biology

• Inorganic ions and their biological roles

  • Magnesium (Mg2+) - Constituent of chlorophyll and essential for photosynthesis
  • Iron (Fe2+) - Constituent of haemoglobin, which transports oxygen in red blood cells
  • Nitrate (NO3-) - Nitrogen derived from nitrate is needed for making nucleotides, including ATP, DNA and RNA. Nitrogen is also needed for amino acid formation.
  • Phosphate (PO43-) - Used for making nucleotides, including ATP, DNA and RNA. A constituent of phospholipids found in biological membranes. Hardens bones.
  • Calcium (Ca2+) - Hardens bones and teeth (not strengthen). Also a component of plant cell walls.
• Organic


  Molecules that have a high proportion of carbon and hydrogen atoms
• Inorganic


  A molecule or ion that has no more than one carbon atom
• All organisms need inorganic ions to survive; these inorganic ions are often called minerals
• Micronutrients


  Minerals needed in minute (trace) concentrations e.g. copper and zinc
• Macronutrients


  Minerals needed in small concentrations e.g. magnesium and iron
• Dipole


  A polar molecule which has a positive and negative charge, separated by a very small distance
• Hydrogen bond


  The weak attractive force between a hydrogen atom (with a partial positive charge) and an atom with a partial negative charge, usually oxygen or nitrogen
• Individually hydrogen bonds are weak, but many hydrogen bonds (between many water molecules) form a lattice-like framework which is much stronger
• Cohesion


  The attraction between water molecules
• Properties of water and their functions

  • Water is a solvent
  • Water as a transport medium
  • Chemical reactions take place in water
  • Water has a high specific heat capacity
  • Water has a high latent heat of vaporisation
  • Cohesion
  • Surface tension
  • Density
• Triose


  Important in metabolism. Triose sugars are intermediates in the reactions of respiration and photosynthesis
• Pentose


  Constituents of nucleotides e.g. deoxyribose in DNA, ribose in RNA, ATP and ADP
• Hexose


  Glucose is a hexose sugar. Glucose is a source of energy in respiration. Carbon-hydrogen and carbon-carbon bonds are broken to release energy, which is transferred to make adenosine triphosphate (ATP)
• Carbohydrates are organic compounds which contain the atoms carbon, hydrogen and oxygen
• The basic unit of a carbohydrate is a monosaccharide
• Two monosaccharides form a disaccharide
• Many monosaccharide molecules form a polysaccharide
• A polysaccharide is a type of polymer
• Monosaccharides are sweet and soluble
• Monosaccharides are the building blocks for the other larger carbohydrates
• Monosaccharides have the general formula (CH2O)n and they can be grouped according to the number of carbon atoms they have
• Isomers


  Have the same chemical formula and the same number of atoms; the atoms are simply arranged differently
• The ring form of the monosaccharide glucose has two isomers α glucose and β glucose
• α glucose and β glucose have the same chemical formula C6H12O6, but the H and OH atoms are arranged differently at carbon 1
• Disaccharides


  Composed of two monosaccharide sub-units bonded with the formation of a glycosidic bond and the elimination of water
• Condensation reaction


  Water is chemically removed to form a bond between adjacent monomers
• Hydrolysis


  Water is chemically added to break a bond between monomers
• Disaccharides and their component monosaccharides

  • Maltose - Glucose and Glucose
  • Sucrose - Glucose and Fructose
  • Lactose - Glucose and Galactose
• Benedict's reagent is used to test for reducing sugars
• Reducing sugars reduce blue copper ll sulphate forming copper l sulphate, which is a brick red precipitate
• Examples of reducing sugars include all the monosaccharides and the disaccharides lactose and maltose
• Sucrose is called a non-reducing sugar because it does not reduce copper ll sulphate
• Testing for non-reducing sugars like sucrose

  1. Sucrose must first be hydrolysed by boiling in dilute hydrochloric acid

  2. Glucose and fructose are formed

  3. The acid must be neutralised with dilute sodium hydroxide before testing with Benedict's reagent

  4. This should now give a positive result; glucose and fructose are reducing sugars which readily donate an electron to reduce copper II sulphate to form the brick-red precipitate copper I sulphate
• Polysaccharides


  Large complex polymers formed from very large numbers of identical monosaccharide units, which are their monomers, linked by glycosidic bonds formed by condensation reaction
• Starch


  Allows plants to store glucose. Starch is made up of α glucose monomers, added one at a time by condensation reaction. Glucose can be easily added or removed. Starch has two types of polysaccharide, amylose and amylopectin
• Amylose


  Unbranched and coiled; each α glucose monomer added forms a C1 – C4 glycosidic bond with the adjacent glucose molecule
• Amylopectin


  Branched as it forms C1 - C4 gylcosidic bonds and C1 – C6 glycosidic bonds
• Starch is compact and has no osmotic effect on the cell; it does not affect the water potential of the cell
• Glycogen


  The main storage product in animals. It is similar in structure to amylopectin, but has shorter C1 – C4 α glucose chains and more C1 – C6 branch points, making it more branched than amylopectin