Biological molecules

• Biological molecules


  Particular groups of chemicals that are found in living organisms. Their study is known as molecular biology.
• Covalent bonding


  Atoms share a pair of electrons in their outer shells, forming a stable compound called a molecule
• Ionic bonding


  Ions with opposite charges attract one another through electrostatic attraction. Ionic bonds are weaker than covalent bonds.
• Hydrogen bonding


  The uneven distribution of charge in a polarised molecule leads to a weak electrostatic bond between the negatively and positively charged regions of different molecules.
• Monomer


  Molecules that can be linked together to form long chains called polymers
• Polymer


  Long chains of monomer sub-units
• Polymerisation


  The process by which monomers are linked together to form polymers
• Condensation reaction


  Reactions that produce water when a new sub-unit is attached to a polymer
• Hydrolysis


  The breaking down of polymers through the addition of water, splitting the molecule into its constituent parts
• Metabolism


  All the chemical processes that take place in living organisms
• Mole


  The SI unit for measuring the amount of a substance, containing the same number of particles as 12g of carbon-12 atoms
• Molar solution


  A solution that contains one mole of solute in each litre of solution
• The chemical formula for sodium chloride is NaCl, which means that a molecule of sodium chloride contains one sodium atom and one chlorine atom.
• Atom


  The smallest unit of a chemical element that can exist independently
• Neutrons


  Particles in the nucleus of an atom with the same mass as protons but no electrical charge
• Protons


  Particles in the nucleus of an atom with the same mass as neutrons but a positive charge
• Electrons


  Negatively charged particles that orbit the nucleus of an atom
• Atomic number


  The number of protons in an atom
• Mass number


  The total number of protons and neutrons in an atom
• Isotopes


  Different types of the same element that have the same number of protons but different numbers of neutrons
• Ion


  An atom that has lost or gained one or more electrons, becoming positively or negatively charged
• Carbon atoms have an unusual feature - they very readily form bonds with other carbon atoms, allowing a sequence of carbon atoms of various lengths to be built up.
• Monomer


  The individual molecules that make up a polymer, including monosaccharides, amino acids and nucleotides
• Polymer


  Long chains of monomers
• Monosaccharide


  The basic unit of carbohydrates, a single sugar molecule
• Disaccharide


  Two monosaccharides combined together
• Polysaccharide


  Many monosaccharides combined together in much larger numbers
• Reducing sugar


  A sugar that can donate electrons and be reduced by another chemical, such as Benedict's reagent
• Benedict's test

  Adding Benedict's reagent (an alkaline solution of copper(II) sulfate) to a food sample, then heating. A red precipitate of copper(I) oxide forms if reducing sugars are present.
• The Benedict's test is semi-quantitative, meaning it can be used to estimate the approximate amount of reducing sugar in a sample based on the colour change.
• The differences in colour in the Benedict's test indicate the concentration of reducing sugar in the sample.
• Disaccharides


  Pairs of monosaccharides combined to form a larger molecule
• Polysaccharides


  Polymers formed by combining many monosaccharide molecules
• Formation of glycosidic bond

  1. Removal of water (condensation reaction)

  2. Addition of water (hydrolysis reaction)
• Non-reducing sugars


  Disaccharides that do not change the colour of Benedict's reagent when heated with it
• Test for non-reducing sugars

  1. Grind sample into liquid form

  2. Add sample and Benedict's reagent, heat in water bath

  3. If no colour change, add hydrochloric acid to hydrolyse

  4. Neutralise with sodium hydrogencarbonate

  5. Retest with Benedict's reagent
• Polysaccharides


  • Insoluble due to large size
  • Suitable for storage
  • Break down into disaccharides or monosaccharides when hydrolysed
• Starch


  Polysaccharide formed by joining 200-100,000 α-glucose molecules by glycosidic bonds
• Starch


  • Found in plant cells as small granules or grains
  • Major energy source in most diets
  • Insoluble so doesn't affect water potential
  • Compact so can be stored in small space
  • Easily hydrolysed to release glucose for respiration
  • Branched form has many ends that can be acted on by enzymes
• Test for starch


  1. Place sample in test tube

  2. Add iodine solution

  3. Blue-black colour indicates presence of starch