Biological molecules

• Water

  A very important molecule which is a major component of cells
• Water

  • It is a polar molecule due to uneven distribution of charge within the molecule
  • It is a metabolite in metabolic reactions such as condensation and hydrolysis which are used in forming and breaking of chemical bonds
  • It is a solvent in which many metabolic reactions occur
  • It has a high heat specific capacity meaning that a lot of energy is required to warm water up therefore minimising temperature fluctuations in living things therefore it acts as a buffer
  • It has a relatively large latent heat of vaporisation, meaning evaporation of water provides a cooling effect with little water loss
  • Strong cohesion between molecules enables effective transport of water in tube-like transport cells as the strong cohesion supports columns of water
  • Maximum density of water is at 4 degrees – this means that ice is less dense than water and floats on top of it creating an insulating layer, this increases the chance of survival of organisms in large bodies of water as it prevents them from freezing
  • Water is incompressible therefore it provides good support
• Monomers

  Small units which are the components of larger molecules
• Polymers

  Molecules made from monomers joined together
• Condensation reaction

  Joins monomers by chemical bonds and it involves the elimination of a water molecule
• Hydrolysis


  The opposite of condensation and it's when water is added to break a chemical bond between two molecules
• Carbohydrates


  Molecules which consist only of carbon, hydrogen and oxygen and they are long chains of sugar units called saccharides
• Types of saccharides


  • Monosaccharides
  • Disaccharides
  • Polysaccharides
• Glycosidic bonds


  Bonds formed in condensation reactions that join monosaccharides to form disaccharides and polysaccharides

  
• Glucose


  A monosaccharide containing six carbon atoms in each molecule, it is the main substrate for respiration therefore it is of great importance
• Glucose


  • It has two isomers – alpha and beta glucose
• Disaccharides


  • Maltose
  • Sucrose
  • Lactose
• Polysaccharides


  • Glycogen
  • Starch
  • Cellulose
• Glycogen


  • It is the main energy storage molecule in animals and it's formed from many molecules of alpha glucose joined together by 1, 4 and 1, 6 glycosidic bonds
  • It has a large number of side branches meaning that glucose & therefore energy, can be released quickly
  • It is a relatively large but compact molecule thus maximising the amount of energy it can store
• Starch


  • It stores energy in plants and it is a mixture of two polysaccharides called amylose and amylopectin
  • Amylose – an unbranched chain of glucose molecules joined by 1, 4 glycosidic bonds, as a result of that amylose is coiled and thus it is a very compact molecule meaning it can store a lot of energy
  • Amylopectin is branched and is made up of glucose molecules joined by 1, 4 and 1, 6 glycosidic bonds, due to the presence of many side branches it is rapidly digested by enzymes therefore energy is released quickly
• Cellulose


  • It is a component of cells wells in plants and it's composed of long, unbranched chains of beta glucose which are joined by glycosidic bonds
  • Microfibrils are strong threads which are made of long cellulose chains joined together by hydrogen bonds and they provide structural support in plants cells
• Lipids


  Biological molecules which are only soluble in organic solvents such as alcohols

  
• Types of lipids


  • Saturated lipids
  • Unsaturated lipids
• Saturated lipids


  • Don't contain any carbon-carbon double bonds

  
• Unsaturated lipids


  • Contain carbon-carbon double bonds and melt at lower temperatures than saturated fats
• Triglycerides


  Lipids made of one molecule of glycerol and three fatty acids joined by ester bonds formed in condensation reactions

  
• Phospholipids


  One of the fatty acids of a triglyceride is substituted by a phosphate-containing group, the phosphate heads are hydrophilic and the tails are hydrophobic and as a result phospholipids form micelles when they are in contact with water

  
• Essential inorganic ions


  • Hydrogen ions
  • Iron ions
  • Sodium ions
  • Phosphate ions
• Amino acids


  The monomers from which proteins are made, they contain an amino group – NH2, carboxylic acid group and a variable R group which is a carbon-containing chain

  
• Peptide bonds


  Bonds formed in condensation reactions that join amino acids
• Dipeptide


  Contains two amino acids
• Polypeptides


  Contain three or more amino acids
• Levels of protein structure

  • Primary structure
  • Secondary structure
  • Tertiary structure
• Primary structure


  • The order and number of amino acids in a protein
• Secondary structure


  • The shape that the chain of amino acids takes – either alpha helix or beta pleated sheet, determined by hydrogen bonding

  
• Tertiary structure


  • The 3D shape of the protein, can be globular or fibrous
• Collagen


  • A fibrous protein of great strength due to presence of both hydrogen and covalent bonds in the structure, collagen molecules wrap around each other and form fibrils which form strong collagen fibres, it forms the structure of bones, cartilage and connective tissue and is a main component of tendons which connect muscles to bones
• Haemoglobin


  • A water soluble globular protein which consists of two alpha and two beta polypeptide chains each containing a haem group, it carries oxygen in the blood as oxygen can bind to the haem (Fe2+) group and oxygen is then released when required