require a large input of energy to break them), Carbon atoms can form covalent bonds with oxygen, nitrogen and sulfur, Carbon atoms can form straight chains, branched chains or rings
• Carbohydrate


  Organic compounds containing C, H and O in the ratio 1:2:1
• Types of carbohydrates


  • Monosaccharides
  • Disaccharides
  • Polysaccharides
• Carbohydrates have many different functions: 1. Source of energy e.g. glucose is used for energy-release during cellular respiration, 2. Store of energy e.g. glycogen is stored in the muscles and liver of animals, 3. Structurally important e.g. cellulose in the cell walls of plants
• Reducing sugar


  Sugars that can donate electrons and become oxidised
• Non-reducing sugar


  Sugars that cannot donate electrons and cannot be oxidised
• Reducing sugars can be detected using the Benedict's test as they reduce the soluble copper sulphate to insoluble brick-red copper oxide
• Examples of reducing sugars: glucose, fructose, maltose, galactose
• Non-reducing sugars must first be hydrolysed to break the disaccharide into its two monosaccharides before a Benedict's test can be carried out
• Example of a non-reducing sugar: sucrose
• Forming the glycosidic bond

  Two hydroxyl (-OH) groups (on different saccharides) interact to form a strong covalent bond called the glycosidic bond, resulting in one water molecule being removed
• Breaking the glycosidic bond


  The glycosidic bond is broken when water is added in a hydrolysis reaction
• Hydrolytic reactions are catalysed by enzymes, these are different to those present in condensation reactions
• Examples of hydrolytic reactions include the digestion of food in the alimentary tract and the breakdown of stored carbohydrates in muscle and liver cells for use in cellular respiration
• Sucrose is a non-reducing sugar which gives a negative result in a Benedict's test. When sucrose is heated with hydrochloric acid this provides the water that hydrolyses the glycosidic bond resulting in two monosaccharides that will produce a positive Benedict's test
• Polysaccharide


  Macromolecules that are polymers formed by many monosaccharides joined by glycosidic bonds in a condensation reaction to form chains
• Polysaccharides


  • They can be branched or unbranched, folded (compact for storage) or straight (for structural purposes)
• Starch and glycogen


  Storage polysaccharides that are compact and insoluble
• Amylose


  Unbranched helix-shaped chain with 1,4 glycosidic bonds between α-glucose molecules
• Amylopectin


  Has 1,4 glycosidic bonds between α-glucose molecules but also 1,6 glycosidic bonds forming branches
• Glycogen


  The storage polysaccharide of animals and fungi, highly branched
• Liver and muscle cells have a high concentration of glycogen, present as visible granules, as the cellular respiration rate is high in these cells (due to animals being mobile)
• The branching in glycogen enables more free ends where glucose molecules can either be added or removed allowing for condensation and hydrolysis reactions to occur more rapidly - thus the storage or release of glucose can suit the demands of the cell