Biological molecules

• Covalent bonding


  Atoms share electrons to make two full outer shells
• Ionic bonding


  Ions with opposite charges attract (electrostatic attraction) and transfer electrons
• Hydrogen bonding


  The electrons in a molecule are not evenly distributed so one position might be more negatively charged than another. This molecule is called a polar molecule. A negatively charged one and a positively charged one attract to make a weak electrostatic bond
• Polymerisation and the formation of macromolecules

  Monomers can be linked together to form long chains to form polymers
• Condensation reactions

  During polymerisation, each time a new sub-unit is attached a molecule of water is formed
• Hydrolysis reactions

  Water molecules that are used to break up bonds
• Metabolism


  The chemical processes that take place in living organisms
• Moles

  Unit for measuring the amount of a substance
• Molar solution

  A solution that has one mole of solute in each litre of solution
• Atoms

  The smallest units of chemical elements that can exist independently
• Atoms

  • Comprise a nucleus that has particles (protons and neutrons)
  • Hydrogen is the only exception
• Neutrons

  Occur in nucleus, have same mass as protons but no charge
• Protons


  In nucleus and have positive charge
• Electrons

  Orbit in shells around the nucleus. Negatively charged
• Atomic number


  Number of protons
• Mass number

  Protons and neutrons
• Isotopes


  The number of neutrons is different in two atoms of the same element
• Formation of ions


  If an atom loses or gains an electron it becomes an ion
• Positive ion


  Formed by the loss of an electron
• Negative ion


  Formed by gaining an electron
• Carbon easily forms bonds with other carbons which allow for a sequence of carbon atoms of different lengths to build up, this forms a backbone
• Carbon containing molecules are known as organic molecules. In living organisms, there are relatively few other atoms that attach to carbon so life is based on a small number of chemical elements
• Monomer


  Individual molecules that make up chains e.g., monosaccharides, amino acids
• Polymer


  Monomers joined together e.g., proteins, carbohydrates
• Saccharide


  Basic monomer unit, also known as sugar
• Monosaccharide


  A single monomer
• Disaccharide


  A pair of monosaccharides joined together
• Polysaccharide


  Multiple monosaccharides joined together
• Monosaccharides


  Sweet-tasting, soluble substances that have the formula (CH2O)n (n can be anything from 3-7)
• Monosaccharides


  • Glucose, galactose, fructose
• Glucose


  Hexose (6 carbons) sugar and has the formula C6H12O6. It has two isomers (same chemical formula but different arrangement of atoms), alpha glucose and beta glucose
• Testing for reducing sugars

  1. Add 2cm^3 of the food sample to be tested to a test tube, grind it up until it is liquid

  2. Add an equal volume of benedicts solution

  3. Boil till it hits 95 degrees in a water bath

  4. If it is a reducing sugar, it should change colour to either green, orange, red or yellow
• Making a reducing sugar

  1. Heat the sample with hydrochloric acid till it boils

  2. Neutralize the solution with sodium hydrogen carbonate and check with universal indicator

  3. Do the original test
• Disaccharides

  Formed when two monosaccharides join
• Disaccharides


  • Alpha glucose + alpha glucose = maltose
  • Glucose + fructose = sucrose
  • Glucose + galactose = lactose
• Disaccharide formation


  When the monosaccharides join, they lose a water molecule so it's a condensation reaction. This forms a glycosidic bond
• Disaccharide hydrolysis

  When water is added to a disaccharide, the bond breaks
• Starch

  A polysaccharide found in plants in the form of small grains. It forms an important component of food and is the major energy source in most diets
• Starch


  • Made up of alpha-glucose chains that are linked by glycosidic bonds that are formed by condensation reactions
  • The chain can be branched or unbranched, the unbranched chain is in a tight coil that makes the molecule compact
  • Insoluble in water and doesn't affect water potential so it doesn't allow water to go in via osmosis, causing the cell to swell making them good for storage
• Amylose


  Long, unbranched chain of a-glucose. The angles of glycosidic bonds give it a coiled structure to make it compact which is good for storage as it can fit more in more space