M2:S2 Biological molecules

• Water


  One of the most important substances on the planet, vital to living organisms
• Water


  • Makes up about 80% of a cell's contents
  • Is a reactant in important chemical reactions
  • Is a solvent for biological reactions
  • Transports substances
  • Helps with temperature control
  • Is a habitat for many organisms
• Water molecule


  One atom of oxygen joined to two atoms of hydrogen by shared electrons
• Water molecule


  • Has a partial negative charge on one side and a partial positive charge on the other, making it a polar molecule
  • The slightly negatively-charged oxygen atoms attract the slightly positively-charged hydrogen atoms of other water molecules, forming hydrogen bonds
• Hydrogen bonds between water molecules

  Give water a high specific heat capacity and high latent heat of evaporation
• Specific heat capacity


  The energy needed to raise the temperature of 1 gram of a substance by 1 °C
• Latent heat of evaporation

  The amount of energy used up when water evaporates
• Water's polarity


  • Makes it very cohesive, helping it to flow and be transported
  • Makes it a good solvent for ionic substances
• Water is less dense when it's solid (ice) than when it's liquid
• The less dense ice floating on top of water provides insulation, preventing the water below from freezing
• Carbohydrates are important biological molecules, the main energy supply in living organisms
• Polymer


  A molecule made up of many similar, smaller molecules (monomers) bonded together
• Monosaccharide


  The monomers that make up carbohydrates
• Monosaccharides


  • Glucose
  • Ribose
• Glucose


  • A hexose monosaccharide with two forms: alpha and beta
  • Its structure makes it soluble and a good energy source
• Ribose


  A pentose monosaccharide, the sugar component of RNA
• Monosaccharides joining to form larger molecules

  1. Condensation reaction to form disaccharides and polysaccharides

  2. Hydrolysis reaction to break apart glycosidic bonds
• Disaccharide


  Two monosaccharides joined together by a glycosidic bond
• Disaccharides


  • Maltose
  • Sucrose
  • Lactose
• Polysaccharide


  More than two monosaccharides joined together by glycosidic bonds
• Starch


  • The main energy storage material in plants, consisting of amylose and amylopectin
  • Amylose is a long, unbranched chain of alpha-glucose, good for compact storage
  • Amylopectin is a branched chain of alpha-glucose, allowing quick release of glucose
• Glycogen


  • The main energy storage material in animals, similar structure to amylopectin but with more branches for quick release of glucose
• Cellulose


  • The major component of plant cell walls, made of long, unbranched chains of beta-glucose linked by hydrogen bonds to form strong fibres
• Cellulose provides structural support for plant cells
• Cellulose


  Chains of cellulose linked together by hydrogen bonds to form strong fibres called microfibrils
• Function of cellulose


  Provides structural support for cells (e.g. in plant cell walls)
• Mannose is a hexose monosaccharide
• Triglycerides


  Macromolecules with one molecule of glycerol and three fatty acids attached
• Lipids


  Contain the chemical elements carbon, hydrogen and oxygen
• Fatty acid


  Molecules with long 'tails' made of hydrocarbons
• Hydrophobic


  Fatty acid tails repel water molecules
• Ester bond


  Formed between each fatty acid and the glycerol molecule in triglycerides
• Synthesis of triglycerides


  Esterification - condensation reaction where water molecule is released
• Breakdown of triglycerides


  Hydrolysis - water molecule is used up to break ester bonds
• Saturated fatty acid


  No double bonds between carbon atoms, 'saturated' with hydrogen
• Unsaturated fatty acid


  At least one double bond between carbon atoms, causing chain to kink
• Phospholipid


  Similar to triglycerides but one fatty acid replaced by a phosphate group
• Phospholipid bilayer


  Phospholipids form a double layer in cell membranes, with hydrophilic heads facing water and hydrophobic tails facing inwards
• Cholesterol


  Lipid with a hydrocarbon ring structure and a polar hydroxyl group, helps regulate fluidity of cell membranes
• Triglycerides are used for energy storage in animals and plants, and by some bacteria to store energy and carbon</b>