Biological molecules

• Carbohydrates


  Consist of elements Carbon, Hydrogen and Oxygen
• Monosaccharides


  • Soluble in water
  • Sweet tasting
  • Form crystals
• Monosaccharides


  • Alpha glucose (a glucose)
  • Beta glucose (§ glucose)
• Alpha glucose


  Easily transported (water soluble) and readily used in respiration OH group on C1 is above C4
• Beta glucose


  Found in cellulose, same molecular formula as alpha glucose but OH group on C1 is above the Carbon and below on C4
• Disaccharides


  Two monosaccharide sugars joined together by a condensation reaction, removing a water molecule and forming a glycosidic bond
• Disaccharides


  • Maltose
  • Sucrose
  • Lactose
• Maltose


  Disaccharide formed by condensation of two glucose molecules
• Sucrose


  Disaccharide formed by condensation of glucose and fructose
• Lactose


  Disaccharide formed by condensation of glucose and galactose
• Polysaccharides

  Polymers formed by combining many monosaccharide molecules by glycosidic bonds formed during condensation reactions
• Starch


  • Coiled, compact (can be stored in a small space)polysaccharide made from two polymers amylose and amylopectin
  • Insoluble, does not affect water potential
  • Glycosidic bonds can be hydrolysed to form glucose monomers
• Amylose


  Glucose monomers joined by 1,4 glycosidic bonds
• Amylopectin


  Glucose monomers joined by 1,4 and 1,6 glycosidic bonds, forming branches
• Glycogen


  • Large, insoluble polysaccharide with more branches and shorter chains than starch
  • Insoluble, does not affect water potential
  • Highly branched so many ends, glycosidic bonds can be rapidly hydrolysed by enzymes
• Cellulose


  • Straight, unbranched, structural polysaccharide forming plant cell walls
  • Made of β glucose monomers held together by 1,4 glycosidic bonds
  • Parallel chains held together by hydrogen bonds, forming microfibrils that support the cell wall
• Formation of triglyceride


  1. One Glycerol

  2. Three fatty acids

  3. Three covalent ester bonds formed in condensation reactions

  4. Three molecules of water released
• Functions of triglycerides


  • Source of energy - lipids have a higher proportion of hydrogen to oxygen atoms and when oxidised release twice the energy as the same mass as carbohydrates and proteins
  • Act as insulators - fat is a slow conductor of heat and helps retain body heat (thermal insulator), also acts as an electrical insulator as the myelin sheath in nerve cells
  • Waterproofing - Are large non-polar molecules which are insoluble in water, therefore useful for waterproofing eg waxy cuticle in plants
  • Protection - fat is stored around delicate organs and acts as a shock absorber
• Saturated triglycerides - Fatty acid has no C=C bonds, all the carbon atoms are linked to the maximum number of hydrogen atoms.
• Phospholipids

  • 2 fatty acid tails
  • 1 glycerol
  • 1 phosphate group/head
• Phospholipid bilayer

  In water phospholipids form a bilayer - the hydrophobic tails point towards the centre of the bilayer, the hydrophilic heads point outwards
• Formation of Dipeptides and Polypeptides


  1. Amino acids join together

  2. Condensation reaction occurs between carboxyll group of one amino acid and amine group of another

  3. Forms a strong covalent bond called a peptide bond

  4. Molecules formed are dipeptide and a water molecule
• Primary Structure

  The sequence of amino acids held together by peptide bonds. The primary structure determines the secondary and tertiary structure and thus the final 3D shape of the protein.
• Secondary Structure

  Folding of the primary structure - the polypeptide chain coils to form an alpha helix or folds to form a beta pleated sheet. Both these secondary structures are held together by many weak hydrogen bonds which overall make the structure
• Tertiary Structure


  This is the further folding of the polypeptide chain to give a more complex 3D shape and is closely related to the function of a particular protein. The tertiary structure is stabilised by: Hydrogen bonds, Ionic Bonds, Disulphide bonds, Hydrophobic interactions
• Quaternary Structure


  These are proteins which are made up of more than one polypeptide chain e.g. haemoglobin. Haemoglobin consists of 4 polypeptide chains. There are 2 a chains and 2 B chains. Each chain has a haem group which contains a Fe?+ ion. This haem group gives blood its colour. Haemoglobins function is to carry oxygen from the lungs to the respiring tissues.
• Fibrous Proteins


  • Form long fibres, have regular, repetitive sequences of amino acids and are usually insoluble in water. They tend to have structural roles in living organisms: e.g. myosin in muscles, keratin in hair, collagen in skin.
• Collagen


  Found in skin, bones and ligaments. It is made from three identical left handed helix polypeptide chains wound around each other to form a triple helix (quaternary structure). In each polypeptide chain every third amino acid is glycine. Glycine is small so it allows 3 polypeptides to pack closely together. 3 chains held together by hydrogen-bonds. Collagen molecules cross-link through covalent bonds to form fibres which give collagen its great strength.
• Globular Proteins

  • These fold up into a compact ball like shape. Hydrophobic R- groups on amino acids tend to be turn inwards towards the centre of the protein and hydrophilic R -groups tend to be on the outside. This means that they tend to be more water soluble than fibrous proteins. Globular proteins tend to have a metabolic role in living organisms e.g. all enzymes, plasma proteins and antibodies have globular structure. Globular proteins have a wide range of amino acid sequence in their structure.