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  2. 2. Introduction <ul><li>Living systems are composed of a limited number of elements namely… </li></ul>CARBON, HYDROGEN, OXYGEN, NITROGEN, PHOSPHORUS & SULPHUR <ul><li>The carbon atom is of central biological importance as it can form 4 covalent bonds with other atoms </li></ul><ul><li>This allows a variety of complex molecules to be constructed </li></ul><ul><li>Many functional chemical groups are also associated with biological molecules as they are important in biological systems </li></ul>
  3. 3. Polymers <ul><li>Many biologically important molecules are polymers composed of monomers linked together </li></ul><ul><li>Two monomers are joined together by removing water molecules. This is called a CONDENSATION reaction or DEHYDRATION synthesis </li></ul><ul><li>This can be reversed by adding (back) water -> HYDROLYSIS </li></ul><ul><li>This is an important feature of cell metabolism </li></ul>Dehydration Hydrolysis
  4. 4. <ul><li>Making and breaking chemical bonds involves ENERGY </li></ul><ul><li>Synthesising more complex structures REQUIRES energy. These are called ANABOLIC or BIOSYNTHETIC reactions </li></ul><ul><li>If there is little overall change in energy, the reactions are reversible </li></ul><ul><li>Cell metabolism is tightly controlled to avoid energy chaos </li></ul>
  5. 5. Carbohydrates <ul><li>Composed of CARBON, HYDROGEN & OXYGEN </li></ul>MONOSACCHARIDES ‘Single Sugars’ e.g. glucose, fructose - General formula (CH 2 O)n - classified by number of carbons they have n = 3 TRIOSE n = 5 PENTOSE n = 6 HEXOSE - structure can vary greatly depending on the number of C atoms and the arrangement of H and O atoms
  6. 6. Glucose (C 6 H 12 O 6 ) <ul><li>Hexose sugar </li></ul><ul><li>Can exist in different forms depending on the position of the carbonyl group (C=O) on the terminal carbon </li></ul><ul><li>Variations of C 6 H 12 O 6 are called isomers </li></ul><ul><li>If OH group on C5 projects to the right = D Form (most common) </li></ul><ul><li>on left = L Form </li></ul>D-GLUCOSE = straight chain form of glucose (C 6 H 12 O 6 )
  7. 7. <ul><li>In solution, glucose adopts a cyclic form where C 1 and C 5 are linked by an oxygen atom giving a ring structure ( see diagram ) </li></ul><ul><li>Depending on the position of the -OH group on C 1 whether: </li></ul><ul><ul><li>(  ) alpha - below C 1 </li></ul></ul><ul><ul><li>(  ) beta - above C 1 </li></ul></ul><ul><li>In solution the equilibrium proportions of the three forms are approximately 38%  to 62%  to 0.02% straight chain glucose at any given time </li></ul>
  8. 8. The Glycosidic Bond <ul><li>2 monomers (monosaccharides) can be linked by DEHYDRATION SYNTHESIS or the CONDENSATION REACTION , to give a disaccharide </li></ul><ul><li>The carbohydrate’s name is defined by the component monomers and the way the bond is arranged </li></ul><ul><li>Common disaccharides are : </li></ul><ul><ul><li>SUCROSE = Glucose + Fructose </li></ul></ul><ul><ul><li>LACTOSE = Glucose + Galactose </li></ul></ul>ANIMATION
  9. 9. Polysaccharides <ul><li>Long chains of simple sugars e.g. starch , glycogen and cellulose </li></ul><ul><li>If the repeating monomers are the same , they form a homopolymer . If they are different they form a heteropolymer </li></ul><ul><li>Polysaccharides are insoluble in water and so make ideal storage compounds </li></ul><ul><li>The following three polysaccharides are all homopolymers of glucose but they have different functions and properties depending on their structure </li></ul>
  10. 10. 1. Starch <ul><li>Found in plants </li></ul><ul><li>Helical arrangement of glucose </li></ul><ul><li>Storage polysaccharide of energy </li></ul><ul><li>Can be easily hydrolysed to release monomers of glucose for energy </li></ul><ul><li>Starch test : turns iodine from dark brown to blue/black </li></ul>
  11. 11. 2. Glycogen <ul><li>Storage compound in animals, generally found in the liver </li></ul><ul><li>Polymer of glucose linked by  1-6 bonds and  1-4 bonds </li></ul><ul><li>Short term energy store </li></ul><ul><li>Plays a role in homeostatic control of blood sugar level </li></ul><ul><li>Remains dark brown with iodine </li></ul>
  12. 12. 3. Cellulose <ul><li>Storage compound in plants </li></ul><ul><li>Parallel chain arrangement linked by  1-4 glycosidic bonds and hydrogen bonding between parallel chains </li></ul><ul><li>Doesn’t stain with iodine </li></ul><ul><li>Very tough arrangement of fibres due to structural arrangement </li></ul><ul><li>most abundant organic material on Earth </li></ul><ul><li>Most animals lack cellulase, the enzyme needed to breakdown the component monomers </li></ul>
  13. 13. 4. Chitin <ul><ul><li>A homopolysaccharide similar to cellulose in structure. Component of many insect exoskeletons - very strong and rigid; also resistant to chemicals. </li></ul></ul>5. Glycosaminoglycans <ul><ul><li>A heteropolymer found in skin and connective tissue of vertebrates </li></ul></ul>
  14. 14. Summary of Carbohydrate Functions <ul><li>Immediate respiratory substrate e.g. glucose </li></ul><ul><li>Energy stores e.g. glycogen in mammals, starch in plants </li></ul><ul><li>Structural components e.g. cellulose in plant cell walls, chitin in insect exoskeleton, pentose sugars (ribose & deoxyribose in RNA & DNA) </li></ul><ul><li>Metabolites i.e. intermediates in biochemical pathways </li></ul><ul><li>Cell to cell attachment molecules e.g. glycoproteins or glycolipids on the plasma membrane </li></ul><ul><li>Transport e.g. sucrose in plant phloem tissue </li></ul>